Add .zfs control directory

Add support for the .zfs control directory.  This was accomplished
by leveraging as much of the existing ZFS infrastructure as posible
and updating it for Linux as required.  The bulk of the core
functionality is now all there with the following limitations.

*) The .zfs/snapshot directory automount support requires a 2.6.37
   or newer kernel.  The exception is RHEL6.2 which has backported
   the d_automount patches.

*) Creating/destroying/renaming snapshots with mkdir/rmdir/mv
   in the .zfs/snapshot directory works as expected.  However,
   this functionality is only available to root until zfs
   delegations are finished.

      * mkdir - create a snapshot
      * rmdir - destroy a snapshot
      * mv    - rename a snapshot

The following issues are known defeciences, but we expect them to
be addressed by future commits.

*) Add automount support for kernels older the 2.6.37.  This should
   be possible using follow_link() which is what Linux did before.

*) Accessing the .zfs/snapshot directory via NFS is not yet possible.
   The majority of the ground work for this is complete.  However,
   finishing this work will require resolving some lingering
   integration issues with the Linux NFS kernel server.

*) The .zfs/shares directory exists but no futher smb functionality
   has yet been implemented.

Contributions-by: Rohan Puri <[email protected]>
Contributiobs-by: Andrew Barnes <[email protected]>
Signed-off-by: Brian Behlendorf <[email protected]>
Closes #173

1 files changed, 17 insertions, 7 deletions

diff --git a/module/zfs/zpl_super.c b/module/zfs/zpl_super.c
index 0e6e9360f..98d0a0312 100644
--- a/module/zfs/zpl_super.c
+++ b/module/zfs/zpl_super.c
@@ -26,6 +26,7 @@
 #include <sys/zfs_vfsops.h>
 #include <sys/zfs_vnops.h>
 #include <sys/zfs_znode.h>
+#include <sys/zfs_ctldir.h>
 #include <sys/zpl.h>
 
 
@@ -139,6 +140,20 @@ zpl_remount_fs(struct super_block *sb, int *flags, char *data)
 	return (error);
 }
 
+static void
+zpl_umount_begin(struct super_block *sb)
+{
+	zfs_sb_t *zsb = sb->s_fs_info;
+	int count;
+
+	/*
+	 * Best effort to unmount snapshots in .zfs/snapshot/.  Normally this
+	 * isn't required because snapshots have the MNT_SHRINKABLE flag set.
+	 */
+	if (zsb->z_ctldir)
+		(void) zfsctl_unmount_snapshots(zsb, MNT_FORCE, &count);
+}
+
 /*
  * The Linux VFS automatically handles the following flags:
  * MNT_NOSUID, MNT_NODEV, MNT_NOEXEC, MNT_NOATIME, MNT_READONLY
@@ -199,13 +214,7 @@ zpl_get_sb(struct file_system_type *fs_type, int flags,
 static void
 zpl_kill_sb(struct super_block *sb)
 {
-#ifdef HAVE_SNAPSHOT
-	zfs_sb_t *zsb = sb->s_fs_info;
-
-	if (zsb && dmu_objset_is_snapshot(zsb->z_os))
-		zfs_snap_destroy(zsb);
-#endif /* HAVE_SNAPSHOT */
-
+	zfs_preumount(sb);
 	kill_anon_super(sb);
 }
 
@@ -306,6 +315,7 @@ const struct super_operations zpl_super_operations = {
 	.sync_fs		= zpl_sync_fs,
 	.statfs			= zpl_statfs,
 	.remount_fs		= zpl_remount_fs,
+	.umount_begin		= zpl_umount_begin,
 	.show_options		= zpl_show_options,
 	.show_stats		= NULL,
 #ifdef HAVE_NR_CACHED_OBJECTS