[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>

diff --git a/fs/namespace.c b/fs/namespace.c
index 46f99bc..0896703 100644 (file)
--- 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 f73eba2..3e266c5 100644 (file)
--- 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;