473 lines
11 KiB
C
473 lines
11 KiB
C
/*
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* Copyright (c) 1990 Jan-Simon Pendry
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* Copyright (c) 1990 Imperial College of Science, Technology & Medicine
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* Copyright (c) 1990, 1993
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* The Regents of the University of California. All rights reserved.
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*
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* This code is derived from software contributed to Berkeley by
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* Jan-Simon Pendry at Imperial College, London.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the University of
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* California, Berkeley and its contributors.
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* 4. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* @(#)mtab_file.c 8.1 (Berkeley) 6/6/93
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*
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* $Id$
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*
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*/
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#include "am.h"
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#ifdef READ_MTAB_FROM_FILE
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#ifdef USE_FCNTL
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#include <fcntl.h>
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#else
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#include <sys/file.h>
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#endif /* USE_FCNTL */
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#ifdef UPDATE_MTAB
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/*
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* Do strict /etc/mtab locking
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*/
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#define MTAB_LOCKING
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/*
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* Firewall mtab entries
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*/
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#define MTAB_STRIPNL
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#include <sys/stat.h>
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static FILE *mnt_file;
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/*
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* If the system is being trashed by something, then
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* opening mtab may fail with ENFILE. So, go to sleep
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* for a second and try again. (Yes - this has happened to me.)
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*
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* Note that this *may* block the automounter, oh well.
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* If we get to this state then things are badly wrong anyway...
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*
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* Give the system 10 seconds to recover but then give up.
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* Hopefully something else will exit and free up some file
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* table slots in that time.
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*/
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#define NFILE_RETRIES 10 /* seconds */
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#ifdef MTAB_LOCKING
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#ifdef LOCK_FCNTL
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static int lock(fd)
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{
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int rc;
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struct flock lk;
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lk.l_type = F_WRLCK;
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lk.l_whence = 0;
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lk.l_start = 0;
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lk.l_len = 0;
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again:
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rc = fcntl(fd, F_SETLKW, (caddr_t) &lk);
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if (rc < 0 && (errno == EACCES || errno == EAGAIN)) {
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#ifdef DEBUG
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dlog("Blocked, trying to obtain exclusive mtab lock");
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#endif /* DEBUG */
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sleep(1);
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goto again;
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}
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return rc;
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}
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#else
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#define lock(fd) (flock((fd), LOCK_EX))
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#endif /* LOCK_FCNTL */
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#endif /* MTAB_LOCKING */
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static FILE *open_locked_mtab(mtab_file, mode, fs)
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char *mtab_file;
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char *mode;
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char *fs;
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{
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FILE *mfp = 0;
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#ifdef UPDATE_MTAB
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/*
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* There is a possible race condition if two processes enter
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* this routine at the same time. One will be blocked by the
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* exclusive lock below (or by the shared lock in setmntent)
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* and by the time the second process has the exclusive lock
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* it will be on the wrong underlying object. To check for this
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* the mtab file is stat'ed before and after all the locking
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* sequence, and if it is a different file then we assume that
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* it may be the wrong file (only "may", since there is another
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* race between the initial stat and the setmntent).
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*
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* Simpler solutions to this problem are invited...
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*/
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int racing = 2;
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#ifdef MTAB_LOCKING
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int rc;
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int retries = 0;
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struct stat st_before, st_after;
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#endif /* MTAB_LOCKING */
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if (mnt_file) {
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#ifdef DEBUG
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dlog("Forced close on %s in read_mtab", mtab_file);
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#endif /* DEBUG */
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endmntent(mnt_file);
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mnt_file = 0;
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}
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#ifdef MTAB_LOCKING
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again:
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if (mfp) {
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endmntent(mfp);
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mfp = 0;
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}
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clock_valid = 0;
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if (stat(mtab_file, &st_before) < 0) {
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plog(XLOG_ERROR, "%s: stat: %m", mtab_file);
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if (errno == ESTALE) {
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/* happens occasionally */
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sleep(1);
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goto again;
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}
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return 0;
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}
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#endif /* MTAB_LOCKING */
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#endif /* UPDATE_MTAB */
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eacces:
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mfp = setmntent(mtab_file, mode);
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if (!mfp) {
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/*
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* Since setmntent locks the descriptor, it
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* is possible it can fail... so retry if
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* needed.
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*/
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if (errno == EACCES || errno == EAGAIN) {
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#ifdef DEBUG
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dlog("Blocked, trying to obtain exclusive mtab lock");
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#endif /* DEBUG */
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goto eacces;
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} else if (errno == ENFILE && retries++ < NFILE_RETRIES) {
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sleep(1);
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goto eacces;
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}
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plog(XLOG_ERROR, "setmntent(\"%s\", \"%s\"): %m", mtab_file, mode);
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return 0;
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}
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#ifdef MTAB_LOCKING
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#ifdef UPDATE_MTAB
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/*
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* At this point we have an exclusive lock on the mount list,
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* but it may be the wrong one so...
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*/
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/*
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* Need to get an exclusive lock on the current
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* mount table until we have a new copy written
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* out, when the lock is released in free_mntlist.
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* flock is good enough since the mount table is
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* not shared between machines.
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*/
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do
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rc = lock(fileno(mfp));
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while (rc < 0 && errno == EINTR);
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if (rc < 0) {
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plog(XLOG_ERROR, "Couldn't lock %s: %m", mtab_file);
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endmntent(mfp);
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return 0;
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}
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/*
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* Now check whether the mtab file has changed under our feet
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*/
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if (stat(mtab_file, &st_after) < 0) {
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plog(XLOG_ERROR, "%s: stat", mtab_file);
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goto again;
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}
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if (st_before.st_dev != st_after.st_dev ||
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st_before.st_ino != st_after.st_ino) {
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struct timeval tv;
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if (racing == 0) {
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/* Sometimes print a warning */
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plog(XLOG_WARNING,
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"Possible mount table race - retrying %s", fs);
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}
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racing = (racing+1) & 3;
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/*
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* Take a nap. From: Doug Kingston <dpk@morgan.com>
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*/
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tv.tv_sec = 0;
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tv.tv_usec = (mypid & 0x07) << 17;
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if (tv.tv_usec)
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if (select(0, (voidp) 0, (voidp) 0, (voidp) 0, &tv) < 0)
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plog(XLOG_WARNING, "mtab nap failed: %m");
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goto again;
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}
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#endif /* UPDATE_MTAB */
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#endif /* MTAB_LOCKING */
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return mfp;
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}
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/*
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* Unlock the mount table
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*/
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void unlock_mntlist P((void));
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void unlock_mntlist()
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{
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/*
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* Release file lock, by closing the file
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*/
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if (mnt_file) {
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endmntent(mnt_file);
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mnt_file = 0;
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}
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}
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/*
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* Write out a mount list
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*/
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void rewrite_mtab(mp)
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mntlist *mp;
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{
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FILE *mfp;
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int error = 0;
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/*
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* Concoct a temporary name in the same
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* directory as the target mount table
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* so that rename() will work.
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*/
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char tmpname[64];
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int retries;
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int tmpfd;
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char *cp;
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char *mcp = mtab;
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cp = strrchr(mcp, '/');
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if (cp) {
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bcopy(mcp, tmpname, cp - mcp);
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tmpname[cp-mcp] = '\0';
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} else {
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plog(XLOG_WARNING, "No '/' in mtab (%s), using \".\" as tmp directory", mtab);
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tmpname[0] = '.'; tmpname[1] = '\0';
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}
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strcat(tmpname, "/mtabXXXXXX");
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mktemp(tmpname);
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retries = 0;
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enfile1:
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if ((tmpfd = open(tmpname, O_RDWR|O_CREAT|O_TRUNC, 0644)) < 0) {
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if (errno == ENFILE && retries++ < NFILE_RETRIES) {
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sleep(1);
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goto enfile1;
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}
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plog(XLOG_ERROR, "%s: open: %m", tmpname);
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return;
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}
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if (close(tmpfd) < 0)
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plog(XLOG_ERROR, "Couldn't close tmp file descriptor: %m");
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retries = 0;
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enfile2:
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mfp = setmntent(tmpname, "w");
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if (!mfp) {
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if (errno == ENFILE && retries++ < NFILE_RETRIES) {
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sleep(1);
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goto enfile2;
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}
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plog(XLOG_ERROR, "setmntent(\"%s\", \"w\"): %m", tmpname);
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error = 1;
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goto out;
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}
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while (mp) {
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if (mp->mnt) {
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if (addmntent(mfp, mp->mnt)) {
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plog(XLOG_ERROR, "Can't write entry to %s", tmpname);
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error = 1;
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goto out;
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}
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}
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mp = mp->mnext;
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}
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/*
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* SunOS 4.1 manuals say that the return code from entmntent()
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* is always 1 and to treat as a void. That means we need to
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* call fflush() to make sure the new mtab file got written.
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*/
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if (fflush(mfp)) {
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plog(XLOG_ERROR, "flush new mtab file: %m");
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error = 1;
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goto out;
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}
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(void) endmntent(mfp);
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/*
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* Rename temporary mtab to real mtab
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*/
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if (rename(tmpname, mtab) < 0) {
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plog(XLOG_ERROR, "rename %s to %s: %m", tmpname, mtab);
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error = 1;
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goto out;
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}
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out:
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if (error)
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(void) unlink(tmpname);
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}
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#ifdef MTAB_STRIPNL
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static void mtab_stripnl(s)
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char *s;
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{
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do {
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s = strchr(s, '\n');
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if (s)
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*s++ = ' ';
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} while (s);
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}
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#endif /* MTAB_STRIPNL */
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/*
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* Append a mntent structure to the
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* current mount table.
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*/
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void write_mntent(mp)
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struct mntent *mp;
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{
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int retries = 0;
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FILE *mfp;
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enfile:
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mfp = open_locked_mtab(mtab, "a", mp->mnt_dir);
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if (mfp) {
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#ifdef MTAB_STRIPNL
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mtab_stripnl(mp->mnt_opts);
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#endif /* MTAB_STRIPNL */
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if (addmntent(mfp, mp))
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plog(XLOG_ERROR, "Couldn't write %s: %m", mtab);
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if (fflush(mfp))
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plog(XLOG_ERROR, "Couldn't flush %s: %m", mtab);
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(void) endmntent(mfp);
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} else {
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if (errno == ENFILE && retries < NFILE_RETRIES) {
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sleep(1);
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goto enfile;
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}
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plog(XLOG_ERROR, "setmntent(\"%s\", \"a\"): %m", mtab);
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}
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}
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#endif /* UPDATE_MTAB */
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static struct mntent *mnt_dup(mp)
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struct mntent *mp;
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{
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struct mntent *new_mp = ALLOC(mntent);
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new_mp->mnt_fsname = strdup(mp->mnt_fsname);
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new_mp->mnt_dir = strdup(mp->mnt_dir);
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new_mp->mnt_type = strdup(mp->mnt_type);
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new_mp->mnt_opts = strdup(mp->mnt_opts);
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new_mp->mnt_freq = mp->mnt_freq;
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new_mp->mnt_passno = mp->mnt_passno;
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#ifdef FIXUP_MNTENT_DUP
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/*
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* Additional fields get dup'ed here
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*/
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FIXUP_MNTENT_DUP(new_mp, mp);
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#endif
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return new_mp;
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}
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/*
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* Read a mount table into memory
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*/
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mntlist *read_mtab(fs)
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char *fs;
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{
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mntlist **mpp, *mhp;
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struct mntent *mep;
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FILE *mfp = open_locked_mtab(mtab, "r+", fs);
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if (!mfp)
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return 0;
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mpp = &mhp;
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/*
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* XXX - In SunOS 4 there is (yet another) memory leak
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* which loses 1K the first time getmntent is called.
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* (jsp)
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*/
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while (mep = getmntent(mfp)) {
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/*
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* Allocate a new slot
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*/
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*mpp = ALLOC(mntlist);
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/*
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* Copy the data returned by getmntent
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*/
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(*mpp)->mnt = mnt_dup(mep);
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/*
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* Move to next pointer
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*/
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mpp = &(*mpp)->mnext;
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}
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*mpp = 0;
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#ifdef UPDATE_MTAB
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/*
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* If we are not updating the mount table then we
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* can free the resources held here, otherwise they
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* must be held until the mount table update is complete
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*/
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mnt_file = mfp;
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#else
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endmntent(mfp);
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#endif /* UPDATE_MTAB */
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return mhp;
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}
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#endif /* READ_MTAB_FROM_FILE */
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