The command
# mount -oremount <spec> <dir>
doesn't read fstab or mtab. This is expected behaviour. Unfortunately,
we have to care about the internal loop= option which is generated and
maintained by mount(8)/umount(8). The loop= option has to be persistent.
How to reproduce this bug:
# mount -o loop /home/images/vfat.img /mnt/img; grep vfat /etc/mtab; \
mount -o remount,ro /home/images/vfat.img /mnt/img; grep vfat /etc/mtab;
/home/images/vfat.img /mnt/img vfat rw,loop=/dev/loop0 0 0
/home/images/vfat.img /mnt/img vfat ro 0 0
Reported-By: David Chinner <dgc@xxxxxxx>
Signed-off-by: Karel Zak <kzak@xxxxxxxxxx>
---
mount/fstab.c | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
mount/mount.8 | 21 ++++++++++++++
2 files changed, 104 insertions(+), 1 deletions(-)
diff --git a/mount/fstab.c b/mount/fstab.c
index 108010f..ae860da 100644
--- a/mount/fstab.c
+++ b/mount/fstab.c
@@ -669,6 +669,86 @@ lock_mtab (void) {
}
}
+static char *
+get_option(const char *optname, const char *src, size_t *len)
+{
+ char *opt, *end;
+ size_t sz;
+
+ if (!src)
+ return NULL;
+
+ opt = strstr(src, optname);
+ if (!opt)
+ return NULL;
+
+ end = strchr(opt, ',');
+ sz = end ? end - opt : strlen(opt);
+
+ if (len)
+ *len = sz;
+
+ if ((opt == src || *(opt - 1) == ',') &&
+ (*(opt + sz) == '\0' || *(opt + sz) == ','))
+ return opt;
+
+ return NULL;
+}
+
+static int
+cpy_option(const char *optname, char *dest, const char *src)
+{
+ char *opt;
+ size_t sz;
+
+ opt = get_option(optname, src, &sz);
+ if (!opt)
+ /* the option doesn't exist */
+ return 0;
+
+ if (get_option(optname, dest, NULL))
+ /* the options is already in dest */
+ return 0;
+
+ if (*dest) {
+ dest = dest + strlen(dest);
+ *dest++ = ','; /* separator */
+ }
+ memcpy(dest, opt, sz); /* copy option */
+ *(dest + sz) = '\0'; /* terminator */
+
+ return 1;
+}
+
+/* Generates (and allocates) new options for remount
+ *
+ * We cannot blindly replace the old options, otherwise we will lost some
+ * internally generated stuff (e.g loop=).
+ */
+static char *
+mk_remount_opts(const char *old, const char *instead)
+{
+ char *new;
+ size_t sz;
+
+ if (old == NULL && instead == NULL)
+ return NULL;
+ if (!old)
+ return xstrdup(instead);
+
+ /* max size of new options is:
+ * old + new + '\0' + separator (for each copied option)
+ */
+ sz = strlen(old) + (instead ? strlen(instead) : 0) + 2;
+ new = xmalloc(sz);
+ if (instead)
+ strncpy(new, instead, sz);
+
+ cpy_option("loop=", new, old);
+
+ return new;
+}
+
/*
* Update the mtab.
* Used by umount with null INSTEAD: remove the last DIR entry.
@@ -721,8 +801,10 @@ update_mtab (const char *dir, struct my_mntent *instead) {
}
} else if (!strcmp(mc->m.mnt_dir, instead->mnt_dir)) {
/* A remount */
+ char *opts = mk_remount_opts(mc->m.mnt_opts,
+ instead->mnt_opts);
my_free(mc->m.mnt_opts);
- mc->m.mnt_opts = xstrdup(instead->mnt_opts);
+ mc->m.mnt_opts = opts;
} else {
/* A move */
my_free(mc->m.mnt_dir);
diff --git a/mount/mount.8 b/mount/mount.8
index bb6b3f1..42d3e55 100644
--- a/mount/mount.8
+++ b/mount/mount.8
@@ -679,6 +679,27 @@ This option implies the options
Attempt to remount an already-mounted file system. This is commonly
used to change the mount flags for a file system, especially to make a
readonly file system writeable. It does not change device or mount point.
+
+The remount functionality follows the standard way how the mount command works
+with options from fstab. It means the mount command doesn't read fstab (or
+mtab) only when a
+.IR device
+and
+.IR dir
+are fully specified.
+
+.BR "mount -o remount,rw /dev/foo /dir"
+
+After this call all old mount options are replaced and arbitrary stuff from
+fstab is ignored, except the loop= option which is internally generated and
+maintained by the mount command.
+
+.BR "mount -o remount,rw /dir"
+
+After this call mount reads fstab (or mtab) and merges these options with
+options from command line (
+.B -o
+).
.TP
.B ro
Mount the file system read-only.
--
1.5.4.1
--
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