usr/src/usr.sbin/amd/config/mtab_file.c

/*
 * Copyright (c) 1990 Jan-Simon Pendry
 * Copyright (c) 1990 Imperial College of Science, Technology & Medicine
 * Copyright (c) 1990 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Jan-Simon Pendry at Imperial College, London.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *      @(#)mtab_file.c 5.3 (Berkeley) 5/12/91
 *
 * $Id: mtab_file.c,v 5.2.1.3 91/05/07 22:19:58 jsp Alpha $
 *
 */

#include "am.h"

#ifdef READ_MTAB_FROM_FILE

#ifdef USE_FCNTL
#include <fcntl.h>
#else
#include <sys/file.h>
#endif /* USE_FCNTL */

#ifdef UPDATE_MTAB

/*
 * Do strict /etc/mtab locking
 */
#define MTAB_LOCKING

/*
 * Firewall mtab entries
 */
#define MTAB_STRIPNL

#include <sys/stat.h>
static FILE *mnt_file;

/*
 * If the system is being trashed by something, then
 * opening mtab may fail with ENFILE.  So, go to sleep
 * for a second and try again. (Yes - this has happened to me.)
 *
 * Note that this *may* block the automounter, oh well.
 * If we get to this state then things are badly wrong anyway...
 *
 * Give the system 10 seconds to recover but then give up.
 * Hopefully something else will exit and free up some file
 * table slots in that time.
 */
#define NFILE_RETRIES   10 /* seconds */

#ifdef MTAB_LOCKING
#ifdef LOCK_FCNTL
static int lock(fd)
{
        int rc;
        struct flock lk;

        lk.l_type = F_WRLCK;
        lk.l_whence = 0;
        lk.l_start = 0;
        lk.l_len = 0;

again:
        rc = fcntl(fd, F_SETLKW, (caddr_t) &lk);
        if (rc < 0 && (errno == EACCES || errno == EAGAIN)) {
#ifdef DEBUG
                dlog("Blocked, trying to obtain exclusive mtab lock");
#endif /* DEBUG */
                sleep(1);
                goto again;
        }
        return rc;
}
#else
#define lock(fd) (flock((fd), LOCK_EX))
#endif /* LOCK_FCNTL */
#endif /* MTAB_LOCKING */

static FILE *open_locked_mtab(mtab_file, mode, fs)
char *mtab_file;
char *mode;
char *fs;
{
        FILE *mfp = 0;

#ifdef UPDATE_MTAB
        /*
         * There is a possible race condition if two processes enter
         * this routine at the same time.  One will be blocked by the
         * exclusive lock below (or by the shared lock in setmntent)
         * and by the time the second process has the exclusive lock
         * it will be on the wrong underlying object.  To check for this
         * the mtab file is stat'ed before and after all the locking
         * sequence, and if it is a different file then we assume that
         * it may be the wrong file (only "may", since there is another
         * race between the initial stat and the setmntent).
         *
         * Simpler solutions to this problem are invited...
         */
        int racing = 2;
#ifdef MTAB_LOCKING
        int rc;
        int retries = 0;
        struct stat st_before, st_after;
#endif /* MTAB_LOCKING */

        if (mnt_file) {
#ifdef DEBUG
                dlog("Forced close on %s in read_mtab", mtab_file);
#endif /* DEBUG */
                endmntent(mnt_file);
                mnt_file = 0;
        }

#ifdef MTAB_LOCKING
again:
        if (mfp) {
                endmntent(mfp);
                mfp = 0;
        }

        clock_valid = 0;
        if (stat(mtab_file, &st_before) < 0) {
                plog(XLOG_ERROR, "%s: stat: %m", mtab_file);
                if (errno == ESTALE) {
                        /* happens occasionally */
                        sleep(1);
                        goto again;
                }
                return 0;
        }
#endif /* MTAB_LOCKING */
#endif /* UPDATE_MTAB */

eacces:
        mfp = setmntent(mtab_file, mode);
        if (!mfp) {
                /*
                 * Since setmntent locks the descriptor, it
                 * is possible it can fail... so retry if
                 * needed.
                 */
                if (errno == EACCES || errno == EAGAIN) {
#ifdef DEBUG
                        dlog("Blocked, trying to obtain exclusive mtab lock");
#endif /* DEBUG */
                        goto eacces;
                } else if (errno == ENFILE && retries++ < NFILE_RETRIES) {
                        sleep(1);
                        goto eacces;
                }

                plog(XLOG_ERROR, "setmntent(\"%s\", \"%s\"): %m", mtab_file, mode);
                return 0;
        }

#ifdef MTAB_LOCKING
#ifdef UPDATE_MTAB
        /*
         * At this point we have an exclusive lock on the mount list,
         * but it may be the wrong one so...
         */

        /*
         * Need to get an exclusive lock on the current
         * mount table until we have a new copy written
         * out, when the lock is released in free_mntlist.
         * flock is good enough since the mount table is
         * not shared between machines.
         */
        do
                rc = lock(fileno(mfp));
        while (rc < 0 && errno == EINTR);
        if (rc < 0) {
                plog(XLOG_ERROR, "Couldn't lock %s: %m", mtab_file);
                endmntent(mfp);
                return 0;
        }
        /*
         * Now check whether the mtab file has changed under our feet
         */
        if (stat(mtab_file, &st_after) < 0) {
                plog(XLOG_ERROR, "%s: stat", mtab_file);
                goto again;
        }

        if (st_before.st_dev != st_after.st_dev ||
                st_before.st_ino != st_after.st_ino) {
                        struct timeval tv;
                        if (racing == 0) {
                                /* Sometimes print a warning */
                                plog(XLOG_WARNING,
                                        "Possible mount table race - retrying %s", fs);
                        }
                        racing = (racing+1) & 3;
                        /*
                         * Take a nap.  From: Doug Kingston <dpk@morgan.com>
                         */
                        tv.tv_sec = 0;
                        tv.tv_usec = (mypid & 0x07) << 17;
                        if (tv.tv_usec)
                                if (select(0, (voidp) 0, (voidp) 0, (voidp) 0, &tv) < 0)
                                        plog(XLOG_WARNING, "mtab nap failed: %m");

                        goto again;
        }
#endif /* UPDATE_MTAB */
#endif /* MTAB_LOCKING */

        return mfp;
}

/*
 * Unlock the mount table
 */
void unlock_mntlist P((void));
void unlock_mntlist()
{
        /*
         * Release file lock, by closing the file
         */
        if (mnt_file) {
                endmntent(mnt_file);
                mnt_file = 0;
        }
}

/*
 * Write out a mount list
 */
void rewrite_mtab(mp)
mntlist *mp;
{
        FILE *mfp;

        /*
         * Concoct a temporary name in the same
         * directory as the target mount table
         * so that rename() will work.
         */
        char tmpname[64];
        int retries;
        int tmpfd;
        char *cp;
        char *mcp = mtab;
        cp = strrchr(mcp, '/');
        if (cp) {
                bcopy(mcp, tmpname, cp - mcp);
                tmpname[cp-mcp] = '\0';
        } else {
                plog(XLOG_WARNING, "No '/' in mtab (%s), using \".\" as tmp directory", mtab);
                tmpname[0] = '.'; tmpname[1] = '\0';
        }
        strcat(tmpname, "/mtabXXXXXX");
        mktemp(tmpname);
        retries = 0;
enfile1:
        if ((tmpfd = open(tmpname, O_RDWR|O_CREAT|O_TRUNC, 0644)) < 0) {
                if (errno == ENFILE && retries++ < NFILE_RETRIES) {
                        sleep(1);
                        goto enfile1;
                }
                plog(XLOG_ERROR, "%s: open: %m", tmpname);
                return;
        }
        if (close(tmpfd) < 0)
                plog(XLOG_ERROR, "Couldn't close tmp file descriptor: %m");

        retries = 0;
enfile2:
        mfp = setmntent(tmpname, "w");
        if (!mfp) {
                if (errno == ENFILE && retries++ < NFILE_RETRIES) {
                        sleep(1);
                        goto enfile2;
                }
                plog(XLOG_ERROR, "setmntent(\"%s\", \"w\"): %m", tmpname);
                return;
        }

        while (mp) {
                if (mp->mnt)
                        if (addmntent(mfp, mp->mnt))
                                plog(XLOG_ERROR, "Can't write entry to %s", tmpname);
                mp = mp->mnext;
        }

        endmntent(mfp);

        /*
         * Rename temporary mtab to real mtab
         */
        if (rename(tmpname, mtab) < 0)
                plog(XLOG_ERROR, "rename %s to %s: %m", tmpname, mtab);
}

#ifdef MTAB_STRIPNL
static void mtab_stripnl(s)
char *s;
{
        do {
                s = strchr(s, '\n');
                if (s)
                        *s++ = ' ';
        } while (s);
}
#endif /* MTAB_STRIPNL */

/*
 * Append a mntent structure to the
 * current mount table.
 */
void write_mntent(mp)
struct mntent *mp;
{
        int retries = 0;
        FILE *mfp;
enfile:
        mfp = open_locked_mtab(mtab, "a", mp->mnt_dir);
        if (mfp) {
#ifdef MTAB_STRIPNL
                mtab_stripnl(mp->mnt_opts);
#endif /* MTAB_STRIPNL */
                if (addmntent(mfp, mp))
                        plog(XLOG_ERROR, "Couldn't write %s: %m", mtab);
                endmntent(mfp);
        } else {
                if (errno == ENFILE && retries < NFILE_RETRIES) {
                        sleep(1);
                        goto enfile;
                }
                plog(XLOG_ERROR, "setmntent(\"%s\", \"a\"): %m", mtab);
        }
}

#endif /* UPDATE_MTAB */

static struct mntent *mnt_dup(mp)
struct mntent *mp;
{
        struct mntent *new_mp = ALLOC(mntent);

        new_mp->mnt_fsname = strdup(mp->mnt_fsname);
        new_mp->mnt_dir = strdup(mp->mnt_dir);
        new_mp->mnt_type = strdup(mp->mnt_type);
        new_mp->mnt_opts = strdup(mp->mnt_opts);

        new_mp->mnt_freq = mp->mnt_freq;
        new_mp->mnt_passno = mp->mnt_passno;

#ifdef FIXUP_MNTENT_DUP
        /*
         * Additional fields get dup'ed here
         */
        FIXUP_MNTENT_DUP(new_mp, mp);
#endif

        return new_mp;
}

/*
 * Read a mount table into memory
 */
mntlist *read_mtab(fs)
char *fs;
{
        mntlist **mpp, *mhp;

        struct mntent *mep;
        FILE *mfp = open_locked_mtab(mtab, "r+", fs);

        if (!mfp)
                return 0;

        mpp = &mhp;

/*
 * XXX - In SunOS 4 there is (yet another) memory leak
 * which loses 1K the first time getmntent is called.
 * (jsp)
 */
        while (mep = getmntent(mfp)) {
                /*
                 * Allocate a new slot
                 */
                *mpp = ALLOC(mntlist);

                /*
                 * Copy the data returned by getmntent
                 */
                (*mpp)->mnt = mnt_dup(mep);

                /*
                 * Move to next pointer
                 */
                mpp = &(*mpp)->mnext;
        }
        *mpp = 0;

#ifdef UPDATE_MTAB
        /*
         * If we are not updating the mount table then we
         * can free the resources held here, otherwise they
         * must be held until the mount table update is complete
         */
        mnt_file = mfp;
#else
        endmntent(mfp);
#endif /* UPDATE_MTAB */

        return mhp;
}

#endif /* READ_MTAB_FROM_FILE */