[PATCH] jail mount/unmount patch

Please review my attached patch.

The patch fixes f_mntonname with mount/unmount inside a jail with allow.mount enabled.
Filesystems mountable in a jail require the VFCF_JAIL flag (currently only ZFS).

With this patch, mount and unmount works both with enforce_statfs = 0 and enforce_statfs = 1.
I suggest disabling mount/unmount for jails with enforce_statfs = 2, as this is contradictory and does not play well with or without this patch.

I have successfully tested this patch with ZFS, nullfs and tmpfs.

To enable nullfs for a jail, you have to modify tmpfs/tmpfs_vfsops.c and recompile the tmpfs module:
-VFS_SET(tmpfs_vfsops, tmpfs, 0);
+VFS_SET(tmpfs_vfsops, tmpfs, VFCF_JAIL);

To enable tmpfs for a jail, you have to modify nullfs/null_vfsops.c and recompile the nullfs module:
-VFS_SET(null_vfsops, nullfs, VFCF_LOOPBACK);
+VFS_SET(null_vfsops, nullfs, VFCF_LOOPBACK | VFCF_JAIL);

The filesystems can be successfully mounted/unmounted inside a jail and also unmounted from the parent host without problems.

The mount inside jail, a jail needs allow.mount=1 and enforce.statfs=0 or enforce.statfs=1, for more information see jail(8)
I assume other filesystem not dealing with devices may work correctly with this patch, too (e.g. nfs).

With jailed nullfs we can run tinderbox in a jail ;)

Please review, comment and/or test my attached patch.

Cheers,
mm

-- 
Martin Matuska
FreeBSD committer
http://blog.vx.sk