[PATCH] handling of slave mounts

This makes bind, rbind, move, clone namespace and umount operations
aware of the semantics of slave mount (see Documentation/sharedsubtree.txt
in the last patch of the series for detailed description).

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, 72 insertions, 9 deletions

diff --git a/fs/pnode.c b/fs/pnode.c
index f73eba24f1d1..3e266c5a3071 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -17,6 +17,16 @@ static inline struct vfsmount *next_peer(struct vfsmount *p)
         return list_entry(p->mnt_share.next, struct vfsmount, mnt_share);
 }
 
+static inline struct vfsmount *first_slave(struct vfsmount *p)
+{
+        return list_entry(p->mnt_slave_list.next, struct vfsmount, mnt_slave);
+}
+
+static inline struct vfsmount *next_slave(struct vfsmount *p)
+{
+        return list_entry(p->mnt_slave.next, struct vfsmount, mnt_slave);
+}
+
 static int do_make_slave(struct vfsmount *mnt)
 {
         struct vfsmount *peer_mnt = mnt, *master = mnt->mnt_master;
@@ -83,10 +93,64 @@ void change_mnt_propagation(struct vfsmount *mnt, int type)
 static struct vfsmount *propagation_next(struct vfsmount *m,
                                          struct vfsmount *origin)
 {
-        m = next_peer(m);
-        if (m == origin)
-                return NULL;
-        return m;
+        /* are there any slaves of this mount? */
+        if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
+                return first_slave(m);
+
+        while (1) {
+                struct vfsmount *next;
+                struct vfsmount *master = m->mnt_master;
+
+                if ( master == origin->mnt_master ) {
+                        next = next_peer(m);
+                        return ((next == origin) ? NULL : next);
+                } else if (m->mnt_slave.next != &master->mnt_slave_list)
+                        return next_slave(m);
+
+                /* back at master */
+                m = master;
+        }
+}
+
+/*
+ * return the source mount to be used for cloning
+ *
+ * @dest        the current destination mount
+ * @last_dest   the last seen destination mount
+ * @last_src    the last seen source mount
+ * @type        return CL_SLAVE if the new mount has to be
+ *              cloned as a slave.
+ */
+static struct vfsmount *get_source(struct vfsmount *dest,
+                                        struct vfsmount *last_dest,
+                                        struct vfsmount *last_src,
+                                        int *type)
+{
+        struct vfsmount *p_last_src = NULL;
+        struct vfsmount *p_last_dest = NULL;
+        *type = CL_PROPAGATION;;
+
+        if (IS_MNT_SHARED(dest))
+                *type |= CL_MAKE_SHARED;
+
+        while (last_dest != dest->mnt_master) {
+                p_last_dest = last_dest;
+                p_last_src = last_src;
+                last_dest = last_dest->mnt_master;
+                last_src = last_src->mnt_master;
+        }
+
+        if (p_last_dest) {
+                do {
+                        p_last_dest = next_peer(p_last_dest);
+                } while (IS_MNT_NEW(p_last_dest));
+        }
+
+        if (dest != p_last_dest) {
+                *type |= CL_SLAVE;
+                return last_src;
+        } else
+                return p_last_src;
 }
 
 /*
@@ -114,16 +178,15 @@ int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
 
         for (m = propagation_next(dest_mnt, dest_mnt); m;
                         m = propagation_next(m, dest_mnt)) {
-                int type = CL_PROPAGATION;
+                int type;
+                struct vfsmount *source;
 
                 if (IS_MNT_NEW(m))
                         continue;
 
-                if (IS_MNT_SHARED(m))
-                        type |= CL_MAKE_SHARED;
+                source =  get_source(m, prev_dest_mnt, prev_src_mnt, &type);
 
-                if (!(child = copy_tree(source_mnt, source_mnt->mnt_root,
-                                                type))) {
+                if (!(child = copy_tree(source, source->mnt_root, type))) {
                         ret = -ENOMEM;
                         list_splice(tree_list, tmp_list.prev);
                         goto out;