mount: remount doesn't care about loop=

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@sgi.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 21 insertions, 0 deletions

diff --git a/mount/mount.8 b/mount/mount.8
index bb6b3f10b..42d3e55e3 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.