[PATCH] introduce slave mounts

A slave mount always has a master mount from which it receives
mount/umount events.  Unlike shared mount the event propagation does not
flow from the slave mount to the master.

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 51 insertions, 3 deletions

diff --git a/fs/pnode.c b/fs/pnode.c
index 7bc942d047cd..f73eba24f1d1 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -17,13 +17,61 @@ static inline struct vfsmount *next_peer(struct vfsmount *p)
         return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
 }
 
+static int do_make_slave(struct vfsmount *mnt)
+{
+        struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
+        struct vfsmount *slave_mnt;
+
+        /*
+         * slave 'mnt' to a peer mount that has the
+         * same root dentry. If none is available than
+         * slave it to anything that is available.
+         */
+        while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
+               peer_mnt->mnt_root != mnt->mnt_root) ;
+
+        if (peer_mnt == mnt) {
+                peer_mnt = next_peer(mnt);
+                if (peer_mnt == mnt)
+                        peer_mnt = NULL;
+        }
+        list_del_init(&mnt->mnt_share);
+
+        if (peer_mnt)
+                master = peer_mnt;
+
+        if (master) {
+                list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
+                        slave_mnt->mnt_master = master;
+                list_del(&mnt->mnt_slave);
+                list_add(&mnt->mnt_slave, &master->mnt_slave_list);
+                list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
+                INIT_LIST_HEAD(&mnt->mnt_slave_list);
+        } else {
+                struct list_head *p = &mnt->mnt_slave_list;
+                while (!list_empty(p)) {
+                        slave_mnt = list_entry(p->next,
+                                        struct vfsmount, mnt_slave);
+                        list_del_init(&slave_mnt->mnt_slave);
+                        slave_mnt->mnt_master = NULL;
+                }
+        }
+        mnt->mnt_master = master;
+        CLEAR_MNT_SHARED(mnt);
+        INIT_LIST_HEAD(&mnt->mnt_slave_list);
+        return 0;
+}
+
 void change_mnt_propagation(struct vfsmount *mnt, int type)
 {
         if (type == MS_SHARED) {
                 set_mnt_shared(mnt);
-        } else {
-                list_del_init(&mnt->mnt_share);
-                mnt->mnt_flags &= ~MNT_PNODE_MASK;
+                return;
+        }
+        do_make_slave(mnt);
+        if (type != MS_SLAVE) {
+                list_del_init(&mnt->mnt_slave);
+                mnt->mnt_master = NULL;
         }
 }