[asperl] add AS patch#21 (misc. fixes)

[p5sagit/p5-mst-13.2.git] / doio.c

/*    doio.c
 *
 *    Copyright (c) 1991-1997, Larry Wall
 *
 *    You may distribute under the terms of either the GNU General Public
 *    License or the Artistic License, as specified in the README file.
 *
 */

/*
 * "Far below them they saw the white waters pour into a foaming bowl, and
 * then swirl darkly about a deep oval basin in the rocks, until they found
 * their way out again through a narrow gate, and flowed away, fuming and
 * chattering, into calmer and more level reaches."
 */

#include "EXTERN.h"
#include "perl.h"

#if defined(HAS_MSG) || defined(HAS_SEM) || defined(HAS_SHM)
#include <sys/ipc.h>
#ifdef HAS_MSG
#include <sys/msg.h>
#endif
#ifdef HAS_SEM
#include <sys/sem.h>
#endif
#ifdef HAS_SHM
#include <sys/shm.h>
# ifndef HAS_SHMAT_PROTOTYPE
    extern Shmat_t shmat _((int, char *, int));
# endif
#endif
#endif

#ifdef I_UTIME
#  if defined(_MSC_VER) || defined(__MINGW32__)
#    include <sys/utime.h>
#  else
#    include <utime.h>
#  endif
#endif

#ifdef I_FCNTL
#include <fcntl.h>
#endif
#ifdef I_SYS_FILE
#include <sys/file.h>
#endif
#ifdef O_EXCL
#  define OPEN_EXCL O_EXCL
#else
#  define OPEN_EXCL 0
#endif

#if !defined(NSIG) || defined(M_UNIX) || defined(M_XENIX)
#include <signal.h>
#endif

/* XXX If this causes problems, set i_unistd=undef in the hint file.  */
#ifdef I_UNISTD
#  include <unistd.h>
#endif

#if defined(HAS_SOCKET) && !defined(VMS) /* VMS handles sockets via vmsish.h */
# include <sys/socket.h>
# include <netdb.h>
# ifndef ENOTSOCK
#  ifdef I_NET_ERRNO
#   include <net/errno.h>
#  endif
# endif
#endif

/* Put this after #includes because <unistd.h> defines _XOPEN_*. */
#ifndef Sock_size_t
#  if _XOPEN_VERSION >= 5 || defined(_XOPEN_SOURCE_EXTENDED) || defined(__GLIBC__)
#    define Sock_size_t Size_t
#  else
#    define Sock_size_t int
#  endif
#endif

bool
do_open(GV *gv, register char *name, I32 len, int as_raw, int rawmode, int rawperm, PerlIO *supplied_fp)
{
    register IO *io = GvIOn(gv);
    PerlIO *saveifp = Nullfp;
    PerlIO *saveofp = Nullfp;
    char savetype = ' ';
    int writing = 0;
    PerlIO *fp;
    int fd;
    int result;
    bool was_fdopen = FALSE;

    forkprocess = 1;		/* assume true if no fork */

    if (IoIFP(io)) {
	fd = PerlIO_fileno(IoIFP(io));
	if (IoTYPE(io) == '-')
	    result = 0;
	else if (fd <= maxsysfd) {
	    saveifp = IoIFP(io);
	    saveofp = IoOFP(io);
	    savetype = IoTYPE(io);
	    result = 0;
	}
	else if (IoTYPE(io) == '|')
	    result = PerlProc_pclose(IoIFP(io));
	else if (IoIFP(io) != IoOFP(io)) {
	    if (IoOFP(io)) {
		result = PerlIO_close(IoOFP(io));
		PerlIO_close(IoIFP(io));	/* clear stdio, fd already closed */
	    }
	    else
		result = PerlIO_close(IoIFP(io));
	}
	else
	    result = PerlIO_close(IoIFP(io));
	if (result == EOF && fd > maxsysfd)
	    PerlIO_printf(PerlIO_stderr(), "Warning: unable to close filehandle %s properly.\n",
	      GvENAME(gv));
	IoOFP(io) = IoIFP(io) = Nullfp;
    }

    if (as_raw) {
	result = rawmode & 3;
	IoTYPE(io) = "<>++"[result];
	writing = (result > 0);
	fd = PerlLIO_open3(name, rawmode, rawperm);
	if (fd == -1)
	    fp = NULL;
	else {
	    char *fpmode;
	    if (result == 0)
		fpmode = "r";
#ifdef O_APPEND
	    else if (rawmode & O_APPEND)
		fpmode = (result == 1) ? "a" : "a+";
#endif
	    else
		fpmode = (result == 1) ? "w" : "r+";
	    fp = PerlIO_fdopen(fd, fpmode);
	    if (!fp)
		PerlLIO_close(fd);
	}
    }
    else {
	char *myname;
	char mode[3];		/* stdio file mode ("r\0" or "r+\0") */
	int dodup;

	myname = savepvn(name, len);
	SAVEFREEPV(myname);
	name = myname;
	while (len && isSPACE(name[len-1]))
	    name[--len] = '\0';

	mode[0] = mode[1] = mode[2] = '\0';
	IoTYPE(io) = *name;
	if (*name == '+' && len > 1 && name[len-1] != '|') { /* scary */
	    mode[1] = *name++;
	    --len;
	    writing = 1;
	}

	if (*name == '|') {
	    /*SUPPRESS 530*/
	    for (name++; isSPACE(*name); name++) ;
	    if (strNE(name,"-"))
		TAINT_ENV();
	    TAINT_PROPER("piped open");
	    if (name[strlen(name)-1] == '|') {
		name[strlen(name)-1] = '\0' ;
		if (dowarn)
		    warn("Can't do bidirectional pipe");
	    }
	    fp = PerlProc_popen(name,"w");
	    writing = 1;
	}
	else if (*name == '>') {
	    TAINT_PROPER("open");
	    name++;
	    if (*name == '>') {
		mode[0] = IoTYPE(io) = 'a';
		name++;
	    }
	    else
		mode[0] = 'w';
	    writing = 1;

	    if (*name == '&') {
	      duplicity:
		dodup = 1;
		name++;
		if (*name == '=') {
		    dodup = 0;
		    name++;
		}
		if (!*name && supplied_fp)
		    fp = supplied_fp;
		else {
		    /*SUPPRESS 530*/
		    for (; isSPACE(*name); name++) ;
		    if (isDIGIT(*name))
			fd = atoi(name);
		    else {
			IO* thatio;
			gv = gv_fetchpv(name,FALSE,SVt_PVIO);
			thatio = GvIO(gv);
			if (!thatio) {
#ifdef EINVAL
			    SETERRNO(EINVAL,SS$_IVCHAN);
#endif
			    goto say_false;
			}
			if (IoIFP(thatio)) {
			    fd = PerlIO_fileno(IoIFP(thatio));
			    if (IoTYPE(thatio) == 's')
				IoTYPE(io) = 's';
			}
			else
			    fd = -1;
		    }
		    if (dodup)
			fd = PerlLIO_dup(fd);
		    else
			was_fdopen = TRUE;
		    if (!(fp = PerlIO_fdopen(fd,mode))) {
			if (dodup)
			    PerlLIO_close(fd);
			}
		}
	    }
	    else {
		/*SUPPRESS 530*/
		for (; isSPACE(*name); name++) ;
		if (strEQ(name,"-")) {
		    fp = PerlIO_stdout();
		    IoTYPE(io) = '-';
		}
		else  {
		    fp = PerlIO_open(name,mode);
		}
	    }
	}
	else if (*name == '<') {
	    /*SUPPRESS 530*/
	    for (name++; isSPACE(*name); name++) ;
	    mode[0] = 'r';
	    if (*name == '&')
		goto duplicity;
	    if (strEQ(name,"-")) {
		fp = PerlIO_stdin();
		IoTYPE(io) = '-';
	    }
	    else
		fp = PerlIO_open(name,mode);
	}
	else if (name[len-1] == '|') {
	    name[--len] = '\0';
	    while (len && isSPACE(name[len-1]))
		name[--len] = '\0';
	    /*SUPPRESS 530*/
	    for (; isSPACE(*name); name++) ;
	    if (strNE(name,"-"))
		TAINT_ENV();
	    TAINT_PROPER("piped open");
	    fp = PerlProc_popen(name,"r");
	    IoTYPE(io) = '|';
	}
	else {
	    IoTYPE(io) = '<';
	    /*SUPPRESS 530*/
	    for (; isSPACE(*name); name++) ;
	    if (strEQ(name,"-")) {
		fp = PerlIO_stdin();
		IoTYPE(io) = '-';
	    }
	    else
		fp = PerlIO_open(name,"r");
	}
    }
    if (!fp) {
	if (dowarn && IoTYPE(io) == '<' && strchr(name, '\n'))
	    warn(warn_nl, "open");
	goto say_false;
    }
    if (IoTYPE(io) &&
      IoTYPE(io) != '|' && IoTYPE(io) != '-') {
	dTHR;
	if (PerlLIO_fstat(PerlIO_fileno(fp),&statbuf) < 0) {
	    (void)PerlIO_close(fp);
	    goto say_false;
	}
	if (S_ISSOCK(statbuf.st_mode))
	    IoTYPE(io) = 's';	/* in case a socket was passed in to us */
#ifdef HAS_SOCKET
	else if (
#ifdef S_IFMT
	    !(statbuf.st_mode & S_IFMT)
#else
	    !statbuf.st_mode
#endif
	) {
	    char tmpbuf[256];
	    Sock_size_t buflen = sizeof tmpbuf;
	    if (PerlSock_getsockname(PerlIO_fileno(fp), (struct sockaddr *)tmpbuf,
			    &buflen) >= 0
		  || errno != ENOTSOCK)
		IoTYPE(io) = 's'; /* some OS's return 0 on fstat()ed socket */
				/* but some return 0 for streams too, sigh */
	}
#endif
    }
    if (saveifp) {		/* must use old fp? */
	fd = PerlIO_fileno(saveifp);
	if (saveofp) {
	    PerlIO_flush(saveofp);		/* emulate PerlIO_close() */
	    if (saveofp != saveifp) {	/* was a socket? */
		PerlIO_close(saveofp);
		if (fd > 2)
		    Safefree(saveofp);
	    }
	}
	if (fd != PerlIO_fileno(fp)) {
	    int pid;
	    SV *sv;

	    PerlLIO_dup2(PerlIO_fileno(fp), fd);
	    sv = *av_fetch(fdpid,PerlIO_fileno(fp),TRUE);
	    (void)SvUPGRADE(sv, SVt_IV);
	    pid = SvIVX(sv);
	    SvIVX(sv) = 0;
	    sv = *av_fetch(fdpid,fd,TRUE);
	    (void)SvUPGRADE(sv, SVt_IV);
	    SvIVX(sv) = pid;
	    if (!was_fdopen)
		PerlIO_close(fp);

	}
	fp = saveifp;
	PerlIO_clearerr(fp);
    }
#if defined(HAS_FCNTL) && defined(F_SETFD)
    fd = PerlIO_fileno(fp);
    fcntl(fd,F_SETFD,fd > maxsysfd);
#endif
    IoIFP(io) = fp;
    if (writing) {
	dTHR;
	if (IoTYPE(io) == 's'
	  || (IoTYPE(io) == '>' && S_ISCHR(statbuf.st_mode)) ) {
	    if (!(IoOFP(io) = PerlIO_fdopen(PerlIO_fileno(fp),"w"))) {
		PerlIO_close(fp);
		IoIFP(io) = Nullfp;
		goto say_false;
	    }
	}
	else
	    IoOFP(io) = fp;
    }
    return TRUE;

say_false:
    IoIFP(io) = saveifp;
    IoOFP(io) = saveofp;
    IoTYPE(io) = savetype;
    return FALSE;
}

PerlIO *
nextargv(register GV *gv)
{
    register SV *sv;
#ifndef FLEXFILENAMES
    int filedev;
    int fileino;
#endif
    int fileuid;
    int filegid;

    if (!argvoutgv)
	argvoutgv = gv_fetchpv("ARGVOUT",TRUE,SVt_PVIO);
    if (filemode & (S_ISUID|S_ISGID)) {
	PerlIO_flush(IoIFP(GvIOn(argvoutgv)));  /* chmod must follow last write */
#ifdef HAS_FCHMOD
	(void)fchmod(lastfd,filemode);
#else
	(void)PerlLIO_chmod(oldname,filemode);
#endif
    }
    filemode = 0;
    while (av_len(GvAV(gv)) >= 0) {
	dTHR;
	STRLEN oldlen;
	sv = av_shift(GvAV(gv));
	SAVEFREESV(sv);
	sv_setsv(GvSV(gv),sv);
	SvSETMAGIC(GvSV(gv));
	oldname = SvPVx(GvSV(gv), oldlen);
	if (do_open(gv,oldname,oldlen,inplace!=0,0,0,Nullfp)) {
	    if (inplace) {
		TAINT_PROPER("inplace open");
		if (oldlen == 1 && *oldname == '-') {
		    setdefout(gv_fetchpv("STDOUT",TRUE,SVt_PVIO));
		    return IoIFP(GvIOp(gv));
		}
#ifndef FLEXFILENAMES
		filedev = statbuf.st_dev;
		fileino = statbuf.st_ino;
#endif
		filemode = statbuf.st_mode;
		fileuid = statbuf.st_uid;
		filegid = statbuf.st_gid;
		if (!S_ISREG(filemode)) {
		    warn("Can't do inplace edit: %s is not a regular file",
		      oldname );
		    do_close(gv,FALSE);
		    continue;
		}
		if (*inplace) {
#ifdef SUFFIX
		    add_suffix(sv,inplace);
#else
		    sv_catpv(sv,inplace);
#endif
#ifndef FLEXFILENAMES
		    if (PerlLIO_stat(SvPVX(sv),&statbuf) >= 0
		      && statbuf.st_dev == filedev
		      && statbuf.st_ino == fileino
#ifdef DJGPP
                      || (_djstat_fail_bits & _STFAIL_TRUENAME)!=0
#endif
                      ) {
			warn("Can't do inplace edit: %s would not be uniq",
			  SvPVX(sv) );
			do_close(gv,FALSE);
			continue;
		    }
#endif
#ifdef HAS_RENAME
#ifndef DOSISH
		    if (PerlLIO_rename(oldname,SvPVX(sv)) < 0) {
			warn("Can't rename %s to %s: %s, skipping file",
			  oldname, SvPVX(sv), Strerror(errno) );
			do_close(gv,FALSE);
			continue;
		    }
#else
		    do_close(gv,FALSE);
		    (void)PerlLIO_unlink(SvPVX(sv));
		    (void)PerlLIO_rename(oldname,SvPVX(sv));
		    do_open(gv,SvPVX(sv),SvCUR(sv),inplace!=0,0,0,Nullfp);
#endif /* DOSISH */
#else
		    (void)UNLINK(SvPVX(sv));
		    if (link(oldname,SvPVX(sv)) < 0) {
			warn("Can't rename %s to %s: %s, skipping file",
			  oldname, SvPVX(sv), Strerror(errno) );
			do_close(gv,FALSE);
			continue;
		    }
		    (void)UNLINK(oldname);
#endif
		}
		else {
#if !defined(DOSISH) && !defined(AMIGAOS)
#  ifndef VMS  /* Don't delete; use automatic file versioning */
		    if (UNLINK(oldname) < 0) {
			warn("Can't remove %s: %s, skipping file",
			  oldname, Strerror(errno) );
			do_close(gv,FALSE);
			continue;
		    }
#  endif
#else
		    croak("Can't do inplace edit without backup");
#endif
		}

		sv_setpvn(sv,">",!inplace);
		sv_catpvn(sv,oldname,oldlen);
		SETERRNO(0,0);		/* in case sprintf set errno */
		if (!do_open(argvoutgv,SvPVX(sv),SvCUR(sv),inplace!=0,
			     O_WRONLY|O_CREAT|OPEN_EXCL,0666,Nullfp)) {
		    warn("Can't do inplace edit on %s: %s",
		      oldname, Strerror(errno) );
		    do_close(gv,FALSE);
		    continue;
		}
		setdefout(argvoutgv);
		lastfd = PerlIO_fileno(IoIFP(GvIOp(argvoutgv)));
		(void)PerlLIO_fstat(lastfd,&statbuf);
#ifdef HAS_FCHMOD
		(void)fchmod(lastfd,filemode);
#else
#  if !(defined(WIN32) && defined(__BORLANDC__))
		/* Borland runtime creates a readonly file! */
		(void)PerlLIO_chmod(oldname,filemode);
#  endif
#endif
		if (fileuid != statbuf.st_uid || filegid != statbuf.st_gid) {
#ifdef HAS_FCHOWN
		    (void)fchown(lastfd,fileuid,filegid);
#else
#ifdef HAS_CHOWN
		    (void)PerlLIO_chown(oldname,fileuid,filegid);
#endif
#endif
		}
	    }
	    return IoIFP(GvIOp(gv));
	}
	else
	    PerlIO_printf(PerlIO_stderr(), "Can't open %s: %s\n",
	      SvPV(sv, na), Strerror(errno));
    }
    if (inplace) {
	(void)do_close(argvoutgv,FALSE);
	setdefout(gv_fetchpv("STDOUT",TRUE,SVt_PVIO));
    }
    return Nullfp;
}

#ifdef HAS_PIPE
void
do_pipe(SV *sv, GV *rgv, GV *wgv)
{
    register IO *rstio;
    register IO *wstio;
    int fd[2];

    if (!rgv)
	goto badexit;
    if (!wgv)
	goto badexit;

    rstio = GvIOn(rgv);
    wstio = GvIOn(wgv);

    if (IoIFP(rstio))
	do_close(rgv,FALSE);
    if (IoIFP(wstio))
	do_close(wgv,FALSE);

    if (PerlProc_pipe(fd) < 0)
	goto badexit;
    IoIFP(rstio) = PerlIO_fdopen(fd[0], "r");
    IoOFP(wstio) = PerlIO_fdopen(fd[1], "w");
    IoIFP(wstio) = IoOFP(wstio);
    IoTYPE(rstio) = '<';
    IoTYPE(wstio) = '>';
    if (!IoIFP(rstio) || !IoOFP(wstio)) {
	if (IoIFP(rstio)) PerlIO_close(IoIFP(rstio));
	else PerlLIO_close(fd[0]);
	if (IoOFP(wstio)) PerlIO_close(IoOFP(wstio));
	else PerlLIO_close(fd[1]);
	goto badexit;
    }

    sv_setsv(sv,&sv_yes);
    return;

badexit:
    sv_setsv(sv,&sv_undef);
    return;
}
#endif

/* explicit renamed to avoid C++ conflict    -- kja */
bool
do_close(GV *gv, bool not_implicit)
{
    bool retval;
    IO *io;

    if (!gv)
	gv = argvgv;
    if (!gv || SvTYPE(gv) != SVt_PVGV) {
	SETERRNO(EBADF,SS$_IVCHAN);
	return FALSE;
    }
    io = GvIO(gv);
    if (!io) {		/* never opened */
	if (dowarn && not_implicit)
	    warn("Close on unopened file <%s>",GvENAME(gv));
	SETERRNO(EBADF,SS$_IVCHAN);
	return FALSE;
    }
    retval = io_close(io);
    if (not_implicit) {
	IoLINES(io) = 0;
	IoPAGE(io) = 0;
	IoLINES_LEFT(io) = IoPAGE_LEN(io);
    }
    IoTYPE(io) = ' ';
    return retval;
}

bool
io_close(IO *io)
{
    bool retval = FALSE;
    int status;

    if (IoIFP(io)) {
	if (IoTYPE(io) == '|') {
	    status = PerlProc_pclose(IoIFP(io));
	    STATUS_NATIVE_SET(status);
	    retval = (STATUS_POSIX == 0);
	}
	else if (IoTYPE(io) == '-')
	    retval = TRUE;
	else {
	    if (IoOFP(io) && IoOFP(io) != IoIFP(io)) {		/* a socket */
		retval = (PerlIO_close(IoOFP(io)) != EOF);
		PerlIO_close(IoIFP(io));	/* clear stdio, fd already closed */
	    }
	    else
		retval = (PerlIO_close(IoIFP(io)) != EOF);
	}
	IoOFP(io) = IoIFP(io) = Nullfp;
    }
    else {
	SETERRNO(EBADF,SS$_IVCHAN);
    }

    return retval;
}

bool
do_eof(GV *gv)
{
    dTHR;
    register IO *io;
    int ch;

    io = GvIO(gv);

    if (!io)
	return TRUE;

    while (IoIFP(io)) {

        if (PerlIO_has_cntptr(IoIFP(io))) {	/* (the code works without this) */
	    if (PerlIO_get_cnt(IoIFP(io)) > 0)	/* cheat a little, since */
		return FALSE;			/* this is the most usual case */
        }

	ch = PerlIO_getc(IoIFP(io));
	if (ch != EOF) {
	    (void)PerlIO_ungetc(IoIFP(io),ch);
	    return FALSE;
	}
        if (PerlIO_has_cntptr(IoIFP(io)) && PerlIO_canset_cnt(IoIFP(io))) {
	    if (PerlIO_get_cnt(IoIFP(io)) < -1)
		PerlIO_set_cnt(IoIFP(io),-1);
	}
	if (op->op_flags & OPf_SPECIAL) { /* not necessarily a real EOF yet? */
	    if (!nextargv(argvgv))	/* get another fp handy */
		return TRUE;
	}
	else
	    return TRUE;		/* normal fp, definitely end of file */
    }
    return TRUE;
}

long
do_tell(GV *gv)
{
    register IO *io;
    register PerlIO *fp;

    if (gv && (io = GvIO(gv)) && (fp = IoIFP(io))) {
#ifdef ULTRIX_STDIO_BOTCH
	if (PerlIO_eof(fp))
	    (void)PerlIO_seek(fp, 0L, 2);	/* ultrix 1.2 workaround */
#endif
	return PerlIO_tell(fp);
    }
    if (dowarn)
	warn("tell() on unopened file");
    SETERRNO(EBADF,RMS$_IFI);
    return -1L;
}

bool
do_seek(GV *gv, long int pos, int whence)
{
    register IO *io;
    register PerlIO *fp;

    if (gv && (io = GvIO(gv)) && (fp = IoIFP(io))) {
#ifdef ULTRIX_STDIO_BOTCH
	if (PerlIO_eof(fp))
	    (void)PerlIO_seek(fp, 0L, 2);	/* ultrix 1.2 workaround */
#endif
	return PerlIO_seek(fp, pos, whence) >= 0;
    }
    if (dowarn)
	warn("seek() on unopened file");
    SETERRNO(EBADF,RMS$_IFI);
    return FALSE;
}

long
do_sysseek(GV *gv, long int pos, int whence)
{
    register IO *io;
    register PerlIO *fp;

    if (gv && (io = GvIO(gv)) && (fp = IoIFP(io)))
	return PerlLIO_lseek(PerlIO_fileno(fp), pos, whence);
    if (dowarn)
	warn("sysseek() on unopened file");
    SETERRNO(EBADF,RMS$_IFI);
    return -1L;
}

int
do_binmode(PerlIO *fp, int iotype, int flag)
{
    if (flag != TRUE)
	croak("panic: unsetting binmode"); /* Not implemented yet */
#ifdef DOSISH
#ifdef atarist
    if (!PerlIO_flush(fp) && (fp->_flag |= _IOBIN))
	return 1;
    else
	return 0;
#else
    if (PerlLIO_setmode(PerlIO_fileno(fp), OP_BINARY) != -1) {
#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
	 */
	PerlIO_seek(fp,0L,0);
	((FILE*)fp)->flags |= _F_BIN;
#endif
	return 1;
    }
    else
	return 0;
#endif
#else
#if defined(USEMYBINMODE)
    if (my_binmode(fp,iotype) != NULL)
	return 1;
    else
	return 0;
#else
    return 1;
#endif
#endif
}

#if !defined(HAS_TRUNCATE) && !defined(HAS_CHSIZE) && defined(F_FREESP)
	/* code courtesy of William Kucharski */
#define HAS_CHSIZE

I32 my_chsize(fd, length)
I32 fd;			/* file descriptor */
Off_t length;		/* length to set file to */
{
    struct flock fl;
    struct stat filebuf;

    if (PerlLIO_fstat(fd, &filebuf) < 0)
	return -1;

    if (filebuf.st_size < length) {

	/* extend file length */

	if ((PerlLIO_lseek(fd, (length - 1), 0)) < 0)
	    return -1;

	/* write a "0" byte */

	if ((PerlLIO_write(fd, "", 1)) != 1)
	    return -1;
    }
    else {
	/* truncate length */

	fl.l_whence = 0;
	fl.l_len = 0;
	fl.l_start = length;
	fl.l_type = F_WRLCK;    /* write lock on file space */

	/*
	* This relies on the UNDOCUMENTED F_FREESP argument to
	* fcntl(2), which truncates the file so that it ends at the
	* position indicated by fl.l_start.
	*
	* Will minor miracles never cease?
	*/

	if (fcntl(fd, F_FREESP, &fl) < 0)
	    return -1;

    }

    return 0;
}
#endif /* F_FREESP */

bool
do_print(register SV *sv, PerlIO *fp)
{
    register char *tmps;
    STRLEN len;

    /* assuming fp is checked earlier */
    if (!sv)
	return TRUE;
    if (ofmt) {
	if (SvGMAGICAL(sv))
	    mg_get(sv);
        if (SvIOK(sv) && SvIVX(sv) != 0) {
	    PerlIO_printf(fp, ofmt, (double)SvIVX(sv));
	    return !PerlIO_error(fp);
	}
	if (  (SvNOK(sv) && SvNVX(sv) != 0.0)
	   || (looks_like_number(sv) && sv_2nv(sv) != 0.0) ) {
	    PerlIO_printf(fp, ofmt, SvNVX(sv));
	    return !PerlIO_error(fp);
	}
    }
    switch (SvTYPE(sv)) {
    case SVt_NULL:
	if (dowarn)
	    warn(warn_uninit);
	return TRUE;
    case SVt_IV:
	if (SvIOK(sv)) {
	    if (SvGMAGICAL(sv))
		mg_get(sv);
	    PerlIO_printf(fp, "%ld", (long)SvIVX(sv));
	    return !PerlIO_error(fp);
	}
	/* FALL THROUGH */
    default:
	tmps = SvPV(sv, len);
	break;
    }
    if (len && (PerlIO_write(fp,tmps,len) == 0 || PerlIO_error(fp)))
	return FALSE;
    return !PerlIO_error(fp);
}

I32
my_stat(ARGSproto)
{
    djSP;
    IO *io;
    GV* tmpgv;

    if (op->op_flags & OPf_REF) {
	EXTEND(SP,1);
	tmpgv = cGVOP->op_gv;
      do_fstat:
	io = GvIO(tmpgv);
	if (io && IoIFP(io)) {
	    statgv = tmpgv;
	    sv_setpv(statname,"");
	    laststype = OP_STAT;
	    return (laststatval = PerlLIO_fstat(PerlIO_fileno(IoIFP(io)), &statcache));
	}
	else {
	    if (tmpgv == defgv)
		return laststatval;
	    if (dowarn)
		warn("Stat on unopened file <%s>",
		  GvENAME(tmpgv));
	    statgv = Nullgv;
	    sv_setpv(statname,"");
	    return (laststatval = -1);
	}
    }
    else {
	SV* sv = POPs;
	char *s;
	PUTBACK;
	if (SvTYPE(sv) == SVt_PVGV) {
	    tmpgv = (GV*)sv;
	    goto do_fstat;
	}
	else if (SvROK(sv) && SvTYPE(SvRV(sv)) == SVt_PVGV) {
	    tmpgv = (GV*)SvRV(sv);
	    goto do_fstat;
	}

	s = SvPV(sv, na);
	statgv = Nullgv;
	sv_setpv(statname, s);
	laststype = OP_STAT;
	laststatval = PerlLIO_stat(s, &statcache);
	if (laststatval < 0 && dowarn && strchr(s, '\n'))
	    warn(warn_nl, "stat");
	return laststatval;
    }
}

I32
my_lstat(ARGSproto)
{
    djSP;
    SV *sv;
    if (op->op_flags & OPf_REF) {
	EXTEND(SP,1);
	if (cGVOP->op_gv == defgv) {
	    if (laststype != OP_LSTAT)
		croak("The stat preceding -l _ wasn't an lstat");
	    return laststatval;
	}
	croak("You can't use -l on a filehandle");
    }

    laststype = OP_LSTAT;
    statgv = Nullgv;
    sv = POPs;
    PUTBACK;
    sv_setpv(statname,SvPV(sv, na));
#ifdef HAS_LSTAT
    laststatval = PerlLIO_lstat(SvPV(sv, na),&statcache);
#else
    laststatval = PerlLIO_stat(SvPV(sv, na),&statcache);
#endif
    if (laststatval < 0 && dowarn && strchr(SvPV(sv, na), '\n'))
	warn(warn_nl, "lstat");
    return laststatval;
}

bool
do_aexec(SV *really, register SV **mark, register SV **sp)
{
    register char **a;
    char *tmps;

    if (sp > mark) {
	dTHR;
	New(401,Argv, sp - mark + 1, char*);
	a = Argv;
	while (++mark <= sp) {
	    if (*mark)
		*a++ = SvPVx(*mark, na);
	    else
		*a++ = "";
	}
	*a = Nullch;
	if (*Argv[0] != '/')	/* will execvp use PATH? */
	    TAINT_ENV();		/* testing IFS here is overkill, probably */
	if (really && *(tmps = SvPV(really, na)))
	    PerlProc_execvp(tmps,Argv);
	else
	    PerlProc_execvp(Argv[0],Argv);
	if (dowarn)
	    warn("Can't exec \"%s\": %s", Argv[0], Strerror(errno));
    }
    do_execfree();
    return FALSE;
}

void
do_execfree(void)
{
    if (Argv) {
	Safefree(Argv);
	Argv = Null(char **);
    }
    if (Cmd) {
	Safefree(Cmd);
	Cmd = Nullch;
    }
}

#if !defined(OS2) && !defined(WIN32) && !defined(DJGPP)

bool
do_exec(char *cmd)
{
    register char **a;
    register char *s;
    char flags[10];

    while (*cmd && isSPACE(*cmd))
	cmd++;

    /* save an extra exec if possible */

#ifdef CSH
    if (strnEQ(cmd,cshname,cshlen) && strnEQ(cmd+cshlen," -c",3)) {
	strcpy(flags,"-c");
	s = cmd+cshlen+3;
	if (*s == 'f') {
	    s++;
	    strcat(flags,"f");
	}
	if (*s == ' ')
	    s++;
	if (*s++ == '\'') {
	    char *ncmd = s;

	    while (*s)
		s++;
	    if (s[-1] == '\n')
		*--s = '\0';
	    if (s[-1] == '\'') {
		*--s = '\0';
		PerlProc_execl(cshname,"csh", flags,ncmd,(char*)0);
		*s = '\'';
		return FALSE;
	    }
	}
    }
#endif /* CSH */

    /* see if there are shell metacharacters in it */

    if (*cmd == '.' && isSPACE(cmd[1]))
	goto doshell;

    if (strnEQ(cmd,"exec",4) && isSPACE(cmd[4]))
	goto doshell;

    for (s = cmd; *s && isALPHA(*s); s++) ;	/* catch VAR=val gizmo */
    if (*s == '=')
	goto doshell;

    for (s = cmd; *s; s++) {
	if (*s != ' ' && !isALPHA(*s) && strchr("$&*(){}[]'\";\\|?<>~`\n",*s)) {
	    if (*s == '\n' && !s[1]) {
		*s = '\0';
		break;
	    }
	  doshell:
	    PerlProc_execl(sh_path, "sh", "-c", cmd, (char*)0);
	    return FALSE;
	}
    }

    New(402,Argv, (s - cmd) / 2 + 2, char*);
    Cmd = savepvn(cmd, s-cmd);
    a = Argv;
    for (s = Cmd; *s;) {
	while (*s && isSPACE(*s)) s++;
	if (*s)
	    *(a++) = s;
	while (*s && !isSPACE(*s)) s++;
	if (*s)
	    *s++ = '\0';
    }
    *a = Nullch;
    if (Argv[0]) {
	PerlProc_execvp(Argv[0],Argv);
	if (errno == ENOEXEC) {		/* for system V NIH syndrome */
	    do_execfree();
	    goto doshell;
	}
	if (dowarn)
	    warn("Can't exec \"%s\": %s", Argv[0], Strerror(errno));
    }
    do_execfree();
    return FALSE;
}

#endif /* OS2 || WIN32 */

I32
apply(I32 type, register SV **mark, register SV **sp)
{
    dTHR;
    register I32 val;
    register I32 val2;
    register I32 tot = 0;
    char *what;
    char *s;
    SV **oldmark = mark;

#define APPLY_TAINT_PROPER() \
    STMT_START {						\
	if (tainting && tainted) { goto taint_proper_label; }	\
    } STMT_END

    /* This is a first heuristic; it doesn't catch tainting magic. */
    if (tainting) {
	while (++mark <= sp) {
	    if (SvTAINTED(*mark)) {
		TAINT;
		break;
	    }
	}
	mark = oldmark;
    }
    switch (type) {
    case OP_CHMOD:
	what = "chmod";
	APPLY_TAINT_PROPER();
	if (++mark <= sp) {
	    val = SvIVx(*mark);
	    APPLY_TAINT_PROPER();
	    tot = sp - mark;
	    while (++mark <= sp) {
		char *name = SvPVx(*mark, na);
		APPLY_TAINT_PROPER();
		if (PerlLIO_chmod(name, val))
		    tot--;
	    }
	}
	break;
#ifdef HAS_CHOWN
    case OP_CHOWN:
	what = "chown";
	APPLY_TAINT_PROPER();
	if (sp - mark > 2) {
	    val = SvIVx(*++mark);
	    val2 = SvIVx(*++mark);
	    APPLY_TAINT_PROPER();
	    tot = sp - mark;
	    while (++mark <= sp) {
		char *name = SvPVx(*mark, na);
		APPLY_TAINT_PROPER();
		if (PerlLIO_chown(name, val, val2))
		    tot--;
	    }
	}
	break;
#endif
#ifdef HAS_KILL
    case OP_KILL:
	what = "kill";
	APPLY_TAINT_PROPER();
	if (mark == sp)
	    break;
	s = SvPVx(*++mark, na);
	if (isUPPER(*s)) {
	    if (*s == 'S' && s[1] == 'I' && s[2] == 'G')
		s += 3;
	    if (!(val = whichsig(s)))
		croak("Unrecognized signal name \"%s\"",s);
	}
	else
	    val = SvIVx(*mark);
	APPLY_TAINT_PROPER();
	tot = sp - mark;
#ifdef VMS
	/* kill() doesn't do process groups (job trees?) under VMS */
	if (val < 0) val = -val;
	if (val == SIGKILL) {
#	    include <starlet.h>
	    /* Use native sys$delprc() to insure that target process is
	     * deleted; supervisor-mode images don't pay attention to
	     * CRTL's emulation of Unix-style signals and kill()
	     */
	    while (++mark <= sp) {
		I32 proc = SvIVx(*mark);
		register unsigned long int __vmssts;
		APPLY_TAINT_PROPER();
		if (!((__vmssts = sys$delprc(&proc,0)) & 1)) {
		    tot--;
		    switch (__vmssts) {
			case SS$_NONEXPR:
			case SS$_NOSUCHNODE:
			    SETERRNO(ESRCH,__vmssts);
			    break;
			case SS$_NOPRIV:
			    SETERRNO(EPERM,__vmssts);
			    break;
			default:
			    SETERRNO(EVMSERR,__vmssts);
		    }
		}
	    }
	    break;
	}
#endif
	if (val < 0) {
	    val = -val;
	    while (++mark <= sp) {
		I32 proc = SvIVx(*mark);
		APPLY_TAINT_PROPER();
#ifdef HAS_KILLPG
		if (PerlProc_killpg(proc,val))	/* BSD */
#else
		if (PerlProc_kill(-proc,val))	/* SYSV */
#endif
		    tot--;
	    }
	}
	else {
	    while (++mark <= sp) {
		I32 proc = SvIVx(*mark);
		APPLY_TAINT_PROPER();
		if (PerlProc_kill(proc, val))
		    tot--;
	    }
	}
	break;
#endif
    case OP_UNLINK:
	what = "unlink";
	APPLY_TAINT_PROPER();
	tot = sp - mark;
	while (++mark <= sp) {
	    s = SvPVx(*mark, na);
	    APPLY_TAINT_PROPER();
	    if (euid || unsafe) {
		if (UNLINK(s))
		    tot--;
	    }
	    else {	/* don't let root wipe out directories without -U */
#ifdef HAS_LSTAT
		if (PerlLIO_lstat(s,&statbuf) < 0 || S_ISDIR(statbuf.st_mode))
#else
		if (PerlLIO_stat(s,&statbuf) < 0 || S_ISDIR(statbuf.st_mode))
#endif
		    tot--;
		else {
		    if (UNLINK(s))
			tot--;
		}
	    }
	}
	break;
#ifdef HAS_UTIME
    case OP_UTIME:
	what = "utime";
	APPLY_TAINT_PROPER();
	if (sp - mark > 2) {
#if defined(I_UTIME) || defined(VMS)
	    struct utimbuf utbuf;
#else
	    struct {
		long    actime;
		long	modtime;
	    } utbuf;
#endif

	    Zero(&utbuf, sizeof utbuf, char);
#ifdef BIG_TIME
	    utbuf.actime = (Time_t)SvNVx(*++mark);    /* time accessed */
	    utbuf.modtime = (Time_t)SvNVx(*++mark);    /* time modified */
#else
	    utbuf.actime = SvIVx(*++mark);    /* time accessed */
	    utbuf.modtime = SvIVx(*++mark);    /* time modified */
#endif
	    APPLY_TAINT_PROPER();
	    tot = sp - mark;
	    while (++mark <= sp) {
		char *name = SvPVx(*mark, na);
		APPLY_TAINT_PROPER();
		if (PerlLIO_utime(name, &utbuf))
		    tot--;
	    }
	}
	else
	    tot = 0;
	break;
#endif
    }
    return tot;

  taint_proper_label:
    TAINT_PROPER(what);
    return 0;	/* this should never happen */

#undef APPLY_TAINT_PROPER
}

/* Do the permissions allow some operation?  Assumes statcache already set. */
#ifndef VMS /* VMS' cando is in vms.c */
I32
cando(I32 bit, I32 effective, register struct stat *statbufp)
{
#ifdef DOSISH
    /* [Comments and code from Len Reed]
     * MS-DOS "user" is similar to UNIX's "superuser," but can't write
     * to write-protected files.  The execute permission bit is set
     * by the Miscrosoft C library stat() function for the following:
     *		.exe files
     *		.com files
     *		.bat files
     *		directories
     * All files and directories are readable.
     * Directories and special files, e.g. "CON", cannot be
     * write-protected.
     * [Comment by Tom Dinger -- a directory can have the write-protect
     *		bit set in the file system, but DOS permits changes to
     *		the directory anyway.  In addition, all bets are off
     *		here for networked software, such as Novell and
     *		Sun's PC-NFS.]
     */

     /* Atari stat() does pretty much the same thing. we set x_bit_set_in_stat
      * too so it will actually look into the files for magic numbers
      */
     return (bit & statbufp->st_mode) ? TRUE : FALSE;

#else /* ! DOSISH */
    if ((effective ? euid : uid) == 0) {	/* root is special */
	if (bit == S_IXUSR) {
	    if (statbufp->st_mode & 0111 || S_ISDIR(statbufp->st_mode))
		return TRUE;
	}
	else
	    return TRUE;		/* root reads and writes anything */
	return FALSE;
    }
    if (statbufp->st_uid == (effective ? euid : uid) ) {
	if (statbufp->st_mode & bit)
	    return TRUE;	/* ok as "user" */
    }
    else if (ingroup((I32)statbufp->st_gid,effective)) {
	if (statbufp->st_mode & bit >> 3)
	    return TRUE;	/* ok as "group" */
    }
    else if (statbufp->st_mode & bit >> 6)
	return TRUE;	/* ok as "other" */
    return FALSE;
#endif /* ! DOSISH */
}
#endif /* ! VMS */

I32
ingroup(I32 testgid, I32 effective)
{
    if (testgid == (effective ? egid : gid))
	return TRUE;
#ifdef HAS_GETGROUPS
#ifndef NGROUPS
#define NGROUPS 32
#endif
    {
	Groups_t gary[NGROUPS];
	I32 anum;

	anum = getgroups(NGROUPS,gary);
	while (--anum >= 0)
	    if (gary[anum] == testgid)
		return TRUE;
    }
#endif
    return FALSE;
}

#if defined(HAS_MSG) || defined(HAS_SEM) || defined(HAS_SHM)

I32
do_ipcget(I32 optype, SV **mark, SV **sp)
{
    dTHR;
    key_t key;
    I32 n, flags;

    key = (key_t)SvNVx(*++mark);
    n = (optype == OP_MSGGET) ? 0 : SvIVx(*++mark);
    flags = SvIVx(*++mark);
    SETERRNO(0,0);
    switch (optype)
    {
#ifdef HAS_MSG
    case OP_MSGGET:
	return msgget(key, flags);
#endif
#ifdef HAS_SEM
    case OP_SEMGET:
	return semget(key, n, flags);
#endif
#ifdef HAS_SHM
    case OP_SHMGET:
	return shmget(key, n, flags);
#endif
#if !defined(HAS_MSG) || !defined(HAS_SEM) || !defined(HAS_SHM)
    default:
	croak("%s not implemented", op_desc[optype]);
#endif
    }
    return -1;			/* should never happen */
}

#if defined(__sun) && defined(__svr4__) /* XXX Need metaconfig test */
/* Solaris manpage says that it uses (like linux)
   int semctl (int semid, int semnum, int cmd, union semun arg)
   but the system include files do not define union semun !!!!
   Note: Linux/glibc *does* declare union semun in <sys/sem_buf.h>
   but, unlike the older Linux libc and Solaris, it has an extra
   struct seminfo * on the end.
*/
union semun {
     int val;
     struct semid_ds *buf;
     ushort *array;
};
#endif

I32
do_ipcctl(I32 optype, SV **mark, SV **sp)
{
    dTHR;
    SV *astr;
    char *a;
    I32 id, n, cmd, infosize, getinfo;
    I32 ret = -1;
/* XXX REALLY need metaconfig test */
/* linux and Solaris2 use:
   int semctl (int semid, int semnum, int cmd, union semun arg)
   instead of:
   int semctl (int semid, int semnum, int cmd, struct semid_ds *arg);
   Solaris and Linux (pre-glibc) use
       union semun {
            int val;
            struct semid_ds *buf;
            ushort *array;
       };
   but Solaris doesn't declare it in a header file (we declared it
   explicitly earlier). Linux/glibc declares a *different* union semun
   so we just refer to "union semun" here.
    
*/
#if defined(__linux__) || (defined(__sun__) && defined(__svr4__))
#   define SEMCTL_SEMUN
    union semun unsemds, semun;
#endif

    id = SvIVx(*++mark);
    n = (optype == OP_SEMCTL) ? SvIVx(*++mark) : 0;
    cmd = SvIVx(*++mark);
    astr = *++mark;
    infosize = 0;
    getinfo = (cmd == IPC_STAT);

    switch (optype)
    {
#ifdef HAS_MSG
    case OP_MSGCTL:
	if (cmd == IPC_STAT || cmd == IPC_SET)
	    infosize = sizeof(struct msqid_ds);
	break;
#endif
#ifdef HAS_SHM
    case OP_SHMCTL:
	if (cmd == IPC_STAT || cmd == IPC_SET)
	    infosize = sizeof(struct shmid_ds);
	break;
#endif
#ifdef HAS_SEM
    case OP_SEMCTL:
	if (cmd == IPC_STAT || cmd == IPC_SET)
	    infosize = sizeof(struct semid_ds);
	else if (cmd == GETALL || cmd == SETALL)
	{
	    struct semid_ds semds;
#ifdef SEMCTL_SEMUN
            semun.buf = &semds;
	    if (semctl(id, 0, IPC_STAT, semun) == -1)
#else
	    if (semctl(id, 0, IPC_STAT, &semds) == -1)
#endif
		return -1;
	    getinfo = (cmd == GETALL);
	    infosize = semds.sem_nsems * sizeof(short);
		/* "short" is technically wrong but much more portable
		   than guessing about u_?short(_t)? */
	}
	break;
#endif
#if !defined(HAS_MSG) || !defined(HAS_SEM) || !defined(HAS_SHM)
    default:
	croak("%s not implemented", op_desc[optype]);
#endif
    }

    if (infosize)
    {
	STRLEN len;
	if (getinfo)
	{
	    SvPV_force(astr, len);
	    a = SvGROW(astr, infosize+1);
	}
	else
	{
	    a = SvPV(astr, len);
	    if (len != infosize)
		croak("Bad arg length for %s, is %lu, should be %ld",
			op_desc[optype], (unsigned long)len, (long)infosize);
	}
    }
    else
    {
	IV i = SvIV(astr);
	a = (char *)i;		/* ouch */
    }
    SETERRNO(0,0);
    switch (optype)
    {
#ifdef HAS_MSG
    case OP_MSGCTL:
	ret = msgctl(id, cmd, (struct msqid_ds *)a);
	break;
#endif
#ifdef HAS_SEM
    case OP_SEMCTL:
#ifdef SEMCTL_SEMUN
	/* XXX Need metaconfig test */
        unsemds.buf = (struct semid_ds *)a;
	ret = semctl(id, n, cmd, unsemds);
#else
	ret = semctl(id, n, cmd, (struct semid_ds *)a);
#endif
	break;
#endif
#ifdef HAS_SHM
    case OP_SHMCTL:
	ret = shmctl(id, cmd, (struct shmid_ds *)a);
	break;
#endif
    }
    if (getinfo && ret >= 0) {
	SvCUR_set(astr, infosize);
	*SvEND(astr) = '\0';
	SvSETMAGIC(astr);
    }
    return ret;
}

I32
do_msgsnd(SV **mark, SV **sp)
{
#ifdef HAS_MSG
    dTHR;
    SV *mstr;
    char *mbuf;
    I32 id, msize, flags;
    STRLEN len;

    id = SvIVx(*++mark);
    mstr = *++mark;
    flags = SvIVx(*++mark);
    mbuf = SvPV(mstr, len);
    if ((msize = len - sizeof(long)) < 0)
	croak("Arg too short for msgsnd");
    SETERRNO(0,0);
    return msgsnd(id, (struct msgbuf *)mbuf, msize, flags);
#else
    croak("msgsnd not implemented");
#endif
}

I32
do_msgrcv(SV **mark, SV **sp)
{
#ifdef HAS_MSG
    dTHR;
    SV *mstr;
    char *mbuf;
    long mtype;
    I32 id, msize, flags, ret;
    STRLEN len;

    id = SvIVx(*++mark);
    mstr = *++mark;
    msize = SvIVx(*++mark);
    mtype = (long)SvIVx(*++mark);
    flags = SvIVx(*++mark);
    if (SvTHINKFIRST(mstr)) {
	if (SvREADONLY(mstr))
	    croak("Can't msgrcv to readonly var");
	if (SvROK(mstr))
	    sv_unref(mstr);
    }
    SvPV_force(mstr, len);
    mbuf = SvGROW(mstr, sizeof(long)+msize+1);
    
    SETERRNO(0,0);
    ret = msgrcv(id, (struct msgbuf *)mbuf, msize, mtype, flags);
    if (ret >= 0) {
	SvCUR_set(mstr, sizeof(long)+ret);
	*SvEND(mstr) = '\0';
    }
    return ret;
#else
    croak("msgrcv not implemented");
#endif
}

I32
do_semop(SV **mark, SV **sp)
{
#ifdef HAS_SEM
    dTHR;
    SV *opstr;
    char *opbuf;
    I32 id;
    STRLEN opsize;

    id = SvIVx(*++mark);
    opstr = *++mark;
    opbuf = SvPV(opstr, opsize);
    if (opsize < sizeof(struct sembuf)
	|| (opsize % sizeof(struct sembuf)) != 0) {
	SETERRNO(EINVAL,LIB$_INVARG);
	return -1;
    }
    SETERRNO(0,0);
    return semop(id, (struct sembuf *)opbuf, opsize/sizeof(struct sembuf));
#else
    croak("semop not implemented");
#endif
}

I32
do_shmio(I32 optype, SV **mark, SV **sp)
{
#ifdef HAS_SHM
    dTHR;
    SV *mstr;
    char *mbuf, *shm;
    I32 id, mpos, msize;
    STRLEN len;
    struct shmid_ds shmds;

    id = SvIVx(*++mark);
    mstr = *++mark;
    mpos = SvIVx(*++mark);
    msize = SvIVx(*++mark);
    SETERRNO(0,0);
    if (shmctl(id, IPC_STAT, &shmds) == -1)
	return -1;
    if (mpos < 0 || msize < 0 || mpos + msize > shmds.shm_segsz) {
	SETERRNO(EFAULT,SS$_ACCVIO);		/* can't do as caller requested */
	return -1;
    }
    shm = (char *)shmat(id, (char*)NULL, (optype == OP_SHMREAD) ? SHM_RDONLY : 0);
    if (shm == (char *)-1)	/* I hate System V IPC, I really do */
	return -1;
    if (optype == OP_SHMREAD) {
	SvPV_force(mstr, len);
	mbuf = SvGROW(mstr, msize+1);

	Copy(shm + mpos, mbuf, msize, char);
	SvCUR_set(mstr, msize);
	*SvEND(mstr) = '\0';
	SvSETMAGIC(mstr);
    }
    else {
	I32 n;

	mbuf = SvPV(mstr, len);
	if ((n = len) > msize)
	    n = msize;
	Copy(mbuf, shm + mpos, n, char);
	if (n < msize)
	    memzero(shm + mpos + n, msize - n);
    }
    return shmdt(shm);
#else
    croak("shm I/O not implemented");
#endif
}

#endif /* SYSV IPC */