[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>

2 files changed, 121 insertions, 37 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 46f99bc585bd..089670363704 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -227,8 +227,17 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
                 mnt->mnt_mountpoint = mnt->mnt_root;
                 mnt->mnt_parent = mnt;
 
-                if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
-                        list_add(&mnt->mnt_share, &old->mnt_share);
+                if (flag & CL_SLAVE) {
+                        list_add(&mnt->mnt_slave, &old->mnt_slave_list);
+                        mnt->mnt_master = old;
+                        CLEAR_MNT_SHARED(mnt);
+                } else {
+                        if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
+                                list_add(&mnt->mnt_share, &old->mnt_share);
+                        if (IS_MNT_SLAVE(old))
+                                list_add(&mnt->mnt_slave, &old->mnt_slave);
+                        mnt->mnt_master = old->mnt_master;
+                }
                 if (flag & CL_MAKE_SHARED)
                         set_mnt_shared(mnt);
 
@@ -689,18 +698,18 @@ Enomem:
  *
  *  NOTE: in the table below explains the semantics when a source mount
  *  of a given type is attached to a destination mount of a given type.
- *      ---------------------------------------------
- *      |         BIND MOUNT OPERATION              |
- *      |********************************************
- *      | source-->| shared        |       private  |
- *      | dest     |               |                |
- *      |   |      |               |                |
- *      |   v      |               |                |
- *      |********************************************
- *      |  shared  | shared (++)   |     shared (+) |
- *      |          |               |                |
- *      |non-shared| shared (+)    |      private   |
- *      *********************************************
+ *      -------------------------------------------------------------
+ *      |         BIND MOUNT OPERATION                               |
+ *      |*************************************************************
+ *      | source-->| shared        |       private  |       slave    |
+ *      | dest     |               |                |                |
+ *      |   |      |               |                |                |
+ *      |   v      |               |                |                |
+ *      |*************************************************************
+ *      |  shared  | shared (++)   |     shared (+) |     shared(+++)|
+ *      |          |               |                |                |
+ *      |non-shared| shared (+)    |      private   |      slave (*) |
+ *      **************************************************************
  * A bind operation clones the source mount and mounts the clone on the
  * destination mount.
  *
@@ -710,21 +719,33 @@ Enomem:
  * (+)   the cloned mount is created under the destination mount and is marked
  *       as shared. The cloned mount is added to the peer group of the source
  *       mount.
- *      ---------------------------------------------
- *      |               MOVE MOUNT OPERATION        |
- *      |********************************************
- *      | source-->| shared        |       private  |
- *      | dest     |               |                |
- *      |   |      |               |                |
- *      |   v      |               |                |
- *      |********************************************
- *      |  shared  | shared (+)    |     shared (+) |
- *      |          |               |                |
- *      |non-shared| shared (+*)   |      private   |
- *      *********************************************
- * (+)  the mount is moved to the destination. And is then propagated to all
- *      the mounts in the propagation tree of the destination mount.
+ * (+++) the mount is propagated to all the mounts in the propagation tree
+ *       of the destination mount and the cloned mount is made slave
+ *       of the same master as that of the source mount. The cloned mount
+ *       is marked as 'shared and slave'.
+ * (*)   the cloned mount is made a slave of the same master as that of the
+ *       source mount.
+ *
+ *      --------------------------------------------------------------
+ *      |                       MOVE MOUNT OPERATION                 |
+ *      |*************************************************************
+ *      | source-->| shared        |       private  |       slave    |
+ *      | dest     |               |                |                |
+ *      |   |      |               |                |                |
+ *      |   v      |               |                |                |
+ *      |*************************************************************
+ *      |  shared  | shared (+)    |     shared (+) |    shared(+++) |
+ *      |          |               |                |                |
+ *      |non-shared| shared (+*)   |      private   |    slave (*)   |
+ *      **************************************************************
+ *
+ * (+)  the mount is moved to the destination. And is then propagated to
+ *      all the mounts in the propagation tree of the destination mount.
  * (+*)  the mount is moved to the destination.
+ * (+++)  the mount is moved to the destination and is then propagated to
+ *      all the mounts belonging to the destination mount's propagation tree.
+ *      the mount is marked as 'shared and slave'.
+ * (*)  the mount continues to be a slave at the new location.
  *
  * if the source mount is a tree, the operations explained above is
  * applied to each mount in the tree.
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;