[perl5.git] / perlio.c

/*
 * perlio.c
 * Copyright (c) 1996-2006, Nick Ing-Simmons
 * Copyright (c) 2006, 2007, Larry Wall and others
 *
 * You may distribute under the terms of either the GNU General Public License
 * or the Artistic License, as specified in the README file.
 */

/*
 * Hour after hour for nearly three weary days he had jogged up and down,
 * over passes, and through long dales, and across many streams.
 */

/* This file contains the functions needed to implement PerlIO, which
 * is Perl's private replacement for the C stdio library. This is used
 * by default unless you compile with -Uuseperlio or run with
 * PERLIO=:stdio (but don't do this unless you know what you're doing)
 */

/*
 * If we have ActivePerl-like PERL_IMPLICIT_SYS then we need a dTHX to get
 * at the dispatch tables, even when we do not need it for other reasons.
 * Invent a dSYS macro to abstract this out
 */
#ifdef PERL_IMPLICIT_SYS
#define dSYS dTHX
#else
#define dSYS dNOOP
#endif

#define VOIDUSED 1
#ifdef PERL_MICRO
#   include "uconfig.h"
#else
#   ifndef USE_CROSS_COMPILE
#       include "config.h"
#   else
#       include "xconfig.h"
#   endif
#endif

#define PERLIO_NOT_STDIO 0
#if !defined(PERLIO_IS_STDIO) && !defined(USE_SFIO)
/*
 * #define PerlIO FILE
 */
#endif
/*
 * This file provides those parts of PerlIO abstraction
 * which are not #defined in perlio.h.
 * Which these are depends on various Configure #ifdef's
 */

#include "EXTERN.h"
#define PERL_IN_PERLIO_C
#include "perl.h"

#ifdef PERL_IMPLICIT_CONTEXT
#undef dSYS
#define dSYS dTHX
#endif

#include "XSUB.h"

#ifdef __Lynx__
/* Missing proto on LynxOS */
int mkstemp(char*);
#endif

/* Call the callback or PerlIOBase, and return failure. */
#define Perl_PerlIO_or_Base(f, callback, base, failure, args) 	\
	if (PerlIOValid(f)) {					\
		const PerlIO_funcs * const tab = PerlIOBase(f)->tab;\
		if (tab && tab->callback)			\
			return (*tab->callback) args;		\
		else						\
			return PerlIOBase_ ## base args;	\
	}							\
	else							\
		SETERRNO(EBADF, SS_IVCHAN);			\
	return failure

/* Call the callback or fail, and return failure. */
#define Perl_PerlIO_or_fail(f, callback, failure, args) 	\
	if (PerlIOValid(f)) {					\
		const PerlIO_funcs * const tab = PerlIOBase(f)->tab;\
		if (tab && tab->callback)			\
			return (*tab->callback) args;		\
		SETERRNO(EINVAL, LIB_INVARG);			\
	}							\
	else							\
		SETERRNO(EBADF, SS_IVCHAN);			\
	return failure

/* Call the callback or PerlIOBase, and be void. */
#define Perl_PerlIO_or_Base_void(f, callback, base, args) 	\
	if (PerlIOValid(f)) {					\
		const PerlIO_funcs * const tab = PerlIOBase(f)->tab;\
		if (tab && tab->callback)			\
			(*tab->callback) args;			\
		else						\
			PerlIOBase_ ## base args;		\
	}							\
	else							\
		SETERRNO(EBADF, SS_IVCHAN)

/* Call the callback or fail, and be void. */
#define Perl_PerlIO_or_fail_void(f, callback, args) 		\
	if (PerlIOValid(f)) {					\
		const PerlIO_funcs * const tab = PerlIOBase(f)->tab;\
		if (tab && tab->callback)			\
			(*tab->callback) args;			\
		else						\
			SETERRNO(EINVAL, LIB_INVARG);		\
	}							\
	else							\
		SETERRNO(EBADF, SS_IVCHAN)

#if defined(__osf__) && _XOPEN_SOURCE < 500
extern int   fseeko(FILE *, off_t, int);
extern off_t ftello(FILE *);
#endif

#ifndef USE_SFIO

EXTERN_C int perlsio_binmode(FILE *fp, int iotype, int mode);

int
perlsio_binmode(FILE *fp, int iotype, int mode)
{
    /*
     * This used to be contents of do_binmode in doio.c
     */
#ifdef DOSISH
#  if defined(atarist) || defined(__MINT__)
    PERL_UNUSED_ARG(iotype);
    if (!fflush(fp)) {
        if (mode & O_BINARY)
            ((FILE *) fp)->_flag |= _IOBIN;
        else
            ((FILE *) fp)->_flag &= ~_IOBIN;
        return 1;
    }
    return 0;
#  else
    dTHX;
    PERL_UNUSED_ARG(iotype);
#ifdef NETWARE
    if (PerlLIO_setmode(fp, mode) != -1) {
#else
    if (PerlLIO_setmode(fileno(fp), mode) != -1) {
#endif
#    if defined(WIN32) && defined(__BORLANDC__)
        /*
         * The translation mode of the stream is maintained independent 
of
         * the translation mode of the fd in the Borland RTL (heavy
         * digging through their runtime sources reveal).  User has to 
set
         * the mode explicitly for the stream (though they don't 
document
         * this anywhere). GSAR 97-5-24
         */
        fseek(fp, 0L, 0);
        if (mode & O_BINARY)
            fp->flags |= _F_BIN;
        else
            fp->flags &= ~_F_BIN;
#    endif
        return 1;
    }
    else
        return 0;
#  endif
#else
#  if defined(USEMYBINMODE)
    dTHX;
#    if defined(__CYGWIN__)
    PERL_UNUSED_ARG(iotype);
#    endif
    if (my_binmode(fp, iotype, mode) != FALSE)
        return 1;
    else
        return 0;
#  else
    PERL_UNUSED_ARG(fp);
    PERL_UNUSED_ARG(iotype);
    PERL_UNUSED_ARG(mode);
    return 1;
#  endif
#endif
}
#endif /* sfio */

#ifndef O_ACCMODE
#define O_ACCMODE 3             /* Assume traditional implementation */
#endif

int
PerlIO_intmode2str(int rawmode, char *mode, int *writing)
{
    const int result = rawmode & O_ACCMODE;
    int ix = 0;
    int ptype;
    switch (result) {
    case O_RDONLY:
	ptype = IoTYPE_RDONLY;
	break;
    case O_WRONLY:
	ptype = IoTYPE_WRONLY;
	break;
    case O_RDWR:
    default:
	ptype = IoTYPE_RDWR;
	break;
    }
    if (writing)
	*writing = (result != O_RDONLY);

    if (result == O_RDONLY) {
	mode[ix++] = 'r';
    }
#ifdef O_APPEND
    else if (rawmode & O_APPEND) {
	mode[ix++] = 'a';
	if (result != O_WRONLY)
	    mode[ix++] = '+';
    }
#endif
    else {
	if (result == O_WRONLY)
	    mode[ix++] = 'w';
	else {
	    mode[ix++] = 'r';
	    mode[ix++] = '+';
	}
    }
    if (rawmode & O_BINARY)
	mode[ix++] = 'b';
    mode[ix] = '\0';
    return ptype;
}

#ifndef PERLIO_LAYERS
int
PerlIO_apply_layers(pTHX_ PerlIO *f, const char *mode, const char *names)
{
    if (!names || !*names
        || strEQ(names, ":crlf")
        || strEQ(names, ":raw")
        || strEQ(names, ":bytes")
       ) {
	return 0;
    }
    Perl_croak(aTHX_ "Cannot apply \"%s\" in non-PerlIO perl", names);
    /*
     * NOTREACHED
     */
    return -1;
}

void
PerlIO_destruct(pTHX)
{
}

int
PerlIO_binmode(pTHX_ PerlIO *fp, int iotype, int mode, const char *names)
{
#ifdef USE_SFIO
    PERL_UNUSED_ARG(iotype);
    PERL_UNUSED_ARG(mode);
    PERL_UNUSED_ARG(names);
    return 1;
#else
    return perlsio_binmode(fp, iotype, mode);
#endif
}

PerlIO *
PerlIO_fdupopen(pTHX_ PerlIO *f, CLONE_PARAMS *param, int flags)
{
#if defined(PERL_MICRO) || defined(__SYMBIAN32__)
    return NULL;
#else
#ifdef PERL_IMPLICIT_SYS
    return PerlSIO_fdupopen(f);
#else
#ifdef WIN32
    return win32_fdupopen(f);
#else
    if (f) {
	const int fd = PerlLIO_dup(PerlIO_fileno(f));
	if (fd >= 0) {
	    char mode[8];
#ifdef DJGPP
	    const int omode = djgpp_get_stream_mode(f);
#else
	    const int omode = fcntl(fd, F_GETFL);
#endif
	    PerlIO_intmode2str(omode,mode,NULL);
	    /* the r+ is a hack */
	    return PerlIO_fdopen(fd, mode);
	}
	return NULL;
    }
    else {
	SETERRNO(EBADF, SS_IVCHAN);
    }
#endif
    return NULL;
#endif
#endif
}


/*
 * De-mux PerlIO_openn() into fdopen, freopen and fopen type entries
 */

PerlIO *
PerlIO_openn(pTHX_ const char *layers, const char *mode, int fd,
	     int imode, int perm, PerlIO *old, int narg, SV **args)
{
    if (narg) {
	if (narg > 1) {
	    Perl_croak(aTHX_ "More than one argument to open");
	}
	if (*args == &PL_sv_undef)
	    return PerlIO_tmpfile();
	else {
	    const char *name = SvPV_nolen_const(*args);
	    if (*mode == IoTYPE_NUMERIC) {
		fd = PerlLIO_open3(name, imode, perm);
		if (fd >= 0)
		    return PerlIO_fdopen(fd, mode + 1);
	    }
	    else if (old) {
		return PerlIO_reopen(name, mode, old);
	    }
	    else {
		return PerlIO_open(name, mode);
	    }
	}
    }
    else {
	return PerlIO_fdopen(fd, (char *) mode);
    }
    return NULL;
}

XS(XS_PerlIO__Layer__find)
{
    dXSARGS;
    if (items < 2)
	Perl_croak(aTHX_ "Usage class->find(name[,load])");
    else {
	const char * const name = SvPV_nolen_const(ST(1));
	ST(0) = (strEQ(name, "crlf")
		 || strEQ(name, "raw")) ? &PL_sv_yes : &PL_sv_undef;
	XSRETURN(1);
    }
}


void
Perl_boot_core_PerlIO(pTHX)
{
    newXS("PerlIO::Layer::find", XS_PerlIO__Layer__find, __FILE__);
}

#endif


#ifdef PERLIO_IS_STDIO

void
PerlIO_init(pTHX)
{
    PERL_UNUSED_CONTEXT;
    /*
     * Does nothing (yet) except force this file to be included in perl
     * binary. That allows this file to force inclusion of other functions
     * that may be required by loadable extensions e.g. for
     * FileHandle::tmpfile
     */
}

#undef PerlIO_tmpfile
PerlIO *
PerlIO_tmpfile(void)
{
    return tmpfile();
}

#else                           /* PERLIO_IS_STDIO */

#ifdef USE_SFIO

#undef HAS_FSETPOS
#undef HAS_FGETPOS

/*
 * This section is just to make sure these functions get pulled in from
 * libsfio.a
 */

#undef PerlIO_tmpfile
PerlIO *
PerlIO_tmpfile(void)
{
    return sftmp(0);
}

void
PerlIO_init(pTHX)
{
    PERL_UNUSED_CONTEXT;
    /*
     * Force this file to be included in perl binary. Which allows this
     * file to force inclusion of other functions that may be required by
     * loadable extensions e.g. for FileHandle::tmpfile
     */

    /*
     * Hack sfio does its own 'autoflush' on stdout in common cases. Flush
     * results in a lot of lseek()s to regular files and lot of small
     * writes to pipes.
     */
    sfset(sfstdout, SF_SHARE, 0);
}

/* This is not the reverse of PerlIO_exportFILE(), PerlIO_releaseFILE() is. */
PerlIO *
PerlIO_importFILE(FILE *stdio, const char *mode)
{
    const int fd = fileno(stdio);
    if (!mode || !*mode) {
	mode = "r+";
    }
    return PerlIO_fdopen(fd, mode);
}

FILE *
PerlIO_findFILE(PerlIO *pio)
{
    const int fd = PerlIO_fileno(pio);
    FILE * const f = fdopen(fd, "r+");
    PerlIO_flush(pio);
    if (!f && errno == EINVAL)
	f = fdopen(fd, "w");
    if (!f && errno == EINVAL)
	f = fdopen(fd, "r");
    return f;
}


#else                           /* USE_SFIO */
/*======================================================================================*/
/*
 * Implement all the PerlIO interface ourselves.
 */

#include "perliol.h"

/*
 * We _MUST_ have <unistd.h> if we are using lseek() and may have large
 * files
 */
#ifdef I_UNISTD
#include <unistd.h>
#endif
#ifdef HAS_MMAP
#include <sys/mman.h>
#endif

void
PerlIO_debug(const char *fmt, ...)
{
    va_list ap;
    dSYS;
    va_start(ap, fmt);
    if (!PL_perlio_debug_fd) {
	if (!PL_tainting && PL_uid == PL_euid && PL_gid == PL_egid) {
	    const char * const s = PerlEnv_getenv("PERLIO_DEBUG");
	    if (s && *s)
		PL_perlio_debug_fd
		    = PerlLIO_open3(s, O_WRONLY | O_CREAT | O_APPEND, 0666);
	    else
		PL_perlio_debug_fd = -1;
	} else {
	    /* tainting or set*id, so ignore the environment, and ensure we
	       skip these tests next time through.  */
	    PL_perlio_debug_fd = -1;
	}
    }
    if (PL_perlio_debug_fd > 0) {
	dTHX;
#ifdef USE_ITHREADS
	const char * const s = CopFILE(PL_curcop);
	/* Use fixed buffer as sv_catpvf etc. needs SVs */
	char buffer[1024];
	const STRLEN len1 = my_snprintf(buffer, sizeof(buffer), "%.40s:%" IVdf " ", s ? s : "(none)", (IV) CopLINE(PL_curcop));
	const STRLEN len2 = my_vsnprintf(buffer + len1, sizeof(buffer) - len1, fmt, ap);
	PerlLIO_write(PL_perlio_debug_fd, buffer, len1 + len2);
#else
	const char *s = CopFILE(PL_curcop);
	STRLEN len;
	SV * const sv = Perl_newSVpvf(aTHX_ "%s:%" IVdf " ", s ? s : "(none)",
				      (IV) CopLINE(PL_curcop));
	Perl_sv_vcatpvf(aTHX_ sv, fmt, &ap);

	s = SvPV_const(sv, len);
	PerlLIO_write(PL_perlio_debug_fd, s, len);
	SvREFCNT_dec(sv);
#endif
    }
    va_end(ap);
}

/*--------------------------------------------------------------------------------------*/

/*
 * Inner level routines
 */

/*
 * Table of pointers to the PerlIO structs (malloc'ed)
 */
#define PERLIO_TABLE_SIZE 64

PerlIO *
PerlIO_allocate(pTHX)
{
    dVAR;
    /*
     * Find a free slot in the table, allocating new table as necessary
     */
    PerlIO **last;
    PerlIO *f;
    last = &PL_perlio;
    while ((f = *last)) {
	int i;
	last = (PerlIO **) (f);
	for (i = 1; i < PERLIO_TABLE_SIZE; i++) {
	    if (!*++f) {
		return f;
	    }
	}
    }
    Newxz(f,PERLIO_TABLE_SIZE,PerlIO);
    if (!f) {
	return NULL;
    }
    *last = f;
    return f + 1;
}

#undef PerlIO_fdupopen
PerlIO *
PerlIO_fdupopen(pTHX_ PerlIO *f, CLONE_PARAMS *param, int flags)
{
    if (PerlIOValid(f)) {
	const PerlIO_funcs * const tab = PerlIOBase(f)->tab;
	PerlIO_debug("fdupopen f=%p param=%p\n",(void*)f,(void*)param);
	if (tab && tab->Dup)
	     return (*tab->Dup)(aTHX_ PerlIO_allocate(aTHX), f, param, flags);
	else {
	     return PerlIOBase_dup(aTHX_ PerlIO_allocate(aTHX), f, param, flags);
	}
    }
    else
	 SETERRNO(EBADF, SS_IVCHAN);

    return NULL;
}

void
PerlIO_cleantable(pTHX_ PerlIO **tablep)
{
    PerlIO * const table = *tablep;
    if (table) {
	int i;
	PerlIO_cleantable(aTHX_(PerlIO **) & (table[0]));
	for (i = PERLIO_TABLE_SIZE - 1; i > 0; i--) {
	    PerlIO * const f = table + i;
	    if (*f) {
		PerlIO_close(f);
	    }
	}
	Safefree(table);
	*tablep = NULL;
    }
}


PerlIO_list_t *
PerlIO_list_alloc(pTHX)
{
    PerlIO_list_t *list;
    PERL_UNUSED_CONTEXT;
    Newxz(list, 1, PerlIO_list_t);
    list->refcnt = 1;
    return list;
}

void
PerlIO_list_free(pTHX_ PerlIO_list_t *list)
{
    if (list) {
	if (--list->refcnt == 0) {
	    if (list->array) {
		IV i;
		for (i = 0; i < list->cur; i++) {
		    if (list->array[i].arg)
			SvREFCNT_dec(list->array[i].arg);
		}
		Safefree(list->array);
	    }
	    Safefree(list);
	}
    }
}

void
PerlIO_list_push(pTHX_ PerlIO_list_t *list, PerlIO_funcs *funcs, SV *arg)
{
    dVAR;
    PerlIO_pair_t *p;
    PERL_UNUSED_CONTEXT;

    if (list->cur >= list->len) {
	list->len += 8;
	if (list->array)
	    Renew(list->array, list->len, PerlIO_pair_t);
	else
	    Newx(list->array, list->len, PerlIO_pair_t);
    }
    p = &(list->array[list->cur++]);
    p->funcs = funcs;
    if ((p->arg = arg)) {
	SvREFCNT_inc_simple_void_NN(arg);
    }
}

PerlIO_list_t *
PerlIO_clone_list(pTHX_ PerlIO_list_t *proto, CLONE_PARAMS *param)
{
    PerlIO_list_t *list = NULL;
    if (proto) {
	int i;
	list = PerlIO_list_alloc(aTHX);
	for (i=0; i < proto->cur; i++) {
	    SV *arg = proto->array[i].arg;
#ifdef sv_dup
	    if (arg && param)
		arg = sv_dup(arg, param);
#else
	    PERL_UNUSED_ARG(param);
#endif
	    PerlIO_list_push(aTHX_ list, proto->array[i].funcs, arg);
	}
    }
    return list;
}

void
PerlIO_clone(pTHX_ PerlInterpreter *proto, CLONE_PARAMS *param)
{
#ifdef USE_ITHREADS
    PerlIO **table = &proto->Iperlio;
    PerlIO *f;
    PL_perlio = NULL;
    PL_known_layers = PerlIO_clone_list(aTHX_ proto->Iknown_layers, param);
    PL_def_layerlist = PerlIO_clone_list(aTHX_ proto->Idef_layerlist, param);
    PerlIO_allocate(aTHX); /* root slot is never used */
    PerlIO_debug("Clone %p from %p\n",(void*)aTHX,(void*)proto);
    while ((f = *table)) {
	    int i;
	    table = (PerlIO **) (f++);
	    for (i = 1; i < PERLIO_TABLE_SIZE; i++) {
		if (*f) {
		    (void) fp_dup(f, 0, param);
		}
		f++;
	    }
	}
#else
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(proto);
    PERL_UNUSED_ARG(param);
#endif
}

void
PerlIO_destruct(pTHX)
{
    dVAR;
    PerlIO **table = &PL_perlio;
    PerlIO *f;
#ifdef USE_ITHREADS
    PerlIO_debug("Destruct %p\n",(void*)aTHX);
#endif
    while ((f = *table)) {
	int i;
	table = (PerlIO **) (f++);
	for (i = 1; i < PERLIO_TABLE_SIZE; i++) {
	    PerlIO *x = f;
	    const PerlIOl *l;
	    while ((l = *x)) {
		if (l->tab->kind & PERLIO_K_DESTRUCT) {
		    PerlIO_debug("Destruct popping %s\n", l->tab->name);
		    PerlIO_flush(x);
		    PerlIO_pop(aTHX_ x);
		}
		else {
		    x = PerlIONext(x);
		}
	    }
	    f++;
	}
    }
}

void
PerlIO_pop(pTHX_ PerlIO *f)
{
    const PerlIOl *l = *f;
    if (l) {
	PerlIO_debug("PerlIO_pop f=%p %s\n", (void*)f, l->tab->name);
	if (l->tab->Popped) {
	    /*
	     * If popped returns non-zero do not free its layer structure
	     * it has either done so itself, or it is shared and still in
	     * use
	     */
	    if ((*l->tab->Popped) (aTHX_ f) != 0)
		return;
	}
	*f = l->next;
	Safefree(l);
    }
}

/* Return as an array the stack of layers on a filehandle.  Note that
 * the stack is returned top-first in the array, and there are three
 * times as many array elements as there are layers in the stack: the
 * first element of a layer triplet is the name, the second one is the
 * arguments, and the third one is the flags. */

AV *
PerlIO_get_layers(pTHX_ PerlIO *f)
{
    dVAR;
    AV * const av = newAV();

    if (PerlIOValid(f)) {
	PerlIOl *l = PerlIOBase(f);

	while (l) {
	    /* There is some collusion in the implementation of
	       XS_PerlIO_get_layers - it knows that name and flags are
	       generated as fresh SVs here, and takes advantage of that to
	       "copy" them by taking a reference. If it changes here, it needs
	       to change there too.  */
	    SV * const name = l->tab && l->tab->name ?
	    newSVpv(l->tab->name, 0) : &PL_sv_undef;
	    SV * const arg = l->tab && l->tab->Getarg ?
	    (*l->tab->Getarg)(aTHX_ &l, 0, 0) : &PL_sv_undef;
	    av_push(av, name);
	    av_push(av, arg);
	    av_push(av, newSViv((IV)l->flags));
	    l = l->next;
	}
    }

    return av;
}

/*--------------------------------------------------------------------------------------*/
/*
 * XS Interface for perl code
 */

PerlIO_funcs *
PerlIO_find_layer(pTHX_ const char *name, STRLEN len, int load)
{
    dVAR;
    IV i;
    if ((SSize_t) len <= 0)
	len = strlen(name);
    for (i = 0; i < PL_known_layers->cur; i++) {
	PerlIO_funcs * const f = PL_known_layers->array[i].funcs;
	if (memEQ(f->name, name, len) && f->name[len] == 0) {
	    PerlIO_debug("%.*s => %p\n", (int) len, name, (void*)f);
	    return f;
	}
    }
    if (load && PL_subname && PL_def_layerlist
	&& PL_def_layerlist->cur >= 2) {
	if (PL_in_load_module) {
	    Perl_croak(aTHX_ "Recursive call to Perl_load_module in PerlIO_find_layer");
	    return NULL;
	} else {
	    SV * const pkgsv = newSVpvs("PerlIO");
	    SV * const layer = newSVpvn(name, len);
	    CV * const cv    = Perl_get_cvn_flags(aTHX_ STR_WITH_LEN("PerlIO::Layer::NoWarnings"), 0);
	    ENTER;
	    SAVEINT(PL_in_load_module);
	    if (cv) {
		SAVEGENERICSV(PL_warnhook);
		PL_warnhook = (SV *) (SvREFCNT_inc_simple_NN(cv));
	    }
	    PL_in_load_module++;
	    /*
	     * The two SVs are magically freed by load_module
	     */
	    Perl_load_module(aTHX_ 0, pkgsv, NULL, layer, NULL);
	    PL_in_load_module--;
	    LEAVE;
	    return PerlIO_find_layer(aTHX_ name, len, 0);
	}
    }
    PerlIO_debug("Cannot find %.*s\n", (int) len, name);
    return NULL;
}

#ifdef USE_ATTRIBUTES_FOR_PERLIO

static int
perlio_mg_set(pTHX_ SV *sv, MAGIC *mg)
{
    if (SvROK(sv)) {
	IO * const io = GvIOn((GV *) SvRV(sv));
	PerlIO * const ifp = IoIFP(io);
	PerlIO * const ofp = IoOFP(io);
	Perl_warn(aTHX_ "set %" SVf " %p %p %p",
		  SVfARG(sv), (void*)io, (void*)ifp, (void*)ofp);
    }
    return 0;
}

static int
perlio_mg_get(pTHX_ SV *sv, MAGIC *mg)
{
    if (SvROK(sv)) {
	IO * const io = GvIOn((GV *) SvRV(sv));
	PerlIO * const ifp = IoIFP(io);
	PerlIO * const ofp = IoOFP(io);
	Perl_warn(aTHX_ "get %" SVf " %p %p %p",
		  SVfARG(sv), (void*)io, (void*)ifp, (void*)ofp);
    }
    return 0;
}

static int
perlio_mg_clear(pTHX_ SV *sv, MAGIC *mg)
{
    Perl_warn(aTHX_ "clear %" SVf, SVfARG(sv));
    return 0;
}

static int
perlio_mg_free(pTHX_ SV *sv, MAGIC *mg)
{
    Perl_warn(aTHX_ "free %" SVf, SVfARG(sv));
    return 0;
}

MGVTBL perlio_vtab = {
    perlio_mg_get,
    perlio_mg_set,
    NULL,                       /* len */
    perlio_mg_clear,
    perlio_mg_free
};

XS(XS_io_MODIFY_SCALAR_ATTRIBUTES)
{
    dXSARGS;
    SV * const sv = SvRV(ST(1));
    AV * const av = newAV();
    MAGIC *mg;
    int count = 0;
    int i;
    sv_magic(sv, (SV *) av, PERL_MAGIC_ext, NULL, 0);
    SvRMAGICAL_off(sv);
    mg = mg_find(sv, PERL_MAGIC_ext);
    mg->mg_virtual = &perlio_vtab;
    mg_magical(sv);
    Perl_warn(aTHX_ "attrib %" SVf, SVfARG(sv));
    for (i = 2; i < items; i++) {
	STRLEN len;
	const char * const name = SvPV_const(ST(i), len);
	SV * const layer = PerlIO_find_layer(aTHX_ name, len, 1);
	if (layer) {
	    av_push(av, SvREFCNT_inc_simple_NN(layer));
	}
	else {
	    ST(count) = ST(i);
	    count++;
	}
    }
    SvREFCNT_dec(av);
    XSRETURN(count);
}

#endif                          /* USE_ATTIBUTES_FOR_PERLIO */

SV *
PerlIO_tab_sv(pTHX_ PerlIO_funcs *tab)
{
    HV * const stash = gv_stashpvs("PerlIO::Layer", GV_ADD);
    SV * const sv = sv_bless(newRV_noinc(newSViv(PTR2IV(tab))), stash);
    return sv;
}

XS(XS_PerlIO__Layer__NoWarnings)
{
    /* This is used as a %SIG{__WARN__} handler to supress warnings
       during loading of layers.
     */
    dVAR;
    dXSARGS;
    PERL_UNUSED_ARG(cv);
    if (items)
    	PerlIO_debug("warning:%s\n",SvPV_nolen_const(ST(0)));
    XSRETURN(0);
}

XS(XS_PerlIO__Layer__find)
{
    dVAR;
    dXSARGS;
    PERL_UNUSED_ARG(cv);
    if (items < 2)
	Perl_croak(aTHX_ "Usage class->find(name[,load])");
    else {
	STRLEN len;
	const char * const name = SvPV_const(ST(1), len);
	const bool load = (items > 2) ? SvTRUE(ST(2)) : 0;
	PerlIO_funcs * const layer = PerlIO_find_layer(aTHX_ name, len, load);
	ST(0) =
	    (layer) ? sv_2mortal(PerlIO_tab_sv(aTHX_ layer)) :
	    &PL_sv_undef;
	XSRETURN(1);
    }
}

void
PerlIO_define_layer(pTHX_ PerlIO_funcs *tab)
{
    dVAR;
    if (!PL_known_layers)
	PL_known_layers = PerlIO_list_alloc(aTHX);
    PerlIO_list_push(aTHX_ PL_known_layers, tab, NULL);
    PerlIO_debug("define %s %p\n", tab->name, (void*)tab);
}

int
PerlIO_parse_layers(pTHX_ PerlIO_list_t *av, const char *names)
{
    dVAR;
    if (names) {
	const char *s = names;
	while (*s) {
	    while (isSPACE(*s) || *s == ':')
		s++;
	    if (*s) {
		STRLEN llen = 0;
		const char *e = s;
		const char *as = NULL;
		STRLEN alen = 0;
		if (!isIDFIRST(*s)) {
		    /*
		     * Message is consistent with how attribute lists are
		     * passed. Even though this means "foo : : bar" is
		     * seen as an invalid separator character.
		     */
		    const char q = ((*s == '\'') ? '"' : '\'');
		    if (ckWARN(WARN_LAYER))
			Perl_warner(aTHX_ packWARN(WARN_LAYER),
			      "Invalid separator character %c%c%c in PerlIO layer specification %s",
			      q, *s, q, s);
		    SETERRNO(EINVAL, LIB_INVARG);
		    return -1;
		}
		do {
		    e++;
		} while (isALNUM(*e));
		llen = e - s;
		if (*e == '(') {
		    int nesting = 1;
		    as = ++e;
		    while (nesting) {
			switch (*e++) {
			case ')':
			    if (--nesting == 0)
				alen = (e - 1) - as;
			    break;
			case '(':
			    ++nesting;
			    break;
			case '\\':
			    /*
			     * It's a nul terminated string, not allowed
			     * to \ the terminating null. Anything other
			     * character is passed over.
			     */
			    if (*e++) {
				break;
			    }
			    /*
			     * Drop through
			     */
			case '\0':
			    e--;
			    if (ckWARN(WARN_LAYER))
				Perl_warner(aTHX_ packWARN(WARN_LAYER),
				      "Argument list not closed for PerlIO layer \"%.*s\"",
				      (int) (e - s), s);
			    return -1;
			default:
			    /*
			     * boring.
			     */
			    break;
			}
		    }
		}
		if (e > s) {
		    PerlIO_funcs * const layer =
			PerlIO_find_layer(aTHX_ s, llen, 1);
		    if (layer) {
			SV *arg = NULL;
			if (as)
			    arg = newSVpvn(as, alen);
			PerlIO_list_push(aTHX_ av, layer,
					 (arg) ? arg : &PL_sv_undef);
			if (arg)
			    SvREFCNT_dec(arg);
		    }
		    else {
			if (ckWARN(WARN_LAYER))
			    Perl_warner(aTHX_ packWARN(WARN_LAYER), "Unknown PerlIO layer \"%.*s\"",
				  (int) llen, s);
			return -1;
		    }
		}
		s = e;
	    }
	}
    }
    return 0;
}

void
PerlIO_default_buffer(pTHX_ PerlIO_list_t *av)
{
    dVAR;
    PERLIO_FUNCS_DECL(*tab) = &PerlIO_perlio;
#ifdef PERLIO_USING_CRLF
    tab = &PerlIO_crlf;
#else
    if (PerlIO_stdio.Set_ptrcnt)
	tab = &PerlIO_stdio;
#endif
    PerlIO_debug("Pushing %s\n", tab->name);
    PerlIO_list_push(aTHX_ av, PerlIO_find_layer(aTHX_ tab->name, 0, 0),
		     &PL_sv_undef);
}

SV *
PerlIO_arg_fetch(PerlIO_list_t *av, IV n)
{
    return av->array[n].arg;
}

PerlIO_funcs *
PerlIO_layer_fetch(pTHX_ PerlIO_list_t *av, IV n, PerlIO_funcs *def)
{
    if (n >= 0 && n < av->cur) {
	PerlIO_debug("Layer %" IVdf " is %s\n", n,
		     av->array[n].funcs->name);
	return av->array[n].funcs;
    }
    if (!def)
	Perl_croak(aTHX_ "panic: PerlIO layer array corrupt");
    return def;
}

IV
PerlIOPop_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    PERL_UNUSED_ARG(mode);
    PERL_UNUSED_ARG(arg);
    PERL_UNUSED_ARG(tab);
    if (PerlIOValid(f)) {
	PerlIO_flush(f);
	PerlIO_pop(aTHX_ f);
	return 0;
    }
    return -1;
}

PERLIO_FUNCS_DECL(PerlIO_remove) = {
    sizeof(PerlIO_funcs),
    "pop",
    0,
    PERLIO_K_DUMMY | PERLIO_K_UTF8,
    PerlIOPop_pushed,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* flush */
    NULL,                       /* fill */
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* get_base */
    NULL,                       /* get_bufsiz */
    NULL,                       /* get_ptr */
    NULL,                       /* get_cnt */
    NULL,                       /* set_ptrcnt */
};

PerlIO_list_t *
PerlIO_default_layers(pTHX)
{
    dVAR;
    if (!PL_def_layerlist) {
	const char * const s = (PL_tainting) ? NULL : PerlEnv_getenv("PERLIO");
	PERLIO_FUNCS_DECL(*osLayer) = &PerlIO_unix;
	PL_def_layerlist = PerlIO_list_alloc(aTHX);
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_unix));
#if defined(WIN32)
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_win32));
#if 0
	osLayer = &PerlIO_win32;
#endif
#endif
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_raw));
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_perlio));
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_stdio));
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_crlf));
#ifdef HAS_MMAP
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_mmap));
#endif
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_utf8));
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_remove));
	PerlIO_define_layer(aTHX_ PERLIO_FUNCS_CAST(&PerlIO_byte));
	PerlIO_list_push(aTHX_ PL_def_layerlist,
			 PerlIO_find_layer(aTHX_ osLayer->name, 0, 0),
			 &PL_sv_undef);
	if (s) {
	    PerlIO_parse_layers(aTHX_ PL_def_layerlist, s);
	}
	else {
	    PerlIO_default_buffer(aTHX_ PL_def_layerlist);
	}
    }
    if (PL_def_layerlist->cur < 2) {
	PerlIO_default_buffer(aTHX_ PL_def_layerlist);
    }
    return PL_def_layerlist;
}

void
Perl_boot_core_PerlIO(pTHX)
{
#ifdef USE_ATTRIBUTES_FOR_PERLIO
    newXS("io::MODIFY_SCALAR_ATTRIBUTES", XS_io_MODIFY_SCALAR_ATTRIBUTES,
	  __FILE__);
#endif
    newXS("PerlIO::Layer::find", XS_PerlIO__Layer__find, __FILE__);
    newXS("PerlIO::Layer::NoWarnings", XS_PerlIO__Layer__NoWarnings, __FILE__);
}

PerlIO_funcs *
PerlIO_default_layer(pTHX_ I32 n)
{
    dVAR;
    PerlIO_list_t * const av = PerlIO_default_layers(aTHX);
    if (n < 0)
	n += av->cur;
    return PerlIO_layer_fetch(aTHX_ av, n, PERLIO_FUNCS_CAST(&PerlIO_stdio));
}

#define PerlIO_default_top() PerlIO_default_layer(aTHX_ -1)
#define PerlIO_default_btm() PerlIO_default_layer(aTHX_ 0)

void
PerlIO_stdstreams(pTHX)
{
    dVAR;
    if (!PL_perlio) {
	PerlIO_allocate(aTHX);
	PerlIO_fdopen(0, "Ir" PERLIO_STDTEXT);
	PerlIO_fdopen(1, "Iw" PERLIO_STDTEXT);
	PerlIO_fdopen(2, "Iw" PERLIO_STDTEXT);
    }
}

PerlIO *
PerlIO_push(pTHX_ PerlIO *f, PERLIO_FUNCS_DECL(*tab), const char *mode, SV *arg)
{
    if (tab->fsize != sizeof(PerlIO_funcs)) {
      mismatch:
	Perl_croak(aTHX_ "Layer does not match this perl");
    }
    if (tab->size) {
	PerlIOl *l;
	if (tab->size < sizeof(PerlIOl)) {
	    goto mismatch;
	}
	/* Real layer with a data area */
	if (f) {
	    char *temp;
	    Newxz(temp, tab->size, char);
	    l = (PerlIOl*)temp;
	    if (l) {
		l->next = *f;
		l->tab = (PerlIO_funcs*) tab;
		*f = l;
		PerlIO_debug("PerlIO_push f=%p %s %s %p\n",
			     (void*)f, tab->name,
			     (mode) ? mode : "(Null)", (void*)arg);
		if (*l->tab->Pushed &&
		    (*l->tab->Pushed)
		      (aTHX_ f, mode, arg, (PerlIO_funcs*) tab) != 0) {
		    PerlIO_pop(aTHX_ f);
		    return NULL;
		}
	    }
	    else
		return NULL;
	}
    }
    else if (f) {
	/* Pseudo-layer where push does its own stack adjust */
	PerlIO_debug("PerlIO_push f=%p %s %s %p\n", (void*)f, tab->name,
		     (mode) ? mode : "(Null)", (void*)arg);
	if (tab->Pushed &&
	    (*tab->Pushed) (aTHX_ f, mode, arg, (PerlIO_funcs*) tab) != 0) {
	     return NULL;
	}
    }
    return f;
}

IV
PerlIOBase_binmode(pTHX_ PerlIO *f)
{
   if (PerlIOValid(f)) {
	/* Is layer suitable for raw stream ? */
	if (PerlIOBase(f)->tab->kind & PERLIO_K_RAW) {
	    /* Yes - turn off UTF-8-ness, to undo UTF-8 locale effects */
	    PerlIOBase(f)->flags &= ~PERLIO_F_UTF8;
	}
	else {
	    /* Not suitable - pop it */
	    PerlIO_pop(aTHX_ f);
	}
	return 0;
   }
   return -1;
}

IV
PerlIORaw_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    PERL_UNUSED_ARG(mode);
    PERL_UNUSED_ARG(arg);
    PERL_UNUSED_ARG(tab);

    if (PerlIOValid(f)) {
	PerlIO *t;
	const PerlIOl *l;
	PerlIO_flush(f);
	/*
	 * Strip all layers that are not suitable for a raw stream
	 */
	t = f;
	while (t && (l = *t)) {
	    if (l->tab->Binmode) {
		/* Has a handler - normal case */
		if ((*l->tab->Binmode)(aTHX_ f) == 0) {
		    if (*t == l) {
			/* Layer still there - move down a layer */
			t = PerlIONext(t);
		    }
		}
		else {
		    return -1;
		}
	    }
	    else {
		/* No handler - pop it */
		PerlIO_pop(aTHX_ t);
	    }
	}
	if (PerlIOValid(f)) {
	    PerlIO_debug(":raw f=%p :%s\n", (void*)f, PerlIOBase(f)->tab->name);
	    return 0;
	}
    }
    return -1;
}

int
PerlIO_apply_layera(pTHX_ PerlIO *f, const char *mode,
		    PerlIO_list_t *layers, IV n, IV max)
{
    int code = 0;
    while (n < max) {
	PerlIO_funcs * const tab = PerlIO_layer_fetch(aTHX_ layers, n, NULL);
	if (tab) {
	    if (!PerlIO_push(aTHX_ f, tab, mode, PerlIOArg)) {
		code = -1;
		break;
	    }
	}
	n++;
    }
    return code;
}

int
PerlIO_apply_layers(pTHX_ PerlIO *f, const char *mode, const char *names)
{
    int code = 0;
    if (f && names) {
	PerlIO_list_t * const layers = PerlIO_list_alloc(aTHX);
	code = PerlIO_parse_layers(aTHX_ layers, names);
	if (code == 0) {
	    code = PerlIO_apply_layera(aTHX_ f, mode, layers, 0, layers->cur);
	}
	PerlIO_list_free(aTHX_ layers);
    }
    return code;
}


/*--------------------------------------------------------------------------------------*/
/*
 * Given the abstraction above the public API functions
 */

int
PerlIO_binmode(pTHX_ PerlIO *f, int iotype, int mode, const char *names)
{
    PerlIO_debug("PerlIO_binmode f=%p %s %c %x %s\n", (void*)f,
                 (PerlIOBase(f)) ? PerlIOBase(f)->tab->name : "(Null)",
                 iotype, mode, (names) ? names : "(Null)");

    if (names) {
	/* Do not flush etc. if (e.g.) switching encodings.
	   if a pushed layer knows it needs to flush lower layers
	   (for example :unix which is never going to call them)
	   it can do the flush when it is pushed.
	 */
	return PerlIO_apply_layers(aTHX_ f, NULL, names) == 0 ? TRUE : FALSE;
    }
    else {
	/* Fake 5.6 legacy of using this call to turn ON O_TEXT */
#ifdef PERLIO_USING_CRLF
	/* Legacy binmode only has meaning if O_TEXT has a value distinct from
	   O_BINARY so we can look for it in mode.
	 */
	if (!(mode & O_BINARY)) {
	    /* Text mode */
	    /* FIXME?: Looking down the layer stack seems wrong,
	       but is a way of reaching past (say) an encoding layer
	       to flip CRLF-ness of the layer(s) below
	     */
	    while (*f) {
		/* Perhaps we should turn on bottom-most aware layer
		   e.g. Ilya's idea that UNIX TTY could serve
		 */
		if (PerlIOBase(f)->tab->kind & PERLIO_K_CANCRLF) {
		    if (!(PerlIOBase(f)->flags & PERLIO_F_CRLF)) {
			/* Not in text mode - flush any pending stuff and flip it */
			PerlIO_flush(f);
			PerlIOBase(f)->flags |= PERLIO_F_CRLF;
		    }
		    /* Only need to turn it on in one layer so we are done */
		    return TRUE;
		}
		f = PerlIONext(f);
	    }
	    /* Not finding a CRLF aware layer presumably means we are binary
	       which is not what was requested - so we failed
	       We _could_ push :crlf layer but so could caller
	     */
	    return FALSE;
	}
#endif
	/* Legacy binmode is now _defined_ as being equivalent to pushing :raw
	   So code that used to be here is now in PerlIORaw_pushed().
	 */
	return PerlIO_push(aTHX_ f, PERLIO_FUNCS_CAST(&PerlIO_raw), NULL, NULL) ? TRUE : FALSE;
    }
}

int
PerlIO__close(pTHX_ PerlIO *f)
{
    if (PerlIOValid(f)) {
	PerlIO_funcs * const tab = PerlIOBase(f)->tab;
	if (tab && tab->Close)
	    return (*tab->Close)(aTHX_ f);
	else
	    return PerlIOBase_close(aTHX_ f);
    }
    else {
	SETERRNO(EBADF, SS_IVCHAN);
	return -1;
    }
}

int
Perl_PerlIO_close(pTHX_ PerlIO *f)
{
    const int code = PerlIO__close(aTHX_ f);
    while (PerlIOValid(f)) {
	PerlIO_pop(aTHX_ f);
    }
    return code;
}

int
Perl_PerlIO_fileno(pTHX_ PerlIO *f)
{
    dVAR;
     Perl_PerlIO_or_Base(f, Fileno, fileno, -1, (aTHX_ f));
}


static PerlIO_funcs *
PerlIO_layer_from_ref(pTHX_ SV *sv)
{
    dVAR;
    /*
     * For any scalar type load the handler which is bundled with perl
     */
    if (SvTYPE(sv) < SVt_PVAV) {
	PerlIO_funcs *f = PerlIO_find_layer(aTHX_ STR_WITH_LEN("scalar"), 1);
	/* This isn't supposed to happen, since PerlIO::scalar is core,
	 * but could happen anyway in smaller installs or with PAR */
	if (!f && ckWARN(WARN_LAYER))
	    Perl_warner(aTHX_ packWARN(WARN_LAYER), "Unknown PerlIO layer \"scalar\"");
	return f;
    }

    /*
     * For other types allow if layer is known but don't try and load it
     */
    switch (SvTYPE(sv)) {
    case SVt_PVAV:
	return PerlIO_find_layer(aTHX_ STR_WITH_LEN("Array"), 0);
    case SVt_PVHV:
	return PerlIO_find_layer(aTHX_ STR_WITH_LEN("Hash"), 0);
    case SVt_PVCV:
	return PerlIO_find_layer(aTHX_ STR_WITH_LEN("Code"), 0);
    case SVt_PVGV:
	return PerlIO_find_layer(aTHX_ STR_WITH_LEN("Glob"), 0);
    default:
	return NULL;
    }
}

PerlIO_list_t *
PerlIO_resolve_layers(pTHX_ const char *layers,
		      const char *mode, int narg, SV **args)
{
    dVAR;
    PerlIO_list_t *def = PerlIO_default_layers(aTHX);
    int incdef = 1;
    if (!PL_perlio)
	PerlIO_stdstreams(aTHX);
    if (narg) {
	SV * const arg = *args;
	/*
	 * If it is a reference but not an object see if we have a handler
	 * for it
	 */
	if (SvROK(arg) && !sv_isobject(arg)) {
	    PerlIO_funcs * const handler = PerlIO_layer_from_ref(aTHX_ SvRV(arg));
	    if (handler) {
		def = PerlIO_list_alloc(aTHX);
		PerlIO_list_push(aTHX_ def, handler, &PL_sv_undef);
		incdef = 0;
	    }
	    /*
	     * Don't fail if handler cannot be found :via(...) etc. may do
	     * something sensible else we will just stringfy and open
	     * resulting string.
	     */
	}
    }
    if (!layers || !*layers)
	layers = Perl_PerlIO_context_layers(aTHX_ mode);
    if (layers && *layers) {
	PerlIO_list_t *av;
	if (incdef) {
	    av = PerlIO_clone_list(aTHX_ def, NULL);
	}
	else {
	    av = def;
	}
	if (PerlIO_parse_layers(aTHX_ av, layers) == 0) {
	     return av;
	}
	else {
	    PerlIO_list_free(aTHX_ av);
	    return NULL;
	}
    }
    else {
	if (incdef)
	    def->refcnt++;
	return def;
    }
}

PerlIO *
PerlIO_openn(pTHX_ const char *layers, const char *mode, int fd,
	     int imode, int perm, PerlIO *f, int narg, SV **args)
{
    dVAR;
    if (!f && narg == 1 && *args == &PL_sv_undef) {
	if ((f = PerlIO_tmpfile())) {
	    if (!layers || !*layers)
		layers = Perl_PerlIO_context_layers(aTHX_ mode);
	    if (layers && *layers)
		PerlIO_apply_layers(aTHX_ f, mode, layers);
	}
    }
    else {
	PerlIO_list_t *layera;
	IV n;
	PerlIO_funcs *tab = NULL;
	if (PerlIOValid(f)) {
	    /*
	     * This is "reopen" - it is not tested as perl does not use it
	     * yet
	     */
	    PerlIOl *l = *f;
	    layera = PerlIO_list_alloc(aTHX);
	    while (l) {
		SV *arg = NULL;
		if (l->tab->Getarg)
		    arg = (*l->tab->Getarg) (aTHX_ &l, NULL, 0);
		PerlIO_list_push(aTHX_ layera, l->tab,
				 (arg) ? arg : &PL_sv_undef);
		if (arg)
		    SvREFCNT_dec(arg);
		l = *PerlIONext(&l);
	    }
	}
	else {
	    layera = PerlIO_resolve_layers(aTHX_ layers, mode, narg, args);
	    if (!layera) {
		return NULL;
	    }
	}
	/*
	 * Start at "top" of layer stack
	 */
	n = layera->cur - 1;
	while (n >= 0) {
	    PerlIO_funcs * const t = PerlIO_layer_fetch(aTHX_ layera, n, NULL);
	    if (t && t->Open) {
		tab = t;
		break;
	    }
	    n--;
	}
	if (tab) {
	    /*
	     * Found that layer 'n' can do opens - call it
	     */
	    if (narg > 1 && !(tab->kind & PERLIO_K_MULTIARG)) {
		Perl_croak(aTHX_ "More than one argument to open(,':%s')",tab->name);
	    }
	    PerlIO_debug("openn(%s,'%s','%s',%d,%x,%o,%p,%d,%p)\n",
			 tab->name, layers ? layers : "(Null)", mode, fd,
			 imode, perm, (void*)f, narg, (void*)args);
	    if (tab->Open)
		 f = (*tab->Open) (aTHX_ tab, layera, n, mode, fd, imode, perm,
				   f, narg, args);
	    else {
		 SETERRNO(EINVAL, LIB_INVARG);
		 f = NULL;
	    }
	    if (f) {
		if (n + 1 < layera->cur) {
		    /*
		     * More layers above the one that we used to open -
		     * apply them now
		     */
		    if (PerlIO_apply_layera(aTHX_ f, mode, layera, n + 1, layera->cur) != 0) {
			/* If pushing layers fails close the file */
			PerlIO_close(f);
			f = NULL;
		    }
		}
	    }
	}
	PerlIO_list_free(aTHX_ layera);
    }
    return f;
}


SSize_t
Perl_PerlIO_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
{
     Perl_PerlIO_or_Base(f, Read, read, -1, (aTHX_ f, vbuf, count));
}

SSize_t
Perl_PerlIO_unread(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
     Perl_PerlIO_or_Base(f, Unread, unread, -1, (aTHX_ f, vbuf, count));
}

SSize_t
Perl_PerlIO_write(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
     Perl_PerlIO_or_fail(f, Write, -1, (aTHX_ f, vbuf, count));
}

int
Perl_PerlIO_seek(pTHX_ PerlIO *f, Off_t offset, int whence)
{
     Perl_PerlIO_or_fail(f, Seek, -1, (aTHX_ f, offset, whence));
}

Off_t
Perl_PerlIO_tell(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_fail(f, Tell, -1, (aTHX_ f));
}

int
Perl_PerlIO_flush(pTHX_ PerlIO *f)
{
    dVAR;
    if (f) {
	if (*f) {
	    const PerlIO_funcs *tab = PerlIOBase(f)->tab;

	    if (tab && tab->Flush)
		return (*tab->Flush) (aTHX_ f);
	    else
		 return 0; /* If no Flush defined, silently succeed. */
	}
	else {
	    PerlIO_debug("Cannot flush f=%p\n", (void*)f);
	    SETERRNO(EBADF, SS_IVCHAN);
	    return -1;
	}
    }
    else {
	/*
	 * Is it good API design to do flush-all on NULL, a potentially
	 * errorneous input? Maybe some magical value (PerlIO*
	 * PERLIO_FLUSH_ALL = (PerlIO*)-1;)? Yes, stdio does similar
	 * things on fflush(NULL), but should we be bound by their design
	 * decisions? --jhi
	 */
	PerlIO **table = &PL_perlio;
	int code = 0;
	while ((f = *table)) {
	    int i;
	    table = (PerlIO **) (f++);
	    for (i = 1; i < PERLIO_TABLE_SIZE; i++) {
		if (*f && PerlIO_flush(f) != 0)
		    code = -1;
		f++;
	    }
	}
	return code;
    }
}

void
PerlIOBase_flush_linebuf(pTHX)
{
    dVAR;
    PerlIO **table = &PL_perlio;
    PerlIO *f;
    while ((f = *table)) {
	int i;
	table = (PerlIO **) (f++);
	for (i = 1; i < PERLIO_TABLE_SIZE; i++) {
	    if (*f
		&& (PerlIOBase(f)->
		    flags & (PERLIO_F_LINEBUF | PERLIO_F_CANWRITE))
		== (PERLIO_F_LINEBUF | PERLIO_F_CANWRITE))
		PerlIO_flush(f);
	    f++;
	}
    }
}

int
Perl_PerlIO_fill(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_fail(f, Fill, -1, (aTHX_ f));
}

int
PerlIO_isutf8(PerlIO *f)
{
     if (PerlIOValid(f))
	  return (PerlIOBase(f)->flags & PERLIO_F_UTF8) != 0;
     else
	  SETERRNO(EBADF, SS_IVCHAN);

     return -1;
}

int
Perl_PerlIO_eof(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_Base(f, Eof, eof, -1, (aTHX_ f));
}

int
Perl_PerlIO_error(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_Base(f, Error, error, -1, (aTHX_ f));
}

void
Perl_PerlIO_clearerr(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_Base_void(f, Clearerr, clearerr, (aTHX_ f));
}

void
Perl_PerlIO_setlinebuf(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_Base_void(f, Setlinebuf, setlinebuf, (aTHX_ f));
}

int
PerlIO_has_base(PerlIO *f)
{
     if (PerlIOValid(f)) {
	  const PerlIO_funcs * const tab = PerlIOBase(f)->tab;

	  if (tab)
	       return (tab->Get_base != NULL);
	  SETERRNO(EINVAL, LIB_INVARG);
     }
     else
	  SETERRNO(EBADF, SS_IVCHAN);

     return 0;
}

int
PerlIO_fast_gets(PerlIO *f)
{
    if (PerlIOValid(f) && (PerlIOBase(f)->flags & PERLIO_F_FASTGETS)) {
	 const PerlIO_funcs * const tab = PerlIOBase(f)->tab;

	 if (tab)
	      return (tab->Set_ptrcnt != NULL);
	 SETERRNO(EINVAL, LIB_INVARG);
    }
    else
	 SETERRNO(EBADF, SS_IVCHAN);

    return 0;
}

int
PerlIO_has_cntptr(PerlIO *f)
{
    if (PerlIOValid(f)) {
	const PerlIO_funcs * const tab = PerlIOBase(f)->tab;

	if (tab)
	     return (tab->Get_ptr != NULL && tab->Get_cnt != NULL);
	  SETERRNO(EINVAL, LIB_INVARG);
    }
    else
	 SETERRNO(EBADF, SS_IVCHAN);

    return 0;
}

int
PerlIO_canset_cnt(PerlIO *f)
{
    if (PerlIOValid(f)) {
	  const PerlIO_funcs * const tab = PerlIOBase(f)->tab;

	  if (tab)
	       return (tab->Set_ptrcnt != NULL);
	  SETERRNO(EINVAL, LIB_INVARG);
    }
    else
	 SETERRNO(EBADF, SS_IVCHAN);

    return 0;
}

STDCHAR *
Perl_PerlIO_get_base(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_fail(f, Get_base, NULL, (aTHX_ f));
}

int
Perl_PerlIO_get_bufsiz(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_fail(f, Get_bufsiz, -1, (aTHX_ f));
}

STDCHAR *
Perl_PerlIO_get_ptr(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_fail(f, Get_ptr, NULL, (aTHX_ f));
}

int
Perl_PerlIO_get_cnt(pTHX_ PerlIO *f)
{
     Perl_PerlIO_or_fail(f, Get_cnt, -1, (aTHX_ f));
}

void
Perl_PerlIO_set_cnt(pTHX_ PerlIO *f, int cnt)
{
     Perl_PerlIO_or_fail_void(f, Set_ptrcnt, (aTHX_ f, NULL, cnt));
}

void
Perl_PerlIO_set_ptrcnt(pTHX_ PerlIO *f, STDCHAR * ptr, int cnt)
{
     Perl_PerlIO_or_fail_void(f, Set_ptrcnt, (aTHX_ f, ptr, cnt));
}


/*--------------------------------------------------------------------------------------*/
/*
 * utf8 and raw dummy layers
 */

IV
PerlIOUtf8_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(mode);
    PERL_UNUSED_ARG(arg);
    if (PerlIOValid(f)) {
	if (tab->kind & PERLIO_K_UTF8)
	    PerlIOBase(f)->flags |= PERLIO_F_UTF8;
	else
	    PerlIOBase(f)->flags &= ~PERLIO_F_UTF8;
	return 0;
    }
    return -1;
}

PERLIO_FUNCS_DECL(PerlIO_utf8) = {
    sizeof(PerlIO_funcs),
    "utf8",
    0,
    PERLIO_K_DUMMY | PERLIO_K_UTF8,
    PerlIOUtf8_pushed,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* flush */
    NULL,                       /* fill */
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* get_base */
    NULL,                       /* get_bufsiz */
    NULL,                       /* get_ptr */
    NULL,                       /* get_cnt */
    NULL,                       /* set_ptrcnt */
};

PERLIO_FUNCS_DECL(PerlIO_byte) = {
    sizeof(PerlIO_funcs),
    "bytes",
    0,
    PERLIO_K_DUMMY,
    PerlIOUtf8_pushed,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* flush */
    NULL,                       /* fill */
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* get_base */
    NULL,                       /* get_bufsiz */
    NULL,                       /* get_ptr */
    NULL,                       /* get_cnt */
    NULL,                       /* set_ptrcnt */
};

PerlIO *
PerlIORaw_open(pTHX_ PerlIO_funcs *self, PerlIO_list_t *layers,
	       IV n, const char *mode, int fd, int imode, int perm,
	       PerlIO *old, int narg, SV **args)
{
    PerlIO_funcs * const tab = PerlIO_default_btm();
    PERL_UNUSED_ARG(self);
    if (tab && tab->Open)
	 return (*tab->Open) (aTHX_ tab, layers, n - 1, mode, fd, imode, perm,
			      old, narg, args);
    SETERRNO(EINVAL, LIB_INVARG);
    return NULL;
}

PERLIO_FUNCS_DECL(PerlIO_raw) = {
    sizeof(PerlIO_funcs),
    "raw",
    0,
    PERLIO_K_DUMMY,
    PerlIORaw_pushed,
    PerlIOBase_popped,
    PerlIORaw_open,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* flush */
    NULL,                       /* fill */
    NULL,
    NULL,
    NULL,
    NULL,
    NULL,                       /* get_base */
    NULL,                       /* get_bufsiz */
    NULL,                       /* get_ptr */
    NULL,                       /* get_cnt */
    NULL,                       /* set_ptrcnt */
};
/*--------------------------------------------------------------------------------------*/
/*--------------------------------------------------------------------------------------*/
/*
 * "Methods" of the "base class"
 */

IV
PerlIOBase_fileno(pTHX_ PerlIO *f)
{
    return PerlIOValid(f) ? PerlIO_fileno(PerlIONext(f)) : -1;
}

char *
PerlIO_modestr(PerlIO * f, char *buf)
{
    char *s = buf;
    if (PerlIOValid(f)) {
	const IV flags = PerlIOBase(f)->flags;
	if (flags & PERLIO_F_APPEND) {
	    *s++ = 'a';
	    if (flags & PERLIO_F_CANREAD) {
		*s++ = '+';
	    }
	}
	else if (flags & PERLIO_F_CANREAD) {
	    *s++ = 'r';
	    if (flags & PERLIO_F_CANWRITE)
		*s++ = '+';
	}
	else if (flags & PERLIO_F_CANWRITE) {
	    *s++ = 'w';
	    if (flags & PERLIO_F_CANREAD) {
		*s++ = '+';
	    }
	}
#ifdef PERLIO_USING_CRLF
	if (!(flags & PERLIO_F_CRLF))
	    *s++ = 'b';
#endif
    }
    *s = '\0';
    return buf;
}


IV
PerlIOBase_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    PerlIOl * const l = PerlIOBase(f);
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(arg);

    l->flags &= ~(PERLIO_F_CANREAD | PERLIO_F_CANWRITE |
		  PERLIO_F_TRUNCATE | PERLIO_F_APPEND);
    if (tab->Set_ptrcnt != NULL)
	l->flags |= PERLIO_F_FASTGETS;
    if (mode) {
	if (*mode == IoTYPE_NUMERIC || *mode == IoTYPE_IMPLICIT)
	    mode++;
	switch (*mode++) {
	case 'r':
	    l->flags |= PERLIO_F_CANREAD;
	    break;
	case 'a':
	    l->flags |= PERLIO_F_APPEND | PERLIO_F_CANWRITE;
	    break;
	case 'w':
	    l->flags |= PERLIO_F_TRUNCATE | PERLIO_F_CANWRITE;
	    break;
	default:
	    SETERRNO(EINVAL, LIB_INVARG);
	    return -1;
	}
	while (*mode) {
	    switch (*mode++) {
	    case '+':
		l->flags |= PERLIO_F_CANREAD | PERLIO_F_CANWRITE;
		break;
	    case 'b':
		l->flags &= ~PERLIO_F_CRLF;
		break;
	    case 't':
		l->flags |= PERLIO_F_CRLF;
		break;
	    default:
		SETERRNO(EINVAL, LIB_INVARG);
		return -1;
	    }
	}
    }
    else {
	if (l->next) {
	    l->flags |= l->next->flags &
		(PERLIO_F_CANREAD | PERLIO_F_CANWRITE | PERLIO_F_TRUNCATE |
		 PERLIO_F_APPEND);
	}
    }
#if 0
    PerlIO_debug("PerlIOBase_pushed f=%p %s %s fl=%08" UVxf " (%s)\n",
		 (void*)f, PerlIOBase(f)->tab->name, (omode) ? omode : "(Null)",
		 l->flags, PerlIO_modestr(f, temp));
#endif
    return 0;
}

IV
PerlIOBase_popped(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(f);
    return 0;
}

SSize_t
PerlIOBase_unread(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    /*
     * Save the position as current head considers it
     */
    const Off_t old = PerlIO_tell(f);
    PerlIO_push(aTHX_ f, PERLIO_FUNCS_CAST(&PerlIO_pending), "r", NULL);
    PerlIOSelf(f, PerlIOBuf)->posn = old;
    return PerlIOBuf_unread(aTHX_ f, vbuf, count);
}

SSize_t
PerlIOBase_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
{
    STDCHAR *buf = (STDCHAR *) vbuf;
    if (f) {
        if (!(PerlIOBase(f)->flags & PERLIO_F_CANREAD)) {
	    PerlIOBase(f)->flags |= PERLIO_F_ERROR;
	    SETERRNO(EBADF, SS_IVCHAN);
	    return 0;
	}
	while (count > 0) {
	 get_cnt:
	  {
	    SSize_t avail = PerlIO_get_cnt(f);
	    SSize_t take = 0;
	    if (avail > 0)
		take = ((SSize_t)count < avail) ? (SSize_t)count : avail;
	    if (take > 0) {
		STDCHAR *ptr = PerlIO_get_ptr(f);
		Copy(ptr, buf, take, STDCHAR);
		PerlIO_set_ptrcnt(f, ptr + take, (avail -= take));
		count -= take;
		buf += take;
		if (avail == 0)		/* set_ptrcnt could have reset avail */
		    goto get_cnt;
	    }
	    if (count > 0 && avail <= 0) {
		if (PerlIO_fill(f) != 0)
		    break;
	    }
	  }
	}
	return (buf - (STDCHAR *) vbuf);
    }
    return 0;
}

IV
PerlIOBase_noop_ok(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(f);
    return 0;
}

IV
PerlIOBase_noop_fail(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;
    PERL_UNUSED_ARG(f);
    return -1;
}

IV
PerlIOBase_close(pTHX_ PerlIO *f)
{
    IV code = -1;
    if (PerlIOValid(f)) {
	PerlIO *n = PerlIONext(f);
	code = PerlIO_flush(f);
	PerlIOBase(f)->flags &=
	   ~(PERLIO_F_CANREAD | PERLIO_F_CANWRITE | PERLIO_F_OPEN);
	while (PerlIOValid(n)) {
	    const PerlIO_funcs * const tab = PerlIOBase(n)->tab;
	    if (tab && tab->Close) {
		if ((*tab->Close)(aTHX_ n) != 0)
		    code = -1;
		break;
	    }
	    else {
		PerlIOBase(n)->flags &=
		    ~(PERLIO_F_CANREAD | PERLIO_F_CANWRITE | PERLIO_F_OPEN);
	    }
	    n = PerlIONext(n);
	}
    }
    else {
	SETERRNO(EBADF, SS_IVCHAN);
    }
    return code;
}

IV
PerlIOBase_eof(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;
    if (PerlIOValid(f)) {
	return (PerlIOBase(f)->flags & PERLIO_F_EOF) != 0;
    }
    return 1;
}

IV
PerlIOBase_error(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;
    if (PerlIOValid(f)) {
	return (PerlIOBase(f)->flags & PERLIO_F_ERROR) != 0;
    }
    return 1;
}

void
PerlIOBase_clearerr(pTHX_ PerlIO *f)
{
    if (PerlIOValid(f)) {
	PerlIO * const n = PerlIONext(f);
	PerlIOBase(f)->flags &= ~(PERLIO_F_ERROR | PERLIO_F_EOF);
	if (PerlIOValid(n))
	    PerlIO_clearerr(n);
    }
}

void
PerlIOBase_setlinebuf(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;
    if (PerlIOValid(f)) {
	PerlIOBase(f)->flags |= PERLIO_F_LINEBUF;
    }
}

SV *
PerlIO_sv_dup(pTHX_ SV *arg, CLONE_PARAMS *param)
{
    if (!arg)
	return NULL;
#ifdef sv_dup
    if (param) {
	arg = sv_dup(arg, param);
	SvREFCNT_inc_simple_void_NN(arg);
	return arg;
    }
    else {
	return newSVsv(arg);
    }
#else
    PERL_UNUSED_ARG(param);
    return newSVsv(arg);
#endif
}

PerlIO *
PerlIOBase_dup(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags)
{
    PerlIO * const nexto = PerlIONext(o);
    if (PerlIOValid(nexto)) {
	const PerlIO_funcs * const tab = PerlIOBase(nexto)->tab;
	if (tab && tab->Dup)
	    f = (*tab->Dup)(aTHX_ f, nexto, param, flags);
	else
	    f = PerlIOBase_dup(aTHX_ f, nexto, param, flags);
    }
    if (f) {
	PerlIO_funcs * const self = PerlIOBase(o)->tab;
	SV *arg = NULL;
	char buf[8];
	PerlIO_debug("PerlIOBase_dup %s f=%p o=%p param=%p\n",
		     self->name, (void*)f, (void*)o, (void*)param);
	if (self->Getarg)
	    arg = (*self->Getarg)(aTHX_ o, param, flags);
	f = PerlIO_push(aTHX_ f, self, PerlIO_modestr(o,buf), arg);
	if (PerlIOBase(o)->flags & PERLIO_F_UTF8)
	    PerlIOBase(f)->flags |= PERLIO_F_UTF8;
	if (arg)
	    SvREFCNT_dec(arg);
    }
    return f;
}

/* PL_perlio_fd_refcnt[] is in intrpvar.h */

/* Must be called with PL_perlio_mutex locked. */
static void
S_more_refcounted_fds(pTHX_ const int new_fd) {
    dVAR;
    const int old_max = PL_perlio_fd_refcnt_size;
    const int new_max = 16 + (new_fd & ~15);
    int *new_array;

    PerlIO_debug("More fds - old=%d, need %d, new=%d\n",
		 old_max, new_fd, new_max);

    if (new_fd < old_max) {
	return;
    }

    assert (new_max > new_fd);

    /* Use plain realloc() since we need this memory to be really
     * global and visible to all the interpreters and/or threads. */
    new_array = (int*) realloc(PL_perlio_fd_refcnt, new_max * sizeof(int));

    if (!new_array) {
#ifdef USE_ITHREADS
	MUTEX_UNLOCK(&PL_perlio_mutex);
#endif
	/* Can't use PerlIO to write as it allocates memory */
	PerlLIO_write(PerlIO_fileno(Perl_error_log),
		      PL_no_mem, strlen(PL_no_mem));
	my_exit(1);
    }

    PL_perlio_fd_refcnt_size = new_max;
    PL_perlio_fd_refcnt = new_array;

    PerlIO_debug("Zeroing %p, %d\n",
		 (void*)(new_array + old_max),
		 new_max - old_max);

    Zero(new_array + old_max, new_max - old_max, int);
}


void
PerlIO_init(pTHX)
{
    /* MUTEX_INIT(&PL_perlio_mutex) is done in PERL_SYS_INIT3(). */
    PERL_UNUSED_CONTEXT;
}

void
PerlIOUnix_refcnt_inc(int fd)
{
    dTHX;
    if (fd >= 0) {
	dVAR;

#ifdef USE_ITHREADS
	MUTEX_LOCK(&PL_perlio_mutex);
#endif
	if (fd >= PL_perlio_fd_refcnt_size)
	    S_more_refcounted_fds(aTHX_ fd);

	PL_perlio_fd_refcnt[fd]++;
	if (PL_perlio_fd_refcnt[fd] <= 0) {
	    Perl_croak(aTHX_ "refcnt_inc: fd %d: %d <= 0\n",
		       fd, PL_perlio_fd_refcnt[fd]);
	}
	PerlIO_debug("refcnt_inc: fd %d refcnt=%d\n",
		     fd, PL_perlio_fd_refcnt[fd]);

#ifdef USE_ITHREADS
	MUTEX_UNLOCK(&PL_perlio_mutex);
#endif
    } else {
	Perl_croak(aTHX_ "refcnt_inc: fd %d < 0\n", fd);
    }
}

int
PerlIOUnix_refcnt_dec(int fd)
{
    dTHX;
    int cnt = 0;
    if (fd >= 0) {
	dVAR;
#ifdef USE_ITHREADS
	MUTEX_LOCK(&PL_perlio_mutex);
#endif
	if (fd >= PL_perlio_fd_refcnt_size) {
	    Perl_croak(aTHX_ "refcnt_dec: fd %d >= refcnt_size %d\n",
		       fd, PL_perlio_fd_refcnt_size);
	}
	if (PL_perlio_fd_refcnt[fd] <= 0) {
	    Perl_croak(aTHX_ "refcnt_dec: fd %d: %d <= 0\n",
		       fd, PL_perlio_fd_refcnt[fd]);
	}
	cnt = --PL_perlio_fd_refcnt[fd];
	PerlIO_debug("refcnt_dec: fd %d refcnt=%d\n", fd, cnt);
#ifdef USE_ITHREADS
	MUTEX_UNLOCK(&PL_perlio_mutex);
#endif
    } else {
	Perl_croak(aTHX_ "refcnt_dec: fd %d < 0\n", fd);
    }
    return cnt;
}

void
PerlIO_cleanup(pTHX)
{
    dVAR;
    int i;
#ifdef USE_ITHREADS
    PerlIO_debug("Cleanup layers for %p\n",(void*)aTHX);
#else
    PerlIO_debug("Cleanup layers\n");
#endif

    /* Raise STDIN..STDERR refcount so we don't close them */
    for (i=0; i < 3; i++)
	PerlIOUnix_refcnt_inc(i);
    PerlIO_cleantable(aTHX_ &PL_perlio);
    /* Restore STDIN..STDERR refcount */
    for (i=0; i < 3; i++)
	PerlIOUnix_refcnt_dec(i);

    if (PL_known_layers) {
	PerlIO_list_free(aTHX_ PL_known_layers);
	PL_known_layers = NULL;
    }
    if (PL_def_layerlist) {
	PerlIO_list_free(aTHX_ PL_def_layerlist);
	PL_def_layerlist = NULL;
    }
}

void PerlIO_teardown() /* Call only from PERL_SYS_TERM(). */
{
    dVAR;
#if 0
/* XXX we can't rely on an interpreter being present at this late stage,
   XXX so we can't use a function like PerlLIO_write that relies on one
   being present (at least in win32) :-(.
   Disable for now.
*/
#ifdef DEBUGGING
    {
	/* By now all filehandles should have been closed, so any
	 * stray (non-STD-)filehandles indicate *possible* (PerlIO)
	 * errors. */
#define PERLIO_TEARDOWN_MESSAGE_BUF_SIZE 64
#define PERLIO_TEARDOWN_MESSAGE_FD 2
	char buf[PERLIO_TEARDOWN_MESSAGE_BUF_SIZE];
	int i;
	for (i = 3; i < PL_perlio_fd_refcnt_size; i++) {
	    if (PL_perlio_fd_refcnt[i]) {
		const STRLEN len =
		    my_snprintf(buf, sizeof(buf),
				"PerlIO_teardown: fd %d refcnt=%d\n",
				i, PL_perlio_fd_refcnt[i]);
		PerlLIO_write(PERLIO_TEARDOWN_MESSAGE_FD, buf, len);
	    }
	}
    }
#endif
#endif
    /* Not bothering with PL_perlio_mutex since by now
     * all the interpreters are gone. */
    if (PL_perlio_fd_refcnt_size /* Assuming initial size of zero. */
        && PL_perlio_fd_refcnt) {
	free(PL_perlio_fd_refcnt); /* To match realloc() in S_more_refcounted_fds(). */
	PL_perlio_fd_refcnt = NULL;
	PL_perlio_fd_refcnt_size = 0;
    }
}

/*--------------------------------------------------------------------------------------*/
/*
 * Bottom-most level for UNIX-like case
 */

typedef struct {
    struct _PerlIO base;        /* The generic part */
    int fd;                     /* UNIX like file descriptor */
    int oflags;                 /* open/fcntl flags */
} PerlIOUnix;

int
PerlIOUnix_oflags(const char *mode)
{
    int oflags = -1;
    if (*mode == IoTYPE_IMPLICIT || *mode == IoTYPE_NUMERIC)
	mode++;
    switch (*mode) {
    case 'r':
	oflags = O_RDONLY;
	if (*++mode == '+') {
	    oflags = O_RDWR;
	    mode++;
	}
	break;

    case 'w':
	oflags = O_CREAT | O_TRUNC;
	if (*++mode == '+') {
	    oflags |= O_RDWR;
	    mode++;
	}
	else
	    oflags |= O_WRONLY;
	break;

    case 'a':
	oflags = O_CREAT | O_APPEND;
	if (*++mode == '+') {
	    oflags |= O_RDWR;
	    mode++;
	}
	else
	    oflags |= O_WRONLY;
	break;
    }
    if (*mode == 'b') {
	oflags |= O_BINARY;
	oflags &= ~O_TEXT;
	mode++;
    }
    else if (*mode == 't') {
	oflags |= O_TEXT;
	oflags &= ~O_BINARY;
	mode++;
    }
    /*
     * Always open in binary mode
     */
    oflags |= O_BINARY;
    if (*mode || oflags == -1) {
	SETERRNO(EINVAL, LIB_INVARG);
	oflags = -1;
    }
    return oflags;
}

IV
PerlIOUnix_fileno(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;
    return PerlIOSelf(f, PerlIOUnix)->fd;
}

static void
PerlIOUnix_setfd(pTHX_ PerlIO *f, int fd, int imode)
{
    PerlIOUnix * const s = PerlIOSelf(f, PerlIOUnix);
#if defined(WIN32)
    Stat_t st;
    if (PerlLIO_fstat(fd, &st) == 0) {
	if (!S_ISREG(st.st_mode)) {
	    PerlIO_debug("%d is not regular file\n",fd);
    	    PerlIOBase(f)->flags |= PERLIO_F_NOTREG;
	}
	else {
	    PerlIO_debug("%d _is_ a regular file\n",fd);
	}
    }
#endif
    s->fd = fd;
    s->oflags = imode;
    PerlIOUnix_refcnt_inc(fd);
    PERL_UNUSED_CONTEXT;
}

IV
PerlIOUnix_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    IV code = PerlIOBase_pushed(aTHX_ f, mode, arg, tab);
    if (*PerlIONext(f)) {
	/* We never call down so do any pending stuff now */
	PerlIO_flush(PerlIONext(f));
	/*
	 * XXX could (or should) we retrieve the oflags from the open file
	 * handle rather than believing the "mode" we are passed in? XXX
	 * Should the value on NULL mode be 0 or -1?
	 */
        PerlIOUnix_setfd(aTHX_ f, PerlIO_fileno(PerlIONext(f)),
                         mode ? PerlIOUnix_oflags(mode) : -1);
    }
    PerlIOBase(f)->flags |= PERLIO_F_OPEN;

    return code;
}

IV
PerlIOUnix_seek(pTHX_ PerlIO *f, Off_t offset, int whence)
{
    const int fd = PerlIOSelf(f, PerlIOUnix)->fd;
    Off_t new_loc;
    PERL_UNUSED_CONTEXT;
    if (PerlIOBase(f)->flags & PERLIO_F_NOTREG) {
#ifdef  ESPIPE
	SETERRNO(ESPIPE, LIB_INVARG);
#else
	SETERRNO(EINVAL, LIB_INVARG);
#endif
	return -1;
    }
    new_loc = PerlLIO_lseek(fd, offset, whence);
    if (new_loc == (Off_t) - 1)
	return -1;
    PerlIOBase(f)->flags &= ~PERLIO_F_EOF;
    return  0;
}

PerlIO *
PerlIOUnix_open(pTHX_ PerlIO_funcs *self, PerlIO_list_t *layers,
		IV n, const char *mode, int fd, int imode,
		int perm, PerlIO *f, int narg, SV **args)
{
    if (PerlIOValid(f)) {
	if (PerlIOBase(f)->flags & PERLIO_F_OPEN)
	    (*PerlIOBase(f)->tab->Close)(aTHX_ f);
    }
    if (narg > 0) {
	if (*mode == IoTYPE_NUMERIC)
	    mode++;
	else {
	    imode = PerlIOUnix_oflags(mode);
	    perm = 0666;
	}
	if (imode != -1) {
	    const char *path = SvPV_nolen_const(*args);
	    fd = PerlLIO_open3(path, imode, perm);
	}
    }
    if (fd >= 0) {
	if (*mode == IoTYPE_IMPLICIT)
	    mode++;
	if (!f) {
	    f = PerlIO_allocate(aTHX);
	}
	if (!PerlIOValid(f)) {
	    if (!(f = PerlIO_push(aTHX_ f, self, mode, PerlIOArg))) {
		return NULL;
	    }
	}
        PerlIOUnix_setfd(aTHX_ f, fd, imode);
	PerlIOBase(f)->flags |= PERLIO_F_OPEN;
	if (*mode == IoTYPE_APPEND)
	    PerlIOUnix_seek(aTHX_ f, 0, SEEK_END);
	return f;
    }
    else {
	if (f) {
	    NOOP;
	    /*
	     * FIXME: pop layers ???
	     */
	}
	return NULL;
    }
}

PerlIO *
PerlIOUnix_dup(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags)
{
    const PerlIOUnix * const os = PerlIOSelf(o, PerlIOUnix);
    int fd = os->fd;
    if (flags & PERLIO_DUP_FD) {
	fd = PerlLIO_dup(fd);
    }
    if (fd >= 0) {
	f = PerlIOBase_dup(aTHX_ f, o, param, flags);
	if (f) {
	    /* If all went well overwrite fd in dup'ed lay with the dup()'ed fd */
	    PerlIOUnix_setfd(aTHX_ f, fd, os->oflags);
	    return f;
	}
    }
    return NULL;
}


SSize_t
PerlIOUnix_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
{
    dVAR;
    const int fd = PerlIOSelf(f, PerlIOUnix)->fd;
#ifdef PERLIO_STD_SPECIAL
    if (fd == 0)
        return PERLIO_STD_IN(fd, vbuf, count);
#endif
    if (!(PerlIOBase(f)->flags & PERLIO_F_CANREAD) ||
         PerlIOBase(f)->flags & (PERLIO_F_EOF|PERLIO_F_ERROR)) {
	return 0;
    }
    while (1) {
	const SSize_t len = PerlLIO_read(fd, vbuf, count);
	if (len >= 0 || errno != EINTR) {
	    if (len < 0) {
		if (errno != EAGAIN) {
		    PerlIOBase(f)->flags |= PERLIO_F_ERROR;
		}
	    }
	    else if (len == 0 && count != 0) {
		PerlIOBase(f)->flags |= PERLIO_F_EOF;
		SETERRNO(0,0);
	    }
	    return len;
	}
	PERL_ASYNC_CHECK();
    }
    /*NOTREACHED*/
}

SSize_t
PerlIOUnix_write(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    dVAR;
    const int fd = PerlIOSelf(f, PerlIOUnix)->fd;
#ifdef PERLIO_STD_SPECIAL
    if (fd == 1 || fd == 2)
        return PERLIO_STD_OUT(fd, vbuf, count);
#endif
    while (1) {
	const SSize_t len = PerlLIO_write(fd, vbuf, count);
	if (len >= 0 || errno != EINTR) {
	    if (len < 0) {
		if (errno != EAGAIN) {
		    PerlIOBase(f)->flags |= PERLIO_F_ERROR;
		}
	    }
	    return len;
	}
	PERL_ASYNC_CHECK();
    }
    /*NOTREACHED*/
}

Off_t
PerlIOUnix_tell(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;

    return PerlLIO_lseek(PerlIOSelf(f, PerlIOUnix)->fd, 0, SEEK_CUR);
}


IV
PerlIOUnix_close(pTHX_ PerlIO *f)
{
    dVAR;
    const int fd = PerlIOSelf(f, PerlIOUnix)->fd;
    int code = 0;
    if (PerlIOBase(f)->flags & PERLIO_F_OPEN) {
	if (PerlIOUnix_refcnt_dec(fd) > 0) {
	    PerlIOBase(f)->flags &= ~PERLIO_F_OPEN;
	    return 0;
	}
    }
    else {
	SETERRNO(EBADF,SS_IVCHAN);
	return -1;
    }
    while (PerlLIO_close(fd) != 0) {
	if (errno != EINTR) {
	    code = -1;
	    break;
	}
	PERL_ASYNC_CHECK();
    }
    if (code == 0) {
	PerlIOBase(f)->flags &= ~PERLIO_F_OPEN;
    }
    return code;
}

PERLIO_FUNCS_DECL(PerlIO_unix) = {
    sizeof(PerlIO_funcs),
    "unix",
    sizeof(PerlIOUnix),
    PERLIO_K_RAW,
    PerlIOUnix_pushed,
    PerlIOBase_popped,
    PerlIOUnix_open,
    PerlIOBase_binmode,         /* binmode */
    NULL,
    PerlIOUnix_fileno,
    PerlIOUnix_dup,
    PerlIOUnix_read,
    PerlIOBase_unread,
    PerlIOUnix_write,
    PerlIOUnix_seek,
    PerlIOUnix_tell,
    PerlIOUnix_close,
    PerlIOBase_noop_ok,         /* flush */
    PerlIOBase_noop_fail,       /* fill */
    PerlIOBase_eof,
    PerlIOBase_error,
    PerlIOBase_clearerr,
    PerlIOBase_setlinebuf,
    NULL,                       /* get_base */
    NULL,                       /* get_bufsiz */
    NULL,                       /* get_ptr */
    NULL,                       /* get_cnt */
    NULL,                       /* set_ptrcnt */
};

/*--------------------------------------------------------------------------------------*/
/*
 * stdio as a layer
 */

#if defined(VMS) && !defined(STDIO_BUFFER_WRITABLE)
/* perl5.8 - This ensures the last minute VMS ungetc fix is not
   broken by the last second glibc 2.3 fix
 */
#define STDIO_BUFFER_WRITABLE
#endif


typedef struct {
    struct _PerlIO base;
    FILE *stdio;                /* The stream */
} PerlIOStdio;

IV
PerlIOStdio_fileno(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;

    if (PerlIOValid(f)) {
	FILE * const s = PerlIOSelf(f, PerlIOStdio)->stdio;
	if (s)
	    return PerlSIO_fileno(s);
    }
    errno = EBADF;
    return -1;
}

char *
PerlIOStdio_mode(const char *mode, char *tmode)
{
    char * const ret = tmode;
    if (mode) {
	while (*mode) {
	    *tmode++ = *mode++;
	}
    }
#if defined(PERLIO_USING_CRLF) || defined(__CYGWIN__)
    *tmode++ = 'b';
#endif
    *tmode = '\0';
    return ret;
}

IV
PerlIOStdio_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    PerlIO *n;
    if (PerlIOValid(f) && PerlIOValid(n = PerlIONext(f))) {
	PerlIO_funcs * const toptab = PerlIOBase(n)->tab;
        if (toptab == tab) {
	    /* Top is already stdio - pop self (duplicate) and use original */
	    PerlIO_pop(aTHX_ f);
	    return 0;
	} else {
	    const int fd = PerlIO_fileno(n);
	    char tmode[8];
	    FILE *stdio;
	    if (fd >= 0 && (stdio  = PerlSIO_fdopen(fd,
			    mode = PerlIOStdio_mode(mode, tmode)))) {
		PerlIOSelf(f, PerlIOStdio)->stdio = stdio;
	    	/* We never call down so do any pending stuff now */
	    	PerlIO_flush(PerlIONext(f));
	    }
	    else {
		return -1;
	    }
        }
    }
    return PerlIOBase_pushed(aTHX_ f, mode, arg, tab);
}


PerlIO *
PerlIO_importFILE(FILE *stdio, const char *mode)
{
    dTHX;
    PerlIO *f = NULL;
    if (stdio) {
	PerlIOStdio *s;
	if (!mode || !*mode) {
	    /* We need to probe to see how we can open the stream
	       so start with read/write and then try write and read
	       we dup() so that we can fclose without loosing the fd.

	       Note that the errno value set by a failing fdopen
	       varies between stdio implementations.
	     */
	    const int fd = PerlLIO_dup(fileno(stdio));
	    FILE *f2 = PerlSIO_fdopen(fd, (mode = "r+"));
	    if (!f2) {
		f2 = PerlSIO_fdopen(fd, (mode = "w"));
	    }
	    if (!f2) {
		f2 = PerlSIO_fdopen(fd, (mode = "r"));
	    }
	    if (!f2) {
		/* Don't seem to be able to open */
		PerlLIO_close(fd);
		return f;
	    }
	    fclose(f2);
	}
	if ((f = PerlIO_push(aTHX_(f = PerlIO_allocate(aTHX)), PERLIO_FUNCS_CAST(&PerlIO_stdio), mode, NULL))) {
	    s = PerlIOSelf(f, PerlIOStdio);
	    s->stdio = stdio;
	    PerlIOUnix_refcnt_inc(fileno(stdio));
	}
    }
    return f;
}

PerlIO *
PerlIOStdio_open(pTHX_ PerlIO_funcs *self, PerlIO_list_t *layers,
		 IV n, const char *mode, int fd, int imode,
		 int perm, PerlIO *f, int narg, SV **args)
{
    char tmode[8];
    if (PerlIOValid(f)) {
	const char * const path = SvPV_nolen_const(*args);
	PerlIOStdio * const s = PerlIOSelf(f, PerlIOStdio);
	FILE *stdio;
	PerlIOUnix_refcnt_dec(fileno(s->stdio));
	stdio = PerlSIO_freopen(path, (mode = PerlIOStdio_mode(mode, tmode)),
			    s->stdio);
	if (!s->stdio)
	    return NULL;
	s->stdio = stdio;
	PerlIOUnix_refcnt_inc(fileno(s->stdio));
	return f;
    }
    else {
	if (narg > 0) {
	    const char * const path = SvPV_nolen_const(*args);
	    if (*mode == IoTYPE_NUMERIC) {
		mode++;
		fd = PerlLIO_open3(path, imode, perm);
	    }
	    else {
	        FILE *stdio;
	        bool appended = FALSE;
#ifdef __CYGWIN__
		/* Cygwin wants its 'b' early. */
		appended = TRUE;
		mode = PerlIOStdio_mode(mode, tmode);
#endif
		stdio = PerlSIO_fopen(path, mode);
		if (stdio) {
		    if (!f) {
			f = PerlIO_allocate(aTHX);
		    }
		    if (!appended)
		        mode = PerlIOStdio_mode(mode, tmode);
		    f = PerlIO_push(aTHX_ f, self, mode, PerlIOArg);
		    if (f) {
			PerlIOSelf(f, PerlIOStdio)->stdio = stdio;
			PerlIOUnix_refcnt_inc(fileno(stdio));
		    } else {
			PerlSIO_fclose(stdio);
		    }
		    return f;
		}
		else {
		    return NULL;
		}
	    }
	}
	if (fd >= 0) {
	    FILE *stdio = NULL;
	    int init = 0;
	    if (*mode == IoTYPE_IMPLICIT) {
		init = 1;
		mode++;
	    }
	    if (init) {
		switch (fd) {
		case 0:
		    stdio = PerlSIO_stdin;
		    break;
		case 1:
		    stdio = PerlSIO_stdout;
		    break;
		case 2:
		    stdio = PerlSIO_stderr;
		    break;
		}
	    }
	    else {
		stdio = PerlSIO_fdopen(fd, mode =
				       PerlIOStdio_mode(mode, tmode));
	    }
	    if (stdio) {
		if (!f) {
		    f = PerlIO_allocate(aTHX);
		}
		if ((f = PerlIO_push(aTHX_ f, self, mode, PerlIOArg))) {
		    PerlIOSelf(f, PerlIOStdio)->stdio = stdio;
		    PerlIOUnix_refcnt_inc(fileno(stdio));
		}
		return f;
	    }
	}
    }
    return NULL;
}

PerlIO *
PerlIOStdio_dup(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags)
{
    /* This assumes no layers underneath - which is what
       happens, but is not how I remember it. NI-S 2001/10/16
     */
    if ((f = PerlIOBase_dup(aTHX_ f, o, param, flags))) {
	FILE *stdio = PerlIOSelf(o, PerlIOStdio)->stdio;
	const int fd = fileno(stdio);
	char mode[8];
	if (flags & PERLIO_DUP_FD) {
	    const int dfd = PerlLIO_dup(fileno(stdio));
	    if (dfd >= 0) {
		stdio = PerlSIO_fdopen(dfd, PerlIO_modestr(o,mode));
		goto set_this;
	    }
	    else {
		NOOP;
		/* FIXME: To avoid messy error recovery if dup fails
		   re-use the existing stdio as though flag was not set
		 */
	    }
	}
    	stdio = PerlSIO_fdopen(fd, PerlIO_modestr(o,mode));
    set_this:
	PerlIOSelf(f, PerlIOStdio)->stdio = stdio;
	PerlIOUnix_refcnt_inc(fileno(stdio));
    }
    return f;
}

static int
PerlIOStdio_invalidate_fileno(pTHX_ FILE *f)
{
    PERL_UNUSED_CONTEXT;

    /* XXX this could use PerlIO_canset_fileno() and
     * PerlIO_set_fileno() support from Configure
     */
#  if defined(__UCLIBC__)
    /* uClibc must come before glibc because it defines __GLIBC__ as well. */
    f->__filedes = -1;
    return 1;
#  elif defined(__GLIBC__)
    /* There may be a better way for GLIBC:
    	- libio.h defines a flag to not close() on cleanup
     */	
    f->_fileno = -1;
    return 1;
#  elif defined(__sun__)
    PERL_UNUSED_ARG(f);
    return 0;
#  elif defined(__hpux)
    f->__fileH = 0xff;
    f->__fileL = 0xff;
    return 1;
   /* Next one ->_file seems to be a reasonable fallback, i.e. if
      your platform does not have special entry try this one.
      [For OSF only have confirmation for Tru64 (alpha)
      but assume other OSFs will be similar.]
    */
#  elif defined(_AIX) || defined(__osf__) || defined(__irix__)
    f->_file = -1;
    return 1;
#  elif defined(__FreeBSD__)
    /* There may be a better way on FreeBSD:
        - we could insert a dummy func in the _close function entry
	f->_close = (int (*)(void *)) dummy_close;
     */
    f->_file = -1;
    return 1;
#  elif defined(__OpenBSD__)
    /* There may be a better way on OpenBSD:
        - we could insert a dummy func in the _close function entry
	f->_close = (int (*)(void *)) dummy_close;
     */
    f->_file = -1;
    return 1;
#  elif defined(__EMX__)
    /* f->_flags &= ~_IOOPEN; */	/* Will leak stream->_buffer */
    f->_handle = -1;
    return 1;
#  elif defined(__CYGWIN__)
    /* There may be a better way on CYGWIN:
        - we could insert a dummy func in the _close function entry
	f->_close = (int (*)(void *)) dummy_close;
     */
    f->_file = -1;
    return 1;
#  elif defined(WIN32)
#    if defined(__BORLANDC__)
    f->fd = PerlLIO_dup(fileno(f));
#    elif defined(UNDER_CE)
    /* WIN_CE does not have access to FILE internals, it hardly has FILE
       structure at all
     */
#    else
    f->_file = -1;
#    endif
    return 1;
#  else
#if 0
    /* Sarathy's code did this - we fall back to a dup/dup2 hack
       (which isn't thread safe) instead
     */
#    error "Don't know how to set FILE.fileno on your platform"
#endif
    PERL_UNUSED_ARG(f);
    return 0;
#  endif
}

IV
PerlIOStdio_close(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    if (!stdio) {
	errno = EBADF;
	return -1;
    }
    else {
        const int fd = fileno(stdio);
	int invalidate = 0;
	IV result = 0;
	int saveerr = 0;
	int dupfd = 0;
#ifdef SOCKS5_VERSION_NAME
    	/* Socks lib overrides close() but stdio isn't linked to
	   that library (though we are) - so we must call close()
	   on sockets on stdio's behalf.
	 */
    	int optval;
    	Sock_size_t optlen = sizeof(int);
	if (getsockopt(fd, SOL_SOCKET, SO_TYPE, (void *) &optval, &optlen) == 0)
	    invalidate = 1;
#endif
	if (PerlIOUnix_refcnt_dec(fd) > 0) /* File descriptor still in use */
	    invalidate = 1;
	if (invalidate) {
	    /* For STD* handles, don't close stdio, since we shared the FILE *, too. */
	    if (stdio == stdin) /* Some stdios are buggy fflush-ing inputs */
		return 0;
	    if (stdio == stdout || stdio == stderr)
		return PerlIO_flush(f);
            /* Tricky - must fclose(stdio) to free memory but not close(fd)
	       Use Sarathy's trick from maint-5.6 to invalidate the
	       fileno slot of the FILE *
	    */
	    result = PerlIO_flush(f);
	    saveerr = errno;
	    invalidate = PerlIOStdio_invalidate_fileno(aTHX_ stdio);
	    if (!invalidate)
		dupfd = PerlLIO_dup(fd);
	}
        result = PerlSIO_fclose(stdio);
	/* We treat error from stdio as success if we invalidated
	   errno may NOT be expected EBADF
	 */
	if (invalidate && result != 0) {
	    errno = saveerr;
	    result = 0;
	}
#ifdef SOCKS5_VERSION_NAME
	/* in SOCKS' case, let close() determine return value */
	result = close(fd);
#endif
	if (dupfd) {
	    PerlLIO_dup2(dupfd,fd);
	    PerlLIO_close(dupfd);
	}
	return result;
    }
}

SSize_t
PerlIOStdio_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
{
    dVAR;
    FILE * const s = PerlIOSelf(f, PerlIOStdio)->stdio;
    SSize_t got = 0;
    for (;;) {
	if (count == 1) {
	    STDCHAR *buf = (STDCHAR *) vbuf;
	    /*
	     * Perl is expecting PerlIO_getc() to fill the buffer Linux's
	     * stdio does not do that for fread()
	     */
	    const int ch = PerlSIO_fgetc(s);
	    if (ch != EOF) {
		*buf = ch;
		got = 1;
	    }
	}
	else
	    got = PerlSIO_fread(vbuf, 1, count, s);
	if (got == 0 && PerlSIO_ferror(s))
	    got = -1;
	if (got >= 0 || errno != EINTR)
	    break;
	PERL_ASYNC_CHECK();
	SETERRNO(0,0);	/* just in case */
    }
    return got;
}

SSize_t
PerlIOStdio_unread(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    SSize_t unread = 0;
    FILE * const s = PerlIOSelf(f, PerlIOStdio)->stdio;

#ifdef STDIO_BUFFER_WRITABLE
    if (PerlIO_fast_gets(f) && PerlIO_has_base(f)) {
	STDCHAR *buf = ((STDCHAR *) vbuf) + count;
	STDCHAR *base = PerlIO_get_base(f);
	SSize_t cnt   = PerlIO_get_cnt(f);
	STDCHAR *ptr  = PerlIO_get_ptr(f);
	SSize_t avail = ptr - base;
	if (avail > 0) {
	    if (avail > count) {
		avail = count;
	    }
	    ptr -= avail;
	    Move(buf-avail,ptr,avail,STDCHAR);
	    count -= avail;
	    unread += avail;
	    PerlIO_set_ptrcnt(f,ptr,cnt+avail);
	    if (PerlSIO_feof(s) && unread >= 0)
		PerlSIO_clearerr(s);
	}
    }
    else
#endif
    if (PerlIO_has_cntptr(f)) {
	/* We can get pointer to buffer but not its base
	   Do ungetc() but check chars are ending up in the
	   buffer
	 */
	STDCHAR *eptr = (STDCHAR*)PerlSIO_get_ptr(s);
	STDCHAR *buf = ((STDCHAR *) vbuf) + count;
	while (count > 0) {
	    const int ch = *--buf & 0xFF;
	    if (ungetc(ch,s) != ch) {
		/* ungetc did not work */
		break;
	    }
	    if ((STDCHAR*)PerlSIO_get_ptr(s) != --eptr || ((*eptr & 0xFF) != ch)) {
		/* Did not change pointer as expected */
		fgetc(s);  /* get char back again */
		break;
	    }
	    /* It worked ! */
	    count--;
	    unread++;
	}
    }

    if (count > 0) {
	unread += PerlIOBase_unread(aTHX_ f, vbuf, count);
    }
    return unread;
}

SSize_t
PerlIOStdio_write(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    dVAR;
    SSize_t got;
    for (;;) {
	got = PerlSIO_fwrite(vbuf, 1, count,
			      PerlIOSelf(f, PerlIOStdio)->stdio);
	if (got >= 0 || errno != EINTR)
	    break;
	PERL_ASYNC_CHECK();
	SETERRNO(0,0);	/* just in case */
    }
    return got;
}

IV
PerlIOStdio_seek(pTHX_ PerlIO *f, Off_t offset, int whence)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    PERL_UNUSED_CONTEXT;

    return PerlSIO_fseek(stdio, offset, whence);
}

Off_t
PerlIOStdio_tell(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    PERL_UNUSED_CONTEXT;

    return PerlSIO_ftell(stdio);
}

IV
PerlIOStdio_flush(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    PERL_UNUSED_CONTEXT;

    if (PerlIOBase(f)->flags & PERLIO_F_CANWRITE) {
	return PerlSIO_fflush(stdio);
    }
    else {
	NOOP;
#if 0
	/*
	 * FIXME: This discards ungetc() and pre-read stuff which is not
	 * right if this is just a "sync" from a layer above Suspect right
	 * design is to do _this_ but not have layer above flush this
	 * layer read-to-read
	 */
	/*
	 * Not writeable - sync by attempting a seek
	 */
	const int err = errno;
	if (PerlSIO_fseek(stdio, (Off_t) 0, SEEK_CUR) != 0)
	    errno = err;
#endif
    }
    return 0;
}

IV
PerlIOStdio_eof(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;

    return PerlSIO_feof(PerlIOSelf(f, PerlIOStdio)->stdio);
}

IV
PerlIOStdio_error(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;

    return PerlSIO_ferror(PerlIOSelf(f, PerlIOStdio)->stdio);
}

void
PerlIOStdio_clearerr(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;

    PerlSIO_clearerr(PerlIOSelf(f, PerlIOStdio)->stdio);
}

void
PerlIOStdio_setlinebuf(pTHX_ PerlIO *f)
{
    PERL_UNUSED_CONTEXT;

#ifdef HAS_SETLINEBUF
    PerlSIO_setlinebuf(PerlIOSelf(f, PerlIOStdio)->stdio);
#else
    PerlSIO_setvbuf(PerlIOSelf(f, PerlIOStdio)->stdio, NULL, _IOLBF, 0);
#endif
}

#ifdef FILE_base
STDCHAR *
PerlIOStdio_get_base(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    return (STDCHAR*)PerlSIO_get_base(stdio);
}

Size_t
PerlIOStdio_get_bufsiz(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    return PerlSIO_get_bufsiz(stdio);
}
#endif

#ifdef USE_STDIO_PTR
STDCHAR *
PerlIOStdio_get_ptr(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    return (STDCHAR*)PerlSIO_get_ptr(stdio);
}

SSize_t
PerlIOStdio_get_cnt(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    return PerlSIO_get_cnt(stdio);
}

void
PerlIOStdio_set_ptrcnt(pTHX_ PerlIO *f, STDCHAR * ptr, SSize_t cnt)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    if (ptr != NULL) {
#ifdef STDIO_PTR_LVALUE
	PerlSIO_set_ptr(stdio, ptr); /* LHS STDCHAR* cast non-portable */
#ifdef STDIO_PTR_LVAL_SETS_CNT
	if (PerlSIO_get_cnt(stdio) != (cnt)) {
	    assert(PerlSIO_get_cnt(stdio) == (cnt));
	}
#endif
#if (!defined(STDIO_PTR_LVAL_NOCHANGE_CNT))
	/*
	 * Setting ptr _does_ change cnt - we are done
	 */
	return;
#endif
#else                           /* STDIO_PTR_LVALUE */
	PerlProc_abort();
#endif                          /* STDIO_PTR_LVALUE */
    }
    /*
     * Now (or only) set cnt
     */
#ifdef STDIO_CNT_LVALUE
    PerlSIO_set_cnt(stdio, cnt);
#else                           /* STDIO_CNT_LVALUE */
#if (defined(STDIO_PTR_LVALUE) && defined(STDIO_PTR_LVAL_SETS_CNT))
    PerlSIO_set_ptr(stdio,
		    PerlSIO_get_ptr(stdio) + (PerlSIO_get_cnt(stdio) -
					      cnt));
#else                           /* STDIO_PTR_LVAL_SETS_CNT */
    PerlProc_abort();
#endif                          /* STDIO_PTR_LVAL_SETS_CNT */
#endif                          /* STDIO_CNT_LVALUE */
}


#endif

IV
PerlIOStdio_fill(pTHX_ PerlIO *f)
{
    FILE * const stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    int c;
    PERL_UNUSED_CONTEXT;

    /*
     * fflush()ing read-only streams can cause trouble on some stdio-s
     */
    if ((PerlIOBase(f)->flags & PERLIO_F_CANWRITE)) {
	if (PerlSIO_fflush(stdio) != 0)
	    return EOF;
    }
    for (;;) {
	c = PerlSIO_fgetc(stdio);
	if (c != EOF)
	    break;
	if (! PerlSIO_ferror(stdio) || errno != EINTR)
	    return EOF;
	PERL_ASYNC_CHECK();
	SETERRNO(0,0);
    }

#if (defined(STDIO_PTR_LVALUE) && (defined(STDIO_CNT_LVALUE) || defined(STDIO_PTR_LVAL_SETS_CNT)))

#ifdef STDIO_BUFFER_WRITABLE
    if (PerlIO_fast_gets(f) && PerlIO_has_base(f)) {
	/* Fake ungetc() to the real buffer in case system's ungetc
	   goes elsewhere
	 */
	STDCHAR *base = (STDCHAR*)PerlSIO_get_base(stdio);
	SSize_t cnt   = PerlSIO_get_cnt(stdio);
	STDCHAR *ptr  = (STDCHAR*)PerlSIO_get_ptr(stdio);
	if (ptr == base+1) {
	    *--ptr = (STDCHAR) c;
	    PerlIOStdio_set_ptrcnt(aTHX_ f,ptr,cnt+1);
	    if (PerlSIO_feof(stdio))
		PerlSIO_clearerr(stdio);
	    return 0;
	}
    }
    else
#endif
    if (PerlIO_has_cntptr(f)) {
	STDCHAR ch = c;
	if (PerlIOStdio_unread(aTHX_ f,&ch,1) == 1) {
	    return 0;
	}
    }
#endif

#if defined(VMS)
    /* An ungetc()d char is handled separately from the regular
     * buffer, so we stuff it in the buffer ourselves.
     * Should never get called as should hit code above
     */
    *(--((*stdio)->_ptr)) = (unsigned char) c;
    (*stdio)->_cnt++;
#else
    /* If buffer snoop scheme above fails fall back to
       using ungetc().
     */
    if (PerlSIO_ungetc(c, stdio) != c)
	return EOF;
#endif
    return 0;
}


PERLIO_FUNCS_DECL(PerlIO_stdio) = {
    sizeof(PerlIO_funcs),
    "stdio",
    sizeof(PerlIOStdio),
    PERLIO_K_BUFFERED|PERLIO_K_RAW,
    PerlIOStdio_pushed,
    PerlIOBase_popped,
    PerlIOStdio_open,
    PerlIOBase_binmode,         /* binmode */
    NULL,
    PerlIOStdio_fileno,
    PerlIOStdio_dup,
    PerlIOStdio_read,
    PerlIOStdio_unread,
    PerlIOStdio_write,
    PerlIOStdio_seek,
    PerlIOStdio_tell,
    PerlIOStdio_close,
    PerlIOStdio_flush,
    PerlIOStdio_fill,
    PerlIOStdio_eof,
    PerlIOStdio_error,
    PerlIOStdio_clearerr,
    PerlIOStdio_setlinebuf,
#ifdef FILE_base
    PerlIOStdio_get_base,
    PerlIOStdio_get_bufsiz,
#else
    NULL,
    NULL,
#endif
#ifdef USE_STDIO_PTR
    PerlIOStdio_get_ptr,
    PerlIOStdio_get_cnt,
#   if defined(HAS_FAST_STDIO) && defined(USE_FAST_STDIO)
    PerlIOStdio_set_ptrcnt,
#   else
    NULL,
#   endif /* HAS_FAST_STDIO && USE_FAST_STDIO */
#else
    NULL,
    NULL,
    NULL,
#endif /* USE_STDIO_PTR */
};

/* Note that calls to PerlIO_exportFILE() are reversed using
 * PerlIO_releaseFILE(), not importFILE. */
FILE *
PerlIO_exportFILE(PerlIO * f, const char *mode)
{
    dTHX;
    FILE *stdio = NULL;
    if (PerlIOValid(f)) {
	char buf[8];
	PerlIO_flush(f);
	if (!mode || !*mode) {
	    mode = PerlIO_modestr(f, buf);
	}
	stdio = PerlSIO_fdopen(PerlIO_fileno(f), mode);
	if (stdio) {
	    PerlIOl *l = *f;
	    PerlIO *f2;
	    /* De-link any lower layers so new :stdio sticks */
	    *f = NULL;
	    if ((f2 = PerlIO_push(aTHX_ f, PERLIO_FUNCS_CAST(&PerlIO_stdio), buf, NULL))) {
		PerlIOStdio *s = PerlIOSelf((f = f2), PerlIOStdio);
		s->stdio = stdio;
		PerlIOUnix_refcnt_inc(fileno(stdio));
		/* Link previous lower layers under new one */
		*PerlIONext(f) = l;
	    }
	    else {
		/* restore layers list */
		*f = l;
	    }
	}
    }
    return stdio;
}


FILE *
PerlIO_findFILE(PerlIO *f)
{
    PerlIOl *l = *f;
    FILE *stdio;
    while (l) {
	if (l->tab == &PerlIO_stdio) {
	    PerlIOStdio *s = PerlIOSelf(&l, PerlIOStdio);
	    return s->stdio;
	}
	l = *PerlIONext(&l);
    }
    /* Uses fallback "mode" via PerlIO_modestr() in PerlIO_exportFILE */
    /* However, we're not really exporting a FILE * to someone else (who
       becomes responsible for closing it, or calling PerlIO_releaseFILE())
       So we need to undo its refernce count increase on the underlying file
       descriptor. We have to do this, because if the loop above returns you
       the FILE *, then *it* didn't increase any reference count. So there's
       only one way to be consistent. */
    stdio = PerlIO_exportFILE(f, NULL);
    if (stdio) {
	const int fd = fileno(stdio);
	if (fd >= 0)
	    PerlIOUnix_refcnt_dec(fd);
    }
    return stdio;
}

/* Use this to reverse PerlIO_exportFILE calls. */
void
PerlIO_releaseFILE(PerlIO *p, FILE *f)
{
    dVAR;
    PerlIOl *l;
    while ((l = *p)) {
	if (l->tab == &PerlIO_stdio) {
	    PerlIOStdio *s = PerlIOSelf(&l, PerlIOStdio);
	    if (s->stdio == f) {
		dTHX;
		const int fd = fileno(f);
		if (fd >= 0)
		    PerlIOUnix_refcnt_dec(fd);
		PerlIO_pop(aTHX_ p);
		return;
	    }
	}
	p = PerlIONext(p);
    }
    return;
}

/*--------------------------------------------------------------------------------------*/
/*
 * perlio buffer layer
 */

IV
PerlIOBuf_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    PerlIOBuf *b = PerlIOSelf(f, PerlIOBuf);
    const int fd = PerlIO_fileno(f);
    if (fd >= 0 && PerlLIO_isatty(fd)) {
	PerlIOBase(f)->flags |= PERLIO_F_LINEBUF | PERLIO_F_TTY;
    }
    if (*PerlIONext(f)) {
	const Off_t posn = PerlIO_tell(PerlIONext(f));
	if (posn != (Off_t) - 1) {
	    b->posn = posn;
	}
    }
    return PerlIOBase_pushed(aTHX_ f, mode, arg, tab);
}

PerlIO *
PerlIOBuf_open(pTHX_ PerlIO_funcs *self, PerlIO_list_t *layers,
	       IV n, const char *mode, int fd, int imode, int perm,
	       PerlIO *f, int narg, SV **args)
{
    if (PerlIOValid(f)) {
	PerlIO *next = PerlIONext(f);
	PerlIO_funcs *tab =
	     PerlIO_layer_fetch(aTHX_ layers, n - 1, PerlIOBase(next)->tab);
	if (tab && tab->Open)
	     next =
		  (*tab->Open)(aTHX_ tab, layers, n - 1, mode, fd, imode, perm,
			       next, narg, args);
	if (!next || (*PerlIOBase(f)->tab->Pushed) (aTHX_ f, mode, PerlIOArg, self) != 0) {
	    return NULL;
	}
    }
    else {
	PerlIO_funcs *tab = PerlIO_layer_fetch(aTHX_ layers, n - 1, PerlIO_default_btm());
	int init = 0;
	if (*mode == IoTYPE_IMPLICIT) {
	    init = 1;
	    /*
	     * mode++;
	     */
	}
	if (tab && tab->Open)
	     f = (*tab->Open)(aTHX_ tab, layers, n - 1, mode, fd, imode, perm,
			      f, narg, args);
	else
	     SETERRNO(EINVAL, LIB_INVARG);
	if (f) {
	    if (PerlIO_push(aTHX_ f, self, mode, PerlIOArg) == 0) {
		/*
		 * if push fails during open, open fails. close will pop us.
		 */
		PerlIO_close (f);
		return NULL;
	    } else {
		fd = PerlIO_fileno(f);
		if (init && fd == 2) {
		    /*
		     * Initial stderr is unbuffered
		     */
		    PerlIOBase(f)->flags |= PERLIO_F_UNBUF;
		}
#ifdef PERLIO_USING_CRLF
#  ifdef PERLIO_IS_BINMODE_FD
		if (PERLIO_IS_BINMODE_FD(fd))
		    PerlIO_binmode(aTHX_ f,  '<'/*not used*/, O_BINARY, NULL);
		else
#  endif
		/*
		 * do something about failing setmode()? --jhi
		 */
		PerlLIO_setmode(fd, O_BINARY);
#endif
	    }
	}
    }
    return f;
}

/*
 * This "flush" is akin to sfio's sync in that it handles files in either
 * read or write state.  For write state, we put the postponed data through
 * the next layers.  For read state, we seek() the next layers to the
 * offset given by current position in the buffer, and discard the buffer
 * state (XXXX supposed to be for seek()able buffers only, but now it is done
 * in any case?).  Then the pass the stick further in chain.
 */
IV
PerlIOBuf_flush(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    int code = 0;
    PerlIO *n = PerlIONext(f);
    if (PerlIOBase(f)->flags & PERLIO_F_WRBUF) {
	/*
	 * write() the buffer
	 */
	const STDCHAR *buf = b->buf;
	const STDCHAR *p = buf;
	while (p < b->ptr) {
	    SSize_t count = PerlIO_write(n, p, b->ptr - p);
	    if (count > 0) {
		p += count;
	    }
	    else if (count < 0 || PerlIO_error(n)) {
		PerlIOBase(f)->flags |= PERLIO_F_ERROR;
		code = -1;
		break;
	    }
	}
	b->posn += (p - buf);
    }
    else if (PerlIOBase(f)->flags & PERLIO_F_RDBUF) {
	STDCHAR *buf = PerlIO_get_base(f);
	/*
	 * Note position change
	 */
	b->posn += (b->ptr - buf);
	if (b->ptr < b->end) {
	    /* We did not consume all of it - try and seek downstream to
	       our logical position
	     */
	    if (PerlIOValid(n) && PerlIO_seek(n, b->posn, SEEK_SET) == 0) {
		/* Reload n as some layers may pop themselves on seek */
		b->posn = PerlIO_tell(n = PerlIONext(f));
	    }
	    else {
		/* Seek failed (e.g. pipe or tty). Do NOT clear buffer or pre-read
		   data is lost for good - so return saying "ok" having undone
		   the position adjust
		 */
		b->posn -= (b->ptr - buf);
		return code;
	    }
	}
    }
    b->ptr = b->end = b->buf;
    PerlIOBase(f)->flags &= ~(PERLIO_F_RDBUF | PERLIO_F_WRBUF);
    /* We check for Valid because of dubious decision to make PerlIO_flush(NULL) flush all */
    if (PerlIOValid(n) && PerlIO_flush(n) != 0)
	code = -1;
    return code;
}

/* This discards the content of the buffer after b->ptr, and rereads
 * the buffer from the position off in the layer downstream; here off
 * is at offset corresponding to b->ptr - b->buf.
 */
IV
PerlIOBuf_fill(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    PerlIO *n = PerlIONext(f);
    SSize_t avail;
    /*
     * Down-stream flush is defined not to loose read data so is harmless.
     * we would not normally be fill'ing if there was data left in anycase.
     */
    if (PerlIO_flush(f) != 0)	/* XXXX Check that its seek() succeeded?! */
	return -1;
    if (PerlIOBase(f)->flags & PERLIO_F_TTY)
	PerlIOBase_flush_linebuf(aTHX);

    if (!b->buf)
	PerlIO_get_base(f);     /* allocate via vtable */

    assert(b->buf); /* The b->buf does get allocated via the vtable system. */

    b->ptr = b->end = b->buf;

    if (!PerlIOValid(n)) {
	PerlIOBase(f)->flags |= PERLIO_F_EOF;
	return -1;
    }

    if (PerlIO_fast_gets(n)) {
	/*
	 * Layer below is also buffered. We do _NOT_ want to call its
	 * ->Read() because that will loop till it gets what we asked for
	 * which may hang on a pipe etc. Instead take anything it has to
	 * hand, or ask it to fill _once_.
	 */
	avail = PerlIO_get_cnt(n);
	if (avail <= 0) {
	    avail = PerlIO_fill(n);
	    if (avail == 0)
		avail = PerlIO_get_cnt(n);
	    else {
		if (!PerlIO_error(n) && PerlIO_eof(n))
		    avail = 0;
	    }
	}
	if (avail > 0) {
	    STDCHAR *ptr = PerlIO_get_ptr(n);
	    const SSize_t cnt = avail;
	    if (avail > (SSize_t)b->bufsiz)
		avail = b->bufsiz;
	    Copy(ptr, b->buf, avail, STDCHAR);
	    PerlIO_set_ptrcnt(n, ptr + avail, cnt - avail);
	}
    }
    else {
	avail = PerlIO_read(n, b->ptr, b->bufsiz);
    }
    if (avail <= 0) {
	if (avail == 0)
	    PerlIOBase(f)->flags |= PERLIO_F_EOF;
	else
	    PerlIOBase(f)->flags |= PERLIO_F_ERROR;
	return -1;
    }
    b->end = b->buf + avail;
    PerlIOBase(f)->flags |= PERLIO_F_RDBUF;
    return 0;
}

SSize_t
PerlIOBuf_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
{
    if (PerlIOValid(f)) {
        const PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
	if (!b->ptr)
	    PerlIO_get_base(f);
	return PerlIOBase_read(aTHX_ f, vbuf, count);
    }
    return 0;
}

SSize_t
PerlIOBuf_unread(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    const STDCHAR *buf = (const STDCHAR *) vbuf + count;
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    SSize_t unread = 0;
    SSize_t avail;
    if (PerlIOBase(f)->flags & PERLIO_F_WRBUF)
	PerlIO_flush(f);
    if (!b->buf)
	PerlIO_get_base(f);
    if (b->buf) {
	if (PerlIOBase(f)->flags & PERLIO_F_RDBUF) {
	    /*
	     * Buffer is already a read buffer, we can overwrite any chars
	     * which have been read back to buffer start
	     */
	    avail = (b->ptr - b->buf);
	}
	else {
	    /*
	     * Buffer is idle, set it up so whole buffer is available for
	     * unread
	     */
	    avail = b->bufsiz;
	    b->end = b->buf + avail;
	    b->ptr = b->end;
	    PerlIOBase(f)->flags |= PERLIO_F_RDBUF;
	    /*
	     * Buffer extends _back_ from where we are now
	     */
	    b->posn -= b->bufsiz;
	}
	if (avail > (SSize_t) count) {
	    /*
	     * If we have space for more than count, just move count
	     */
	    avail = count;
	}
	if (avail > 0) {
	    b->ptr -= avail;
	    buf -= avail;
	    /*
	     * In simple stdio-like ungetc() case chars will be already
	     * there
	     */
	    if (buf != b->ptr) {
		Copy(buf, b->ptr, avail, STDCHAR);
	    }
	    count -= avail;
	    unread += avail;
	    PerlIOBase(f)->flags &= ~PERLIO_F_EOF;
	}
    }
    if (count > 0) {
	unread += PerlIOBase_unread(aTHX_ f, vbuf, count);
    }
    return unread;
}

SSize_t
PerlIOBuf_write(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    const STDCHAR *buf = (const STDCHAR *) vbuf;
    const STDCHAR *flushptr = buf;
    Size_t written = 0;
    if (!b->buf)
	PerlIO_get_base(f);
    if (!(PerlIOBase(f)->flags & PERLIO_F_CANWRITE))
	return 0;
    if (PerlIOBase(f)->flags & PERLIO_F_RDBUF) {
    	if (PerlIO_flush(f) != 0) {
	    return 0;
	}
    }	
    if (PerlIOBase(f)->flags & PERLIO_F_LINEBUF) {
	flushptr = buf + count;
	while (flushptr > buf && *(flushptr - 1) != '\n')
	    --flushptr;
    }
    while (count > 0) {
	SSize_t avail = b->bufsiz - (b->ptr - b->buf);
	if ((SSize_t) count < avail)
	    avail = count;
	if (flushptr > buf && flushptr <= buf + avail)
	    avail = flushptr - buf;
	PerlIOBase(f)->flags |= PERLIO_F_WRBUF;
	if (avail) {
	    Copy(buf, b->ptr, avail, STDCHAR);
	    count -= avail;
	    buf += avail;
	    written += avail;
	    b->ptr += avail;
	    if (buf == flushptr)
		PerlIO_flush(f);
	}
	if (b->ptr >= (b->buf + b->bufsiz))
	    PerlIO_flush(f);
    }
    if (PerlIOBase(f)->flags & PERLIO_F_UNBUF)
	PerlIO_flush(f);
    return written;
}

IV
PerlIOBuf_seek(pTHX_ PerlIO *f, Off_t offset, int whence)
{
    IV code;
    if ((code = PerlIO_flush(f)) == 0) {
	PerlIOBase(f)->flags &= ~PERLIO_F_EOF;
	code = PerlIO_seek(PerlIONext(f), offset, whence);
	if (code == 0) {
	    PerlIOBuf *b = PerlIOSelf(f, PerlIOBuf);
	    b->posn = PerlIO_tell(PerlIONext(f));
	}
    }
    return code;
}

Off_t
PerlIOBuf_tell(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    /*
     * b->posn is file position where b->buf was read, or will be written
     */
    Off_t posn = b->posn;
    if ((PerlIOBase(f)->flags & PERLIO_F_APPEND) &&
        (PerlIOBase(f)->flags & PERLIO_F_WRBUF)) {
#if 1
    	/* As O_APPEND files are normally shared in some sense it is better
	   to flush :
	 */  	
	PerlIO_flush(f);
#else	
        /* when file is NOT shared then this is sufficient */
	PerlIO_seek(PerlIONext(f),0, SEEK_END);
#endif
	posn = b->posn = PerlIO_tell(PerlIONext(f));
    }
    if (b->buf) {
	/*
	 * If buffer is valid adjust position by amount in buffer
	 */
	posn += (b->ptr - b->buf);
    }
    return posn;
}

IV
PerlIOBuf_popped(pTHX_ PerlIO *f)
{
    const IV code = PerlIOBase_popped(aTHX_ f);
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (b->buf && b->buf != (STDCHAR *) & b->oneword) {
	Safefree(b->buf);
    }
    b->ptr = b->end = b->buf = NULL;
    PerlIOBase(f)->flags &= ~(PERLIO_F_RDBUF | PERLIO_F_WRBUF);
    return code;
}

IV
PerlIOBuf_close(pTHX_ PerlIO *f)
{
    const IV code = PerlIOBase_close(aTHX_ f);
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (b->buf && b->buf != (STDCHAR *) & b->oneword) {
	Safefree(b->buf);
    }
    b->ptr = b->end = b->buf = NULL;
    PerlIOBase(f)->flags &= ~(PERLIO_F_RDBUF | PERLIO_F_WRBUF);
    return code;
}

STDCHAR *
PerlIOBuf_get_ptr(pTHX_ PerlIO *f)
{
    const PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (!b->buf)
	PerlIO_get_base(f);
    return b->ptr;
}

SSize_t
PerlIOBuf_get_cnt(pTHX_ PerlIO *f)
{
    const PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (!b->buf)
	PerlIO_get_base(f);
    if (PerlIOBase(f)->flags & PERLIO_F_RDBUF)
	return (b->end - b->ptr);
    return 0;
}

STDCHAR *
PerlIOBuf_get_base(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    PERL_UNUSED_CONTEXT;

    if (!b->buf) {
	if (!b->bufsiz)
	    b->bufsiz = 4096;
	b->buf = Newxz(b->buf,b->bufsiz, STDCHAR);
	if (!b->buf) {
	    b->buf = (STDCHAR *) & b->oneword;
	    b->bufsiz = sizeof(b->oneword);
	}
	b->end = b->ptr = b->buf;
    }
    return b->buf;
}

Size_t
PerlIOBuf_bufsiz(pTHX_ PerlIO *f)
{
    const PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (!b->buf)
	PerlIO_get_base(f);
    return (b->end - b->buf);
}

void
PerlIOBuf_set_ptrcnt(pTHX_ PerlIO *f, STDCHAR * ptr, SSize_t cnt)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (!b->buf)
	PerlIO_get_base(f);
    b->ptr = ptr;
    if (PerlIO_get_cnt(f) != cnt || b->ptr < b->buf) {
	assert(PerlIO_get_cnt(f) == cnt);
	assert(b->ptr >= b->buf);
    }
    PerlIOBase(f)->flags |= PERLIO_F_RDBUF;
}

PerlIO *
PerlIOBuf_dup(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags)
{
 return PerlIOBase_dup(aTHX_ f, o, param, flags);
}


PERLIO_FUNCS_DECL(PerlIO_perlio) = {
    sizeof(PerlIO_funcs),
    "perlio",
    sizeof(PerlIOBuf),
    PERLIO_K_BUFFERED|PERLIO_K_RAW,
    PerlIOBuf_pushed,
    PerlIOBuf_popped,
    PerlIOBuf_open,
    PerlIOBase_binmode,         /* binmode */
    NULL,
    PerlIOBase_fileno,
    PerlIOBuf_dup,
    PerlIOBuf_read,
    PerlIOBuf_unread,
    PerlIOBuf_write,
    PerlIOBuf_seek,
    PerlIOBuf_tell,
    PerlIOBuf_close,
    PerlIOBuf_flush,
    PerlIOBuf_fill,
    PerlIOBase_eof,
    PerlIOBase_error,
    PerlIOBase_clearerr,
    PerlIOBase_setlinebuf,
    PerlIOBuf_get_base,
    PerlIOBuf_bufsiz,
    PerlIOBuf_get_ptr,
    PerlIOBuf_get_cnt,
    PerlIOBuf_set_ptrcnt,
};

/*--------------------------------------------------------------------------------------*/
/*
 * Temp layer to hold unread chars when cannot do it any other way
 */

IV
PerlIOPending_fill(pTHX_ PerlIO *f)
{
    /*
     * Should never happen
     */
    PerlIO_flush(f);
    return 0;
}

IV
PerlIOPending_close(pTHX_ PerlIO *f)
{
    /*
     * A tad tricky - flush pops us, then we close new top
     */
    PerlIO_flush(f);
    return PerlIO_close(f);
}

IV
PerlIOPending_seek(pTHX_ PerlIO *f, Off_t offset, int whence)
{
    /*
     * A tad tricky - flush pops us, then we seek new top
     */
    PerlIO_flush(f);
    return PerlIO_seek(f, offset, whence);
}


IV
PerlIOPending_flush(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (b->buf && b->buf != (STDCHAR *) & b->oneword) {
	Safefree(b->buf);
	b->buf = NULL;
    }
    PerlIO_pop(aTHX_ f);
    return 0;
}

void
PerlIOPending_set_ptrcnt(pTHX_ PerlIO *f, STDCHAR * ptr, SSize_t cnt)
{
    if (cnt <= 0) {
	PerlIO_flush(f);
    }
    else {
	PerlIOBuf_set_ptrcnt(aTHX_ f, ptr, cnt);
    }
}

IV
PerlIOPending_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    const IV code = PerlIOBase_pushed(aTHX_ f, mode, arg, tab);
    PerlIOl * const l = PerlIOBase(f);
    /*
     * Our PerlIO_fast_gets must match what we are pushed on, or sv_gets()
     * etc. get muddled when it changes mid-string when we auto-pop.
     */
    l->flags = (l->flags & ~(PERLIO_F_FASTGETS | PERLIO_F_UTF8)) |
	(PerlIOBase(PerlIONext(f))->
	 flags & (PERLIO_F_FASTGETS | PERLIO_F_UTF8));
    return code;
}

SSize_t
PerlIOPending_read(pTHX_ PerlIO *f, void *vbuf, Size_t count)
{
    SSize_t avail = PerlIO_get_cnt(f);
    SSize_t got = 0;
    if ((SSize_t)count < avail)
	avail = count;
    if (avail > 0)
	got = PerlIOBuf_read(aTHX_ f, vbuf, avail);
    if (got >= 0 && got < (SSize_t)count) {
	const SSize_t more =
	    PerlIO_read(f, ((STDCHAR *) vbuf) + got, count - got);
	if (more >= 0 || got == 0)
	    got += more;
    }
    return got;
}

PERLIO_FUNCS_DECL(PerlIO_pending) = {
    sizeof(PerlIO_funcs),
    "pending",
    sizeof(PerlIOBuf),
    PERLIO_K_BUFFERED|PERLIO_K_RAW,  /* not sure about RAW here */
    PerlIOPending_pushed,
    PerlIOBuf_popped,
    NULL,
    PerlIOBase_binmode,         /* binmode */
    NULL,
    PerlIOBase_fileno,
    PerlIOBuf_dup,
    PerlIOPending_read,
    PerlIOBuf_unread,
    PerlIOBuf_write,
    PerlIOPending_seek,
    PerlIOBuf_tell,
    PerlIOPending_close,
    PerlIOPending_flush,
    PerlIOPending_fill,
    PerlIOBase_eof,
    PerlIOBase_error,
    PerlIOBase_clearerr,
    PerlIOBase_setlinebuf,
    PerlIOBuf_get_base,
    PerlIOBuf_bufsiz,
    PerlIOBuf_get_ptr,
    PerlIOBuf_get_cnt,
    PerlIOPending_set_ptrcnt,
};


/*--------------------------------------------------------------------------------------*/
/*
 * crlf - translation On read translate CR,LF to "\n" we do this by
 * overriding ptr/cnt entries to hand back a line at a time and keeping a
 * record of which nl we "lied" about. On write translate "\n" to CR,LF
 *
 * c->nl points on the first byte of CR LF pair when it is temporarily
 * replaced by LF, or to the last CR of the buffer.  In the former case
 * the caller thinks that the buffer ends at c->nl + 1, in the latter
 * that it ends at c->nl; these two cases can be distinguished by
 * *c->nl.  c->nl is set during _getcnt() call, and unset during
 * _unread() and _flush() calls.
 * It only matters for read operations.
 */

typedef struct {
    PerlIOBuf base;             /* PerlIOBuf stuff */
    STDCHAR *nl;                /* Position of crlf we "lied" about in the
				 * buffer */
} PerlIOCrlf;

/* Inherit the PERLIO_F_UTF8 flag from previous layer.
 * Otherwise the :crlf layer would always revert back to
 * raw mode.
 */
static void
S_inherit_utf8_flag(PerlIO *f)
{
    PerlIO *g = PerlIONext(f);
    if (PerlIOValid(g)) {
	if (PerlIOBase(g)->flags & PERLIO_F_UTF8) {
	    PerlIOBase(f)->flags |= PERLIO_F_UTF8;
	}
    }
}

IV
PerlIOCrlf_pushed(pTHX_ PerlIO *f, const char *mode, SV *arg, PerlIO_funcs *tab)
{
    IV code;
    PerlIOBase(f)->flags |= PERLIO_F_CRLF;
    code = PerlIOBuf_pushed(aTHX_ f, mode, arg, tab);
#if 0
    PerlIO_debug("PerlIOCrlf_pushed f=%p %s %s fl=%08" UVxf "\n",
		 (void*)f, PerlIOBase(f)->tab->name, (mode) ? mode : "(Null)",
		 PerlIOBase(f)->flags);
#endif
    {
      /* Enable the first CRLF capable layer you can find, but if none
       * found, the one we just pushed is fine.  This results in at
       * any given moment at most one CRLF-capable layer being enabled
       * in the whole layer stack. */
	 PerlIO *g = PerlIONext(f);
	 while (PerlIOValid(g)) {
	      PerlIOl *b = PerlIOBase(g);
	      if (b && b->tab == &PerlIO_crlf) {
		   if (!(b->flags & PERLIO_F_CRLF))
			b->flags |= PERLIO_F_CRLF;
		   S_inherit_utf8_flag(g);
		   PerlIO_pop(aTHX_ f);
		   return code;
	      }		  
	      g = PerlIONext(g);
	 }
    }
    S_inherit_utf8_flag(f);
    return code;
}


SSize_t
PerlIOCrlf_unread(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    PerlIOCrlf * const c = PerlIOSelf(f, PerlIOCrlf);
    if (c->nl) {	/* XXXX Shouldn't it be done only if b->ptr > c->nl? */
	*(c->nl) = 0xd;
	c->nl = NULL;
    }
    if (!(PerlIOBase(f)->flags & PERLIO_F_CRLF))
	return PerlIOBuf_unread(aTHX_ f, vbuf, count);
    else {
	const STDCHAR *buf = (const STDCHAR *) vbuf + count;
	PerlIOBuf *b = PerlIOSelf(f, PerlIOBuf);
	SSize_t unread = 0;
	if (PerlIOBase(f)->flags & PERLIO_F_WRBUF)
	    PerlIO_flush(f);
	if (!b->buf)
	    PerlIO_get_base(f);
	if (b->buf) {
	    if (!(PerlIOBase(f)->flags & PERLIO_F_RDBUF)) {
		b->end = b->ptr = b->buf + b->bufsiz;
		PerlIOBase(f)->flags |= PERLIO_F_RDBUF;
		b->posn -= b->bufsiz;
	    }
	    while (count > 0 && b->ptr > b->buf) {
		const int ch = *--buf;
		if (ch == '\n') {
		    if (b->ptr - 2 >= b->buf) {
			*--(b->ptr) = 0xa;
			*--(b->ptr) = 0xd;
			unread++;
			count--;
		    }
		    else {
		    /* If b->ptr - 1 == b->buf, we are undoing reading 0xa */
			*--(b->ptr) = 0xa;	/* Works even if 0xa == '\r' */
			unread++;
			count--;
		    }
		}
		else {
		    *--(b->ptr) = ch;
		    unread++;
		    count--;
		}
	    }
	}
	return unread;
    }
}

/* XXXX This code assumes that buffer size >=2, but does not check it... */
SSize_t
PerlIOCrlf_get_cnt(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    if (!b->buf)
	PerlIO_get_base(f);
    if (PerlIOBase(f)->flags & PERLIO_F_RDBUF) {
	PerlIOCrlf * const c = PerlIOSelf(f, PerlIOCrlf);
	if ((PerlIOBase(f)->flags & PERLIO_F_CRLF) && (!c->nl || *c->nl == 0xd)) {
	    STDCHAR *nl = (c->nl) ? c->nl : b->ptr;
	  scan:
	    while (nl < b->end && *nl != 0xd)
		nl++;
	    if (nl < b->end && *nl == 0xd) {
	      test:
		if (nl + 1 < b->end) {
		    if (nl[1] == 0xa) {
			*nl = '\n';
			c->nl = nl;
		    }
		    else {
			/*
			 * Not CR,LF but just CR
			 */
			nl++;
			goto scan;
		    }
		}
		else {
		    /*
		     * Blast - found CR as last char in buffer
		     */

		    if (b->ptr < nl) {
			/*
			 * They may not care, defer work as long as
			 * possible
			 */
			c->nl = nl;
			return (nl - b->ptr);
		    }
		    else {
			int code;
			b->ptr++;       /* say we have read it as far as
					 * flush() is concerned */
			b->buf++;       /* Leave space in front of buffer */
			/* Note as we have moved buf up flush's
			   posn += ptr-buf
			   will naturally make posn point at CR
			 */
			b->bufsiz--;    /* Buffer is thus smaller */
			code = PerlIO_fill(f);  /* Fetch some more */
			b->bufsiz++;    /* Restore size for next time */
			b->buf--;       /* Point at space */
			b->ptr = nl = b->buf;   /* Which is what we hand
						 * off */
			*nl = 0xd;      /* Fill in the CR */
			if (code == 0)
			    goto test;  /* fill() call worked */
			/*
			 * CR at EOF - just fall through
			 */
			/* Should we clear EOF though ??? */
		    }
		}
	    }
	}
	return (((c->nl) ? (c->nl + 1) : b->end) - b->ptr);
    }
    return 0;
}

void
PerlIOCrlf_set_ptrcnt(pTHX_ PerlIO *f, STDCHAR * ptr, SSize_t cnt)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    PerlIOCrlf * const c = PerlIOSelf(f, PerlIOCrlf);
    if (!b->buf)
	PerlIO_get_base(f);
    if (!ptr) {
	if (c->nl) {
	    ptr = c->nl + 1;
	    if (ptr == b->end && *c->nl == 0xd) {
		/* Defered CR at end of buffer case - we lied about count */
		ptr--;
	    }
	}
	else {
	    ptr = b->end;
	}
	ptr -= cnt;
    }
    else {
	NOOP;
#if 0
	/*
	 * Test code - delete when it works ...
	 */
	IV flags = PerlIOBase(f)->flags;
	STDCHAR *chk = (c->nl) ? (c->nl+1) : b->end;
	if (ptr+cnt == c->nl && c->nl+1 == b->end && *c->nl == 0xd) {
	  /* Defered CR at end of buffer case - we lied about count */
	  chk--;
	}
	chk -= cnt;

	if (ptr != chk ) {
	    Perl_croak(aTHX_ "ptr wrong %p != %p fl=%08" UVxf
		       " nl=%p e=%p for %d", (void*)ptr, (void*)chk,
		       flags, c->nl, b->end, cnt);
	}
#endif
    }
    if (c->nl) {
	if (ptr > c->nl) {
	    /*
	     * They have taken what we lied about
	     */
	    *(c->nl) = 0xd;
	    c->nl = NULL;
	    ptr++;
	}
    }
    b->ptr = ptr;
    PerlIOBase(f)->flags |= PERLIO_F_RDBUF;
}

SSize_t
PerlIOCrlf_write(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    if (!(PerlIOBase(f)->flags & PERLIO_F_CRLF))
	return PerlIOBuf_write(aTHX_ f, vbuf, count);
    else {
	PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
	const STDCHAR *buf = (const STDCHAR *) vbuf;
	const STDCHAR * const ebuf = buf + count;
	if (!b->buf)
	    PerlIO_get_base(f);
	if (!(PerlIOBase(f)->flags & PERLIO_F_CANWRITE))
	    return 0;
	while (buf < ebuf) {
	    const STDCHAR * const eptr = b->buf + b->bufsiz;
	    PerlIOBase(f)->flags |= PERLIO_F_WRBUF;
	    while (buf < ebuf && b->ptr < eptr) {
		if (*buf == '\n') {
		    if ((b->ptr + 2) > eptr) {
			/*
			 * Not room for both
			 */
			PerlIO_flush(f);
			break;
		    }
		    else {
			*(b->ptr)++ = 0xd;      /* CR */
			*(b->ptr)++ = 0xa;      /* LF */
			buf++;
			if (PerlIOBase(f)->flags & PERLIO_F_LINEBUF) {
			    PerlIO_flush(f);
			    break;
			}
		    }
		}
		else {
		    *(b->ptr)++ = *buf++;
		}
		if (b->ptr >= eptr) {
		    PerlIO_flush(f);
		    break;
		}
	    }
	}
	if (PerlIOBase(f)->flags & PERLIO_F_UNBUF)
	    PerlIO_flush(f);
	return (buf - (STDCHAR *) vbuf);
    }
}

IV
PerlIOCrlf_flush(pTHX_ PerlIO *f)
{
    PerlIOCrlf * const c = PerlIOSelf(f, PerlIOCrlf);
    if (c->nl) {
	*(c->nl) = 0xd;
	c->nl = NULL;
    }
    return PerlIOBuf_flush(aTHX_ f);
}

IV
PerlIOCrlf_binmode(pTHX_ PerlIO *f)
{
    if ((PerlIOBase(f)->flags & PERLIO_F_CRLF)) {
	/* In text mode - flush any pending stuff and flip it */
	PerlIOBase(f)->flags &= ~PERLIO_F_CRLF;
#ifndef PERLIO_USING_CRLF
	/* CRLF is unusual case - if this is just the :crlf layer pop it */
	if (PerlIOBase(f)->tab == &PerlIO_crlf) {
		PerlIO_pop(aTHX_ f);
	}
#endif
    }
    return 0;
}

PERLIO_FUNCS_DECL(PerlIO_crlf) = {
    sizeof(PerlIO_funcs),
    "crlf",
    sizeof(PerlIOCrlf),
    PERLIO_K_BUFFERED | PERLIO_K_CANCRLF | PERLIO_K_RAW,
    PerlIOCrlf_pushed,
    PerlIOBuf_popped,         /* popped */
    PerlIOBuf_open,
    PerlIOCrlf_binmode,       /* binmode */
    NULL,
    PerlIOBase_fileno,
    PerlIOBuf_dup,
    PerlIOBuf_read,             /* generic read works with ptr/cnt lies */
    PerlIOCrlf_unread,          /* Put CR,LF in buffer for each '\n' */
    PerlIOCrlf_write,           /* Put CR,LF in buffer for each '\n' */
    PerlIOBuf_seek,
    PerlIOBuf_tell,
    PerlIOBuf_close,
    PerlIOCrlf_flush,
    PerlIOBuf_fill,
    PerlIOBase_eof,
    PerlIOBase_error,
    PerlIOBase_clearerr,
    PerlIOBase_setlinebuf,
    PerlIOBuf_get_base,
    PerlIOBuf_bufsiz,
    PerlIOBuf_get_ptr,
    PerlIOCrlf_get_cnt,
    PerlIOCrlf_set_ptrcnt,
};

#ifdef HAS_MMAP
/*--------------------------------------------------------------------------------------*/
/*
 * mmap as "buffer" layer
 */

typedef struct {
    PerlIOBuf base;             /* PerlIOBuf stuff */
    Mmap_t mptr;                /* Mapped address */
    Size_t len;                 /* mapped length */
    STDCHAR *bbuf;              /* malloced buffer if map fails */
} PerlIOMmap;

IV
PerlIOMmap_map(pTHX_ PerlIO *f)
{
    dVAR;
    PerlIOMmap * const m = PerlIOSelf(f, PerlIOMmap);
    const IV flags = PerlIOBase(f)->flags;
    IV code = 0;
    if (m->len)
	abort();
    if (flags & PERLIO_F_CANREAD) {
	PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
	const int fd = PerlIO_fileno(f);
	Stat_t st;
	code = Fstat(fd, &st);
	if (code == 0 && S_ISREG(st.st_mode)) {
	    SSize_t len = st.st_size - b->posn;
	    if (len > 0) {
		Off_t posn;
		if (PL_mmap_page_size <= 0)
		  Perl_croak(aTHX_ "panic: bad pagesize %" IVdf,
			     PL_mmap_page_size);
		if (b->posn < 0) {
		    /*
		     * This is a hack - should never happen - open should
		     * have set it !
		     */
		    b->posn = PerlIO_tell(PerlIONext(f));
		}
		posn = (b->posn / PL_mmap_page_size) * PL_mmap_page_size;
		len = st.st_size - posn;
		m->mptr = (Mmap_t)mmap(NULL, len, PROT_READ, MAP_SHARED, fd, posn);
		if (m->mptr && m->mptr != (Mmap_t) - 1) {
#if 0 && defined(HAS_MADVISE) && defined(MADV_SEQUENTIAL)
		    madvise(m->mptr, len, MADV_SEQUENTIAL);
#endif
#if 0 && defined(HAS_MADVISE) && defined(MADV_WILLNEED)
		    madvise(m->mptr, len, MADV_WILLNEED);
#endif
		    PerlIOBase(f)->flags =
			(flags & ~PERLIO_F_EOF) | PERLIO_F_RDBUF;
		    b->end = ((STDCHAR *) m->mptr) + len;
		    b->buf = ((STDCHAR *) m->mptr) + (b->posn - posn);
		    b->ptr = b->buf;
		    m->len = len;
		}
		else {
		    b->buf = NULL;
		}
	    }
	    else {
		PerlIOBase(f)->flags =
		    flags | PERLIO_F_EOF | PERLIO_F_RDBUF;
		b->buf = NULL;
		b->ptr = b->end = b->ptr;
		code = -1;
	    }
	}
    }
    return code;
}

IV
PerlIOMmap_unmap(pTHX_ PerlIO *f)
{
    PerlIOMmap * const m = PerlIOSelf(f, PerlIOMmap);
    IV code = 0;
    if (m->len) {
	PerlIOBuf * const b = &m->base;
	if (b->buf) {
	    /* The munmap address argument is tricky: depending on the
	     * standard it is either "void *" or "caddr_t" (which is
	     * usually "char *" (signed or unsigned).  If we cast it
	     * to "void *", those that have it caddr_t and an uptight
	     * C++ compiler, will freak out.  But casting it as char*
	     * should work.  Maybe.  (Using Mmap_t figured out by
	     * Configure doesn't always work, apparently.) */
	    code = munmap((char*)m->mptr, m->len);
	    b->buf = NULL;
	    m->len = 0;
	    m->mptr = NULL;
	    if (PerlIO_seek(PerlIONext(f), b->posn, SEEK_SET) != 0)
		code = -1;
	}
	b->ptr = b->end = b->buf;
	PerlIOBase(f)->flags &= ~(PERLIO_F_RDBUF | PERLIO_F_WRBUF);
    }
    return code;
}

STDCHAR *
PerlIOMmap_get_base(pTHX_ PerlIO *f)
{
    PerlIOMmap * const m = PerlIOSelf(f, PerlIOMmap);
    PerlIOBuf * const b = &m->base;
    if (b->buf && (PerlIOBase(f)->flags & PERLIO_F_RDBUF)) {
	/*
	 * Already have a readbuffer in progress
	 */
	return b->buf;
    }
    if (b->buf) {
	/*
	 * We have a write buffer or flushed PerlIOBuf read buffer
	 */
	m->bbuf = b->buf;       /* save it in case we need it again */
	b->buf = NULL;          /* Clear to trigger below */
    }
    if (!b->buf) {
	PerlIOMmap_map(aTHX_ f);        /* Try and map it */
	if (!b->buf) {
	    /*
	     * Map did not work - recover PerlIOBuf buffer if we have one
	     */
	    b->buf = m->bbuf;
	}
    }
    b->ptr = b->end = b->buf;
    if (b->buf)
	return b->buf;
    return PerlIOBuf_get_base(aTHX_ f);
}

SSize_t
PerlIOMmap_unread(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    PerlIOMmap * const m = PerlIOSelf(f, PerlIOMmap);
    PerlIOBuf * const b = &m->base;
    if (PerlIOBase(f)->flags & PERLIO_F_WRBUF)
	PerlIO_flush(f);
    if (b->ptr && (b->ptr - count) >= b->buf
	&& memEQ(b->ptr - count, vbuf, count)) {
	b->ptr -= count;
	PerlIOBase(f)->flags &= ~PERLIO_F_EOF;
	return count;
    }
    if (m->len) {
	/*
	 * Loose the unwritable mapped buffer
	 */
	PerlIO_flush(f);
	/*
	 * If flush took the "buffer" see if we have one from before
	 */
	if (!b->buf && m->bbuf)
	    b->buf = m->bbuf;
	if (!b->buf) {
	    PerlIOBuf_get_base(aTHX_ f);
	    m->bbuf = b->buf;
	}
    }
    return PerlIOBuf_unread(aTHX_ f, vbuf, count);
}

SSize_t
PerlIOMmap_write(pTHX_ PerlIO *f, const void *vbuf, Size_t count)
{
    PerlIOMmap * const m = PerlIOSelf(f, PerlIOMmap);
    PerlIOBuf * const b = &m->base;

    if (!b->buf || !(PerlIOBase(f)->flags & PERLIO_F_WRBUF)) {
	/*
	 * No, or wrong sort of, buffer
	 */
	if (m->len) {
	    if (PerlIOMmap_unmap(aTHX_ f) != 0)
		return 0;
	}
	/*
	 * If unmap took the "buffer" see if we have one from before
	 */
	if (!b->buf && m->bbuf)
	    b->buf = m->bbuf;
	if (!b->buf) {
	    PerlIOBuf_get_base(aTHX_ f);
	    m->bbuf = b->buf;
	}
    }
    return PerlIOBuf_write(aTHX_ f, vbuf, count);
}

IV
PerlIOMmap_flush(pTHX_ PerlIO *f)
{
    PerlIOMmap * const m = PerlIOSelf(f, PerlIOMmap);
    PerlIOBuf * const b = &m->base;
    IV code = PerlIOBuf_flush(aTHX_ f);
    /*
     * Now we are "synced" at PerlIOBuf level
     */
    if (b->buf) {
	if (m->len) {
	    /*
	     * Unmap the buffer
	     */
	    if (PerlIOMmap_unmap(aTHX_ f) != 0)
		code = -1;
	}
	else {
	    /*
	     * We seem to have a PerlIOBuf buffer which was not mapped
	     * remember it in case we need one later
	     */
	    m->bbuf = b->buf;
	}
    }
    return code;
}

IV
PerlIOMmap_fill(pTHX_ PerlIO *f)
{
    PerlIOBuf * const b = PerlIOSelf(f, PerlIOBuf);
    IV code = PerlIO_flush(f);
    if (code == 0 && !b->buf) {
	code = PerlIOMmap_map(aTHX_ f);
    }
    if (code == 0 && !(PerlIOBase(f)->flags & PERLIO_F_RDBUF)) {
	code = PerlIOBuf_fill(aTHX_ f);
    }
    return code;
}

IV
PerlIOMmap_close(pTHX_ PerlIO *f)
{
    PerlIOMmap * const m = PerlIOSelf(f, PerlIOMmap);
    PerlIOBuf * const b = &m->base;
    IV code = PerlIO_flush(f);
    if (m->bbuf) {
	b->buf = m->bbuf;
	m->bbuf = NULL;
	b->ptr = b->end = b->buf;
    }
    if (PerlIOBuf_close(aTHX_ f) != 0)
	code = -1;
    return code;
}

PerlIO *
PerlIOMmap_dup(pTHX_ PerlIO *f, PerlIO *o, CLONE_PARAMS *param, int flags)
{
 return PerlIOBase_dup(aTHX_ f, o, param, flags);
}


PERLIO_FUNCS_DECL(PerlIO_mmap) = {
    sizeof(PerlIO_funcs),
    "mmap",
    sizeof(PerlIOMmap),
    PERLIO_K_BUFFERED|PERLIO_K_RAW,
    PerlIOBuf_pushed,
    PerlIOBuf_popped,
    PerlIOBuf_open,
    PerlIOBase_binmode,         /* binmode */
    NULL,
    PerlIOBase_fileno,
    PerlIOMmap_dup,
    PerlIOBuf_read,
    PerlIOMmap_unread,
    PerlIOMmap_write,
    PerlIOBuf_seek,
    PerlIOBuf_tell,
    PerlIOBuf_close,
    PerlIOMmap_flush,
    PerlIOMmap_fill,
    PerlIOBase_eof,
    PerlIOBase_error,
    PerlIOBase_clearerr,
    PerlIOBase_setlinebuf,
    PerlIOMmap_get_base,
    PerlIOBuf_bufsiz,
    PerlIOBuf_get_ptr,
    PerlIOBuf_get_cnt,
    PerlIOBuf_set_ptrcnt,
};

#endif                          /* HAS_MMAP */

PerlIO *
Perl_PerlIO_stdin(pTHX)
{
    dVAR;
    if (!PL_perlio) {
	PerlIO_stdstreams(aTHX);
    }
    return &PL_perlio[1];
}

PerlIO *
Perl_PerlIO_stdout(pTHX)
{
    dVAR;
    if (!PL_perlio) {
	PerlIO_stdstreams(aTHX);
    }
    return &PL_perlio[2];
}

PerlIO *
Perl_PerlIO_stderr(pTHX)
{
    dVAR;
    if (!PL_perlio) {
	PerlIO_stdstreams(aTHX);
    }
    return &PL_perlio[3];
}

/*--------------------------------------------------------------------------------------*/

char *
PerlIO_getname(PerlIO *f, char *buf)
{
    dTHX;
#ifdef VMS
    char *name = NULL;
    bool exported = FALSE;
    FILE *stdio = PerlIOSelf(f, PerlIOStdio)->stdio;
    if (!stdio) {
	stdio = PerlIO_exportFILE(f,0);
	exported = TRUE;
    }
    if (stdio) {
	name = fgetname(stdio, buf);
	if (exported) PerlIO_releaseFILE(f,stdio);
    }
    return name;
#else
    PERL_UNUSED_ARG(f);
    PERL_UNUSED_ARG(buf);
    Perl_croak(aTHX_ "Don't know how to get file name");
    return NULL;
#endif
}


/*--------------------------------------------------------------------------------------*/
/*
 * Functions which can be called on any kind of PerlIO implemented in
 * terms of above
 */

#undef PerlIO_fdopen
PerlIO *
PerlIO_fdopen(int fd, const char *mode)
{
    dTHX;
    return PerlIO_openn(aTHX_ NULL, mode, fd, 0, 0, NULL, 0, NULL);
}

#undef PerlIO_open
PerlIO *
PerlIO_open(const char *path, const char *mode)
{
    dTHX;
    SV *name = sv_2mortal(newSVpv(path, 0));
    return PerlIO_openn(aTHX_ NULL, mode, -1, 0, 0, NULL, 1, &name);
}

#undef Perlio_reopen
PerlIO *
PerlIO_reopen(const char *path, const char *mode, PerlIO *f)
{
    dTHX;
    SV *name = sv_2mortal(newSVpv(path,0));
    return PerlIO_openn(aTHX_ NULL, mode, -1, 0, 0, f, 1, &name);
}

#undef PerlIO_getc
int
PerlIO_getc(PerlIO *f)
{
    dTHX;
    STDCHAR buf[1];
    if ( 1 == PerlIO_read(f, buf, 1) ) {
	return (unsigned char) buf[0];
    }
    return EOF;
}

#undef PerlIO_ungetc
int
PerlIO_ungetc(PerlIO *f, int ch)
{
    dTHX;
    if (ch != EOF) {
	STDCHAR buf = ch;
	if (PerlIO_unread(f, &buf, 1) == 1)
	    return ch;
    }
    return EOF;
}

#undef PerlIO_putc
int
PerlIO_putc(PerlIO *f, int ch)
{
    dTHX;
    STDCHAR buf = ch;
    return PerlIO_write(f, &buf, 1);
}

#undef PerlIO_puts
int
PerlIO_puts(PerlIO *f, const char *s)
{
    dTHX;
    return PerlIO_write(f, s, strlen(s));
}

#undef PerlIO_rewind
void
PerlIO_rewind(PerlIO *f)
{
    dTHX;
    PerlIO_seek(f, (Off_t) 0, SEEK_SET);
    PerlIO_clearerr(f);
}

#undef PerlIO_vprintf
int
PerlIO_vprintf(PerlIO *f, const char *fmt, va_list ap)
{
    dTHX;
    SV * sv;
    const char *s;
    STRLEN len;
    SSize_t wrote;
#ifdef NEED_VA_COPY
    va_list apc;
    Perl_va_copy(ap, apc);
    sv = vnewSVpvf(fmt, &apc);
#else
    sv = vnewSVpvf(fmt, &ap);
#endif
    s = SvPV_const(sv, len);
    wrote = PerlIO_write(f, s, len);
    SvREFCNT_dec(sv);
    return wrote;
}

#undef PerlIO_printf
int
PerlIO_printf(PerlIO *f, const char *fmt, ...)
{
    va_list ap;
    int result;
    va_start(ap, fmt);
    result = PerlIO_vprintf(f, fmt, ap);
    va_end(ap);
    return result;
}

#undef PerlIO_stdoutf
int
PerlIO_stdoutf(const char *fmt, ...)
{
    dTHX;
    va_list ap;
    int result;
    va_start(ap, fmt);
    result = PerlIO_vprintf(PerlIO_stdout(), fmt, ap);
    va_end(ap);
    return result;
}

#undef PerlIO_tmpfile
PerlIO *
PerlIO_tmpfile(void)
{
     dTHX;
     PerlIO *f = NULL;
#ifdef WIN32
     const int fd = win32_tmpfd();
     if (fd >= 0)
	  f = PerlIO_fdopen(fd, "w+b");
#else /* WIN32 */
#    if defined(HAS_MKSTEMP) && ! defined(VMS) && ! defined(OS2)
     SV * const sv = newSVpvs("/tmp/PerlIO_XXXXXX");
     /*
      * I have no idea how portable mkstemp() is ... NI-S
      */
     const int fd = mkstemp(SvPVX(sv));
     if (fd >= 0) {
	  f = PerlIO_fdopen(fd, "w+");
	  if (f)
	       PerlIOBase(f)->flags |= PERLIO_F_TEMP;
	  PerlLIO_unlink(SvPVX_const(sv));
     }
     SvREFCNT_dec(sv);
#    else	/* !HAS_MKSTEMP, fallback to stdio tmpfile(). */
     FILE * const stdio = PerlSIO_tmpfile();

     if (stdio)
	  f = PerlIO_fdopen(fileno(stdio), "w+");

#    endif /* else HAS_MKSTEMP */
#endif /* else WIN32 */
     return f;
}

#undef HAS_FSETPOS
#undef HAS_FGETPOS

#endif                          /* USE_SFIO */
#endif                          /* PERLIO_IS_STDIO */

/*======================================================================================*/
/*
 * Now some functions in terms of above which may be needed even if we are
 * not in true PerlIO mode
 */
const char *
Perl_PerlIO_context_layers(pTHX_ const char *mode)
{
    dVAR;
    const char *direction = NULL;
    SV *layers;
    /*
     * Need to supply default layer info from open.pm
     */

    if (!PL_curcop)
	return NULL;

    if (mode && mode[0] != 'r') {
	if (PL_curcop->cop_hints & HINT_LEXICAL_IO_OUT)
	    direction = "open>";
    } else {
	if (PL_curcop->cop_hints & HINT_LEXICAL_IO_IN)
	    direction = "open<";
    }
    if (!direction)
	return NULL;

    layers = Perl_refcounted_he_fetch(aTHX_ PL_curcop->cop_hints_hash,
				      0, direction, 5, 0, 0);

    assert(layers);
    return SvOK(layers) ? SvPV_nolen_const(layers) : NULL;
}


#ifndef HAS_FSETPOS
#undef PerlIO_setpos
int
PerlIO_setpos(PerlIO *f, SV *pos)
{
    dTHX;
    if (SvOK(pos)) {
	STRLEN len;
	const Off_t * const posn = (Off_t *) SvPV(pos, len);
	if (f && len == sizeof(Off_t))
	    return PerlIO_seek(f, *posn, SEEK_SET);
    }
    SETERRNO(EINVAL, SS_IVCHAN);
    return -1;
}
#else
#undef PerlIO_setpos
int
PerlIO_setpos(PerlIO *f, SV *pos)
{
    dTHX;
    if (SvOK(pos)) {
	STRLEN len;
	Fpos_t * const fpos = (Fpos_t *) SvPV(pos, len);
	if (f && len == sizeof(Fpos_t)) {
#if defined(USE_64_BIT_STDIO) && defined(USE_FSETPOS64)
	    return fsetpos64(f, fpos);
#else
	    return fsetpos(f, fpos);
#endif
	}
    }
    SETERRNO(EINVAL, SS_IVCHAN);
    return -1;
}
#endif

#ifndef HAS_FGETPOS
#undef PerlIO_getpos
int
PerlIO_getpos(PerlIO *f, SV *pos)
{
    dTHX;
    Off_t posn = PerlIO_tell(f);
    sv_setpvn(pos, (char *) &posn, sizeof(posn));
    return (posn == (Off_t) - 1) ? -1 : 0;
}
#else
#undef PerlIO_getpos
int
PerlIO_getpos(PerlIO *f, SV *pos)
{
    dTHX;
    Fpos_t fpos;
    int code;
#if defined(USE_64_BIT_STDIO) && defined(USE_FSETPOS64)
    code = fgetpos64(f, &fpos);
#else
    code = fgetpos(f, &fpos);
#endif
    sv_setpvn(pos, (char *) &fpos, sizeof(fpos));
    return code;
}
#endif

#if (defined(PERLIO_IS_STDIO) || !defined(USE_SFIO)) && !defined(HAS_VPRINTF)

int
vprintf(char *pat, char *args)
{
    _doprnt(pat, args, stdout);
    return 0;                   /* wrong, but perl doesn't use the return
				 * value */
}

int
vfprintf(FILE *fd, char *pat, char *args)
{
    _doprnt(pat, args, fd);
    return 0;                   /* wrong, but perl doesn't use the return
				 * value */
}

#endif

#ifndef PerlIO_vsprintf
int
PerlIO_vsprintf(char *s, int n, const char *fmt, va_list ap)
{
    dTHX; 
    const int val = my_vsnprintf(s, n > 0 ? n : 0, fmt, ap);
    PERL_UNUSED_CONTEXT;

#ifndef PERL_MY_VSNPRINTF_GUARDED
    if (val < 0 || (n > 0 ? val >= n : 0)) {
	Perl_croak(aTHX_ "panic: my_vsnprintf overflow in PerlIO_vsprintf\n");
    }
#endif
    return val;
}
#endif

#ifndef PerlIO_sprintf
int
PerlIO_sprintf(char *s, int n, const char *fmt, ...)
{
    va_list ap;
    int result;
    va_start(ap, fmt);
    result = PerlIO_vsprintf(s, n, fmt, ap);
    va_end(ap);
    return result;
}
#endif

/*
 * Local variables:
 * c-indentation-style: bsd
 * c-basic-offset: 4
 * indent-tabs-mode: t
 * End:
 *
 * ex: set ts=8 sts=4 sw=4 noet:
 */