[lxc-devel] Fixed (hacked) LXC to apply mount options for bind mounts

[Ciprian Dorin, Craciun]

    Hello all!

    This bug stalked me for a while, but only now it bit me quite
badly... (Lost about an hour of work...)

    So the culprit: inside the fstab file for the `lxc.mount` option I
can use options like `ro` together with `bind`. Unfortunately the
kernel just laughs in my face and ignores any options I've put in
there... :) But not any more: I've updated `./src/lxc/conf.c`
(`mount_file_entries` function) so that when it encounters a `bind`
option it executes it twice (one without any extra options, and a
second time with the remount flag set.)

    I've marginally (as in my particular case) tested it and it works.

    Any other ideas on how to solve this? Any comments?
    Ciprian.

    P.S.: One question though (both in the patched and unpatched
versions): it seems that if I put two lines inside the fstab, once
with only `bind` options, and a second one with `remount,ro` option it
doesn't work and I receive the error `No such device - failed to
mount`. But this is equivalent with what my patched version is doing
(which works)... Strange...


diff --git a/src/lxc/conf.c b/src/lxc/conf.c
index 26ddd03..f7c5816 100644
--- a/src/lxc/conf.c
+++ b/src/lxc/conf.c
@@ -801,11 +801,20 @@ static int mount_file_entries(FILE *file)
                }

                if (mount(mntent->mnt_fsname, mntent->mnt_dir,
-                         mntent->mnt_type, mntflags, mntdata)) {
+                         mntent->mnt_type, mntflags & ~MS_REMOUNT, mntdata)) {
                        SYSERROR("failed to mount '%s' on '%s'",
                                         mntent->mnt_fsname, mntent->mnt_dir);
                        goto out;
                }
+               if ((mntflags & MS_REMOUNT == MS_REMOUNT) || (mntflags
& MS_BIND == MS_BIND)) {
+                       DEBUG ("remounting %s on %s to respect bind or
remount options", mntent->mnt_fsname, mntent->mnt_dir);
+                       if (mount(mntent->mnt_fsname, mntent->mnt_dir,
+                                 mntent->mnt_type, mntflags |
MS_REMOUNT, mntdata)) {
+                               SYSERROR("failed to mount '%s' on '%s'",
+                                                mntent->mnt_fsname,
mntent->mnt_dir);
+                               goto out;
+                       }
+               }

                DEBUG("mounted %s on %s, type %s", mntent->mnt_fsname,
                      mntent->mnt_dir, mntent->mnt_type);