From 19fcec84d8d7d21e796c7624e521b60d28ee21ed Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:45:59 +0200 Subject: Adding upstream version 16.2.11+ds. Signed-off-by: Daniel Baumann --- src/mount/mtab.c | 294 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 294 insertions(+) create mode 100644 src/mount/mtab.c (limited to 'src/mount/mtab.c') diff --git a/src/mount/mtab.c b/src/mount/mtab.c new file mode 100644 index 000000000..3ce368fd3 --- /dev/null +++ b/src/mount/mtab.c @@ -0,0 +1,294 @@ + +/* + * this code lifted from util-linux-ng, licensed GPLv2+, + * + * git://git.kernel.org/pub/scm/utils/util-linux-ng/util-linux-ng.git + * + * whoever decided that each special mount program is responsible + * for updating /etc/mtab should be spanked. + * + * + */ +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "mount/canonicalize.c" + + +/* Updating mtab ----------------------------------------------*/ + +/* Flag for already existing lock file. */ +static int we_created_lockfile = 0; +static int lockfile_fd = -1; + +/* Flag to indicate that signals have been set up. */ +static int signals_have_been_setup = 0; + +/* Ensure that the lock is released if we are interrupted. */ +extern char *strsignal(int sig); /* not always in */ + +static void +setlkw_timeout (int sig) { + /* nothing, fcntl will fail anyway */ +} + +#define _PATH_MOUNTED "/etc/mtab" +#define _PATH_MOUNTED_LOCK "/etc/mtab~" +#define PROC_SUPER_MAGIC 0x9fa0 + +/* exit status - bits below are ORed */ +#define EX_USAGE 1 /* incorrect invocation or permission */ +#define EX_SYSERR 2 /* out of memory, cannot fork, ... */ +#define EX_SOFTWARE 4 /* internal mount bug or wrong version */ +#define EX_USER 8 /* user interrupt */ +#define EX_FILEIO 16 /* problems writing, locking, ... mtab/fstab */ +#define EX_FAIL 32 /* mount failure */ +#define EX_SOMEOK 64 /* some mount succeeded */ + +int die(int err, const char *fmt, ...) { + va_list args; + + va_start(args, fmt); + vfprintf(stderr, fmt, args); + fprintf(stderr, "\n"); + va_end(args); + + exit(err); +} + +static void +handler (int sig) { + die(EX_USER, "%s", strsignal(sig)); +} + +/* Remove lock file. */ +void +unlock_mtab (void) { + if (we_created_lockfile) { + close(lockfile_fd); + lockfile_fd = -1; + unlink (_PATH_MOUNTED_LOCK); + we_created_lockfile = 0; + } +} + +/* Create the lock file. + The lock file will be removed if we catch a signal or when we exit. */ +/* The old code here used flock on a lock file /etc/mtab~ and deleted + this lock file afterwards. However, as rgooch remarks, that has a + race: a second mount may be waiting on the lock and proceed as + soon as the lock file is deleted by the first mount, and immediately + afterwards a third mount comes, creates a new /etc/mtab~, applies + flock to that, and also proceeds, so that the second and third mount + now both are scribbling in /etc/mtab. + The new code uses a link() instead of a creat(), where we proceed + only if it was us that created the lock, and hence we always have + to delete the lock afterwards. Now the use of flock() is in principle + superfluous, but avoids an arbitrary sleep(). */ + +/* Where does the link point to? Obvious choices are mtab and mtab~~. + HJLu points out that the latter leads to races. Right now we use + mtab~. instead. Use 20 as upper bound for the length of %d. */ +#define MOUNTLOCK_LINKTARGET _PATH_MOUNTED_LOCK "%d" +#define MOUNTLOCK_LINKTARGET_LTH (sizeof(_PATH_MOUNTED_LOCK)+20) + +/* + * The original mount locking code has used sleep(1) between attempts and + * maximal number of attempts has been 5. + * + * There was very small number of attempts and extremely long waiting (1s) + * that is useless on machines with large number of concurret mount processes. + * + * Now we wait few thousand microseconds between attempts and we have global + * time limit (30s) rather than limit for number of attempts. The advantage + * is that this method also counts time which we spend in fcntl(F_SETLKW) and + * number of attempts is not so much restricted. + * + * -- kzak@redhat.com [2007-Mar-2007] + */ + +/* maximum seconds between first and last attempt */ +#define MOUNTLOCK_MAXTIME 30 + +/* sleep time (in microseconds, max=999999) between attempts */ +#define MOUNTLOCK_WAITTIME 5000 + +void +lock_mtab (void) { + int i; + struct timespec waittime; + struct timeval maxtime; + char linktargetfile[MOUNTLOCK_LINKTARGET_LTH]; + + if (!signals_have_been_setup) { + int sig = 0; + struct sigaction sa; + + sa.sa_handler = handler; + sa.sa_flags = 0; + sigfillset (&sa.sa_mask); + + while (sigismember (&sa.sa_mask, ++sig) != -1 + && sig != SIGCHLD) { + if (sig == SIGALRM) + sa.sa_handler = setlkw_timeout; + else + sa.sa_handler = handler; + sigaction (sig, &sa, (struct sigaction *) 0); + } + signals_have_been_setup = 1; + } + + snprintf(linktargetfile, sizeof(linktargetfile), MOUNTLOCK_LINKTARGET, + getpid ()); + + i = open (linktargetfile, O_WRONLY|O_CREAT, S_IRUSR|S_IWUSR); + if (i < 0) { + int errsv = errno; + /* linktargetfile does not exist (as a file) + and we cannot create it. Read-only filesystem? + Too many files open in the system? + Filesystem full? */ + die (EX_FILEIO, "can't create lock file %s: %s " + "(use -n flag to override)", + linktargetfile, strerror (errsv)); + } + close(i); + + gettimeofday(&maxtime, NULL); + maxtime.tv_sec += MOUNTLOCK_MAXTIME; + + waittime.tv_sec = 0; + waittime.tv_nsec = (1000 * MOUNTLOCK_WAITTIME); + + /* Repeat until it was us who made the link */ + while (!we_created_lockfile) { + struct timeval now; + struct flock flock; + int errsv, j; + + j = link(linktargetfile, _PATH_MOUNTED_LOCK); + errsv = errno; + + if (j == 0) + we_created_lockfile = 1; + + if (j < 0 && errsv != EEXIST) { + (void) unlink(linktargetfile); + die (EX_FILEIO, "can't link lock file %s: %s " + "(use -n flag to override)", + _PATH_MOUNTED_LOCK, strerror (errsv)); + } + + lockfile_fd = open (_PATH_MOUNTED_LOCK, O_WRONLY); + + if (lockfile_fd < 0) { + /* Strange... Maybe the file was just deleted? */ + int errsv = errno; + gettimeofday(&now, NULL); + if (errno == ENOENT && now.tv_sec < maxtime.tv_sec) { + we_created_lockfile = 0; + continue; + } + (void) unlink(linktargetfile); + die (EX_FILEIO, "can't open lock file %s: %s " + "(use -n flag to override)", + _PATH_MOUNTED_LOCK, strerror (errsv)); + } + + flock.l_type = F_WRLCK; + flock.l_whence = SEEK_SET; + flock.l_start = 0; + flock.l_len = 0; + + if (j == 0) { + /* We made the link. Now claim the lock. */ + if (fcntl (lockfile_fd, F_SETLK, &flock) == -1) { + /* proceed, since it was us who created the lockfile anyway */ + } + (void) unlink(linktargetfile); + } else { + /* Someone else made the link. Wait. */ + gettimeofday(&now, NULL); + if (now.tv_sec < maxtime.tv_sec) { + alarm(maxtime.tv_sec - now.tv_sec); + if (fcntl (lockfile_fd, F_SETLKW, &flock) == -1) { + int errsv = errno; + (void) unlink(linktargetfile); + die (EX_FILEIO, "can't lock lock file %s: %s", + _PATH_MOUNTED_LOCK, (errno == EINTR) ? + "timed out" : strerror (errsv)); + } + alarm(0); + + nanosleep(&waittime, NULL); + } else { + (void) unlink(linktargetfile); + die (EX_FILEIO, "Cannot create link %s\n" + "Perhaps there is a stale lock file?\n", + _PATH_MOUNTED_LOCK); + } + close(lockfile_fd); + } + } +} + +static void +update_mtab_entry(const char *spec, const char *node, const char *type, + const char *opts, int flags, int freq, int pass) { + struct statfs buf; + int err = statfs(_PATH_MOUNTED, &buf); + if (err) { + printf("mount: can't statfs %s: %s", _PATH_MOUNTED, + strerror (err)); + return; + } + /* /etc/mtab is symbol link to /proc/self/mounts? */ + if (buf.f_type == PROC_SUPER_MAGIC) + return; + + if (!opts) + opts = "rw"; + + struct mntent mnt; + mnt.mnt_fsname = strdup(spec); + mnt.mnt_dir = canonicalize_path(node); + mnt.mnt_type = strdup(type); + mnt.mnt_opts = strdup(opts); + mnt.mnt_freq = freq; + mnt.mnt_passno = pass; + + FILE *fp; + + lock_mtab(); + fp = setmntent(_PATH_MOUNTED, "a+"); + if (fp == NULL) { + int errsv = errno; + printf("mount: can't open %s: %s", _PATH_MOUNTED, + strerror (errsv)); + } else { + if ((addmntent (fp, &mnt)) == 1) { + int errsv = errno; + printf("mount: error writing %s: %s", + _PATH_MOUNTED, strerror (errsv)); + } + } + endmntent(fp); + unlock_mtab(); + + free(mnt.mnt_fsname); + free(mnt.mnt_dir); + free(mnt.mnt_type); + free(mnt.mnt_opts); +} -- cgit v1.2.3