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mtab.c
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#include "util.h"
extern char *prog_name;
extern char *fsname;
extern int verbose;
static int ignoring_mtab;
/* Don't bother with /etc/mtab if:
- /etc/mtab is a link to /proc/mounts
- there is no /etc/mtab file
- we can't write to /etc/mtab */
static int ignore_mtab(void)
{
struct stat sbuf;
int fd;
if (ignoring_mtab)
return 1;
if (lstat("/etc/mtab", &sbuf) < 0)
goto do_ignore;
if (S_ISLNK(sbuf.st_mode))
goto do_ignore;
fd = open("/etc/mtab", O_RDWR, 0644);
if (fd < 0)
goto do_ignore;
close(fd);
return 0;
do_ignore:
ignoring_mtab = 1;
return 1;
}
/* Whichever process successfully links their own /etc/mtab~pid file to
/etc/mtab~ gets the lock. We just sleep/retry until we get the lock.
This is the locking method used by util-linux/mount/fstab.c which we
need to keep in sync with. */
static void lock_mtab(void)
{
char fname[32];
int rv, fd, e, retries = 0;
if (ignore_mtab())
return;
sprintf(fname, "/etc/mtab~%d", getpid());
retry:
fd = open(fname, O_WRONLY|O_CREAT, 0);
e = errno;
if (fd < 0)
die("can't create mtab lock file %s: %s\n", fname, strerror(e));
close(fd);
rv = link(fname, "/etc/mtab~");
e = errno;
unlink(fname);
if (rv < 0 && e != EEXIST)
die("can't link %s to /etc/mtab~: %s\n", fname, strerror(e));
if (rv < 0) {
if (++retries > 5)
warn("waiting to lock /etc/mtab~: try unlinking "
"stale /etc/mtab~ file\n");
sleep(1);
goto retry;
}
}
static void unlock_mtab(void)
{
if (ignore_mtab())
return;
unlink("/etc/mtab~");
}
void add_mtab_entry(struct mount_options *mo)
{
FILE *file;
read_proc_mounts(mo);
if (ignore_mtab())
return;
lock_mtab();
file = fopen("/etc/mtab", "a");
if (!file) {
warn("can't add entry to /etc/mtab");
return;
}
fprintf(file, "%s", mo->proc_entry);
fclose(file);
unlock_mtab();
}
/* This follows what util-linux/mount/fstab.c does wrt writing new mtab.tmp
and replacing /etc/mtab with it, we need to keep in sync with fstab.c's
procedure for this. */
void del_mtab_entry(struct mount_options *mo)
{
char line[PATH_MAX];
char device[PATH_MAX];
char path[PATH_MAX];
char type[16];
FILE *mtab, *mtmp;
mode_t old_umask;
struct stat sbuf;
int found = 0;
if (ignore_mtab())
return;
lock_mtab();
old_umask = umask(077);
mtmp = fopen("/etc/mtab.tmp", "w");
mtab = fopen("/etc/mtab", "r");
umask(old_umask);
if (!mtmp || !mtab)
goto fail;
while (fgets(line, PATH_MAX, mtab)) {
/* exclude the line matching the fs being unmounted
from the next version of mtab */
if ((sscanf(line, "%s %s %s", device, path, type) == 3) &&
(strncmp(type, "gfs", 3) == 0) &&
(strcmp(path, mo->dir) == 0) &&
(strcmp(device, mo->dev) == 0)) {
found = 1;
continue;
}
/* all other lines from mtab are included in
the next version of mtab */
if (fprintf(mtmp, "%s", line) < 0) {
int e = errno;
warn("error writing to /etc/mtab.tmp: %s", strerror(e));
}
}
if (!found) {
warn("file system mounted on %s not found in mtab", mo->dir);
goto fail;
}
if (fchmod(fileno(mtmp), S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH) < 0) {
int e = errno;
warn("error changing mode of /etc/mtab.tmp: %s", strerror(e));
}
if (stat("/etc/mtab", &sbuf) < 0) {
int e = errno;
warn("error stating /etc/mtab: %s", strerror(e));
} else
if(chown("/etc/mtab.tmp", sbuf.st_uid, sbuf.st_gid) < 0) {
int e = errno;
warn("error changing owner of /etc/mtab.tmp: %s", strerror(e));
}
fclose(mtmp);
fclose(mtab);
if (rename("/etc/mtab.tmp", "/etc/mtab") < 0) {
int e = errno;
warn("can't rename /etc/mtab.tmp to /etc/mtab: %s",
strerror(e));
goto fail_unlink;
}
unlock_mtab();
return;
fail:
fclose(mtmp);
fclose(mtab);
fail_unlink:
unlink("/etc/mtab.tmp");
unlock_mtab();
}

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