[PATCH] shared mounts handling: move

Implement handling of mount --move in presense of shared mounts (see
Documentation/sharedsubtree.txt in the end of patch 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, 46 insertions, 17 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 9f5a084b239f..1487982dbc24 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -660,7 +660,10 @@ Enomem:
 
 /*
  *  @source_mnt : mount tree to be attached
- *  @nd        : place the mount tree @source_mnt is attached
+ *  @nd         : place the mount tree @source_mnt is attached
+ *  @parent_nd  : if non-null, detach the source_mnt from its parent and
+ *                 store the parent mount and mountpoint dentry.
+ *                 (done when source_mnt is moved)
  *
  *  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.
@@ -685,6 +688,21 @@ 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 moved to the destination.
  *
  * if the source mount is a tree, the operations explained above is
  * applied to each mount in the tree.
@@ -692,7 +710,7 @@ Enomem:
  * in allocations.
  */
 static int attach_recursive_mnt(struct vfsmount *source_mnt,
-                                struct nameidata *nd)
+                        struct nameidata *nd, struct nameidata *parent_nd)
 {
         LIST_HEAD(tree_list);
         struct vfsmount *dest_mnt = nd->mnt;
@@ -708,8 +726,14 @@ static int attach_recursive_mnt(struct vfsmount *source_mnt,
         }
 
         spin_lock(&vfsmount_lock);
-        mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
-        commit_tree(source_mnt);
+        if (parent_nd) {
+                detach_mnt(source_mnt, parent_nd);
+                attach_mnt(source_mnt, nd);
+                touch_namespace(current->namespace);
+        } else {
+                mnt_set_mountpoint(dest_mnt, dest_dentry, source_mnt);
+                commit_tree(source_mnt);
+        }
 
         list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
                 list_del_init(&child->mnt_hash);
@@ -740,7 +764,7 @@ static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
 
         err = -ENOENT;
         if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
-                err = attach_recursive_mnt(mnt, nd);
+                err = attach_recursive_mnt(mnt, nd, NULL);
 out_unlock:
         up(&nd->dentry->d_inode->i_sem);
         if (!err)
@@ -869,35 +893,36 @@ static int do_move_mount(struct nameidata *nd, char *old_name)
         if (IS_DEADDIR(nd->dentry->d_inode))
                 goto out1;
 
-        spin_lock(&vfsmount_lock);
         if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
-                goto out2;
+                goto out1;
 
         err = -EINVAL;
         if (old_nd.dentry != old_nd.mnt->mnt_root)
-                goto out2;
+                goto out1;
 
         if (old_nd.mnt == old_nd.mnt->mnt_parent)
-                goto out2;
+                goto out1;
 
         if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
               S_ISDIR(old_nd.dentry->d_inode->i_mode))
-                goto out2;
-
+                goto out1;
+        /*
+         * Don't move a mount residing in a shared parent.
+         */
+        if (old_nd.mnt->mnt_parent && IS_MNT_SHARED(old_nd.mnt->mnt_parent))
+                goto out1;
         err = -ELOOP;
         for (p = nd->mnt; p->mnt_parent != p; p = p->mnt_parent)
                 if (p == old_nd.mnt)
-                        goto out2;
-        err = 0;
+                        goto out1;
 
-        detach_mnt(old_nd.mnt, &parent_nd);
-        attach_mnt(old_nd.mnt, nd);
-        touch_namespace(current->namespace);
+        if ((err = attach_recursive_mnt(old_nd.mnt, nd, &parent_nd)))
+                goto out1;
 
+        spin_lock(&vfsmount_lock);
         /* if the mount is moved, it should no longer be expire
          * automatically */
         list_del_init(&old_nd.mnt->mnt_expire);
-out2:
         spin_unlock(&vfsmount_lock);
 out1:
         up(&nd->dentry->d_inode->i_sem);
@@ -1467,6 +1492,10 @@ asmlinkage long sys_pivot_root(const char __user * new_root,
         down_write(&namespace_sem);
         down(&old_nd.dentry->d_inode->i_sem);
         error = -EINVAL;
+        if (IS_MNT_SHARED(old_nd.mnt) ||
+                IS_MNT_SHARED(new_nd.mnt->mnt_parent) ||
+                IS_MNT_SHARED(user_nd.mnt->mnt_parent))
+                goto out2;
         if (!check_mnt(user_nd.mnt))
                 goto out2;
         error = -ENOENT;