Annotation of src/lib/libc/stdio/freopen.c, revision 1.1

1.1     ! dillon      1: /*-
        !             2:  * Copyright (c) 1990, 1993
        !             3:  *     The Regents of the University of California.  All rights reserved.
        !             4:  *
        !             5:  * This code is derived from software contributed to Berkeley by
        !             6:  * Chris Torek.
        !             7:  *
        !             8:  * Redistribution and use in source and binary forms, with or without
        !             9:  * modification, are permitted provided that the following conditions
        !            10:  * are met:
        !            11:  * 1. Redistributions of source code must retain the above copyright
        !            12:  *    notice, this list of conditions and the following disclaimer.
        !            13:  * 2. Redistributions in binary form must reproduce the above copyright
        !            14:  *    notice, this list of conditions and the following disclaimer in the
        !            15:  *    documentation and/or other materials provided with the distribution.
        !            16:  * 3. All advertising materials mentioning features or use of this software
        !            17:  *    must display the following acknowledgement:
        !            18:  *     This product includes software developed by the University of
        !            19:  *     California, Berkeley and its contributors.
        !            20:  * 4. Neither the name of the University nor the names of its contributors
        !            21:  *    may be used to endorse or promote products derived from this software
        !            22:  *    without specific prior written permission.
        !            23:  *
        !            24:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            25:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            26:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            27:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            28:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            29:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            30:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            31:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            32:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            33:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            34:  * SUCH DAMAGE.
        !            35:  */
        !            36: 
        !            37: #if defined(LIBC_SCCS) && !defined(lint)
        !            38: #if 0
        !            39: static char sccsid[] = "@(#)freopen.c  8.1 (Berkeley) 6/4/93";
        !            40: #endif
        !            41: static const char rcsid[] =
        !            42:     "$FreeBSD: src/lib/libc/stdio/freopen.c,v 1.5.2.1 2001/03/05 10:54:53 obrien Exp $";
        !            43: #endif /* LIBC_SCCS and not lint */
        !            44: 
        !            45: #include <sys/types.h>
        !            46: #include <sys/stat.h>
        !            47: #include <fcntl.h>
        !            48: #include <errno.h>
        !            49: #include <unistd.h>
        !            50: #include <stdio.h>
        !            51: #include <stdlib.h>
        !            52: #include "libc_private.h"
        !            53: #include "local.h"
        !            54: 
        !            55: /*
        !            56:  * Re-direct an existing, open (probably) file to some other file.
        !            57:  * ANSI is written such that the original file gets closed if at
        !            58:  * all possible, no matter what.
        !            59:  */
        !            60: FILE *
        !            61: freopen(file, mode, fp)
        !            62:        const char *file, *mode;
        !            63:        FILE *fp;
        !            64: {
        !            65:        int f;
        !            66:        int flags, isopen, oflags, sverrno, wantfd;
        !            67: 
        !            68:        if ((flags = __sflags(mode, &oflags)) == 0) {
        !            69:                (void) fclose(fp);
        !            70:                return (NULL);
        !            71:        }
        !            72: 
        !            73:        FLOCKFILE(fp);
        !            74: 
        !            75:        if (!__sdidinit)
        !            76:                __sinit();
        !            77: 
        !            78:        /*
        !            79:         * There are actually programs that depend on being able to "freopen"
        !            80:         * descriptors that weren't originally open.  Keep this from breaking.
        !            81:         * Remember whether the stream was open to begin with, and which file
        !            82:         * descriptor (if any) was associated with it.  If it was attached to
        !            83:         * a descriptor, defer closing it; freopen("/dev/stdin", "r", stdin)
        !            84:         * should work.  This is unnecessary if it was not a Unix file.
        !            85:         */
        !            86:        if (fp->_flags == 0) {
        !            87:                fp->_flags = __SEOF;    /* hold on to it */
        !            88:                isopen = 0;
        !            89:                wantfd = -1;
        !            90:        } else {
        !            91:                /* flush the stream; ANSI doesn't require this. */
        !            92:                if (fp->_flags & __SWR)
        !            93:                        (void) __sflush(fp);
        !            94:                /* if close is NULL, closing is a no-op, hence pointless */
        !            95:                isopen = fp->_close != NULL;
        !            96:                if ((wantfd = fp->_file) < 0 && isopen) {
        !            97:                        (void) (*fp->_close)(fp->_cookie);
        !            98:                        isopen = 0;
        !            99:                }
        !           100:        }
        !           101: 
        !           102:        /* Get a new descriptor to refer to the new file. */
        !           103:        f = _open(file, oflags, DEFFILEMODE);
        !           104:        if (f < 0 && isopen) {
        !           105:                /* If out of fd's close the old one and try again. */
        !           106:                if (errno == ENFILE || errno == EMFILE) {
        !           107:                        (void) (*fp->_close)(fp->_cookie);
        !           108:                        isopen = 0;
        !           109:                        f = _open(file, oflags, DEFFILEMODE);
        !           110:                }
        !           111:        }
        !           112:        sverrno = errno;
        !           113: 
        !           114:        /*
        !           115:         * Finish closing fp.  Even if the open succeeded above, we cannot
        !           116:         * keep fp->_base: it may be the wrong size.  This loses the effect
        !           117:         * of any setbuffer calls, but stdio has always done this before.
        !           118:         */
        !           119:        if (isopen)
        !           120:                (void) (*fp->_close)(fp->_cookie);
        !           121:        if (fp->_flags & __SMBF)
        !           122:                free((char *)fp->_bf._base);
        !           123:        fp->_w = 0;
        !           124:        fp->_r = 0;
        !           125:        fp->_p = NULL;
        !           126:        fp->_bf._base = NULL;
        !           127:        fp->_bf._size = 0;
        !           128:        fp->_lbfsize = 0;
        !           129:        if (HASUB(fp))
        !           130:                FREEUB(fp);
        !           131:        fp->_ub._size = 0;
        !           132:        if (HASLB(fp))
        !           133:                FREELB(fp);
        !           134:        fp->_lb._size = 0;
        !           135: 
        !           136:        if (f < 0) {                    /* did not get it after all */
        !           137:                fp->_flags = 0;         /* set it free */
        !           138:                errno = sverrno;        /* restore in case _close clobbered */
        !           139:                FUNLOCKFILE(fp);
        !           140:                return (NULL);
        !           141:        }
        !           142: 
        !           143:        /*
        !           144:         * If reopening something that was open before on a real file, try
        !           145:         * to maintain the descriptor.  Various C library routines (perror)
        !           146:         * assume stderr is always fd STDERR_FILENO, even if being freopen'd.
        !           147:         */
        !           148:        if (wantfd >= 0 && f != wantfd) {
        !           149:                if (dup2(f, wantfd) >= 0) {
        !           150:                        (void)_close(f);
        !           151:                        f = wantfd;
        !           152:                }
        !           153:        }
        !           154: 
        !           155:        fp->_flags = flags;
        !           156:        fp->_file = f;
        !           157:        fp->_cookie = fp;
        !           158:        fp->_read = __sread;
        !           159:        fp->_write = __swrite;
        !           160:        fp->_seek = __sseek;
        !           161:        fp->_close = __sclose;
        !           162:        FUNLOCKFILE(fp);
        !           163:        return (fp);
        !           164: }