[PATCH] shared mounts handling: umount

An unmount of a mount creates a umount event on the parent.  If the
parent is a shared mount, it gets propagated to all mounts in the peer
group.

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, 86 insertions, 1 deletions

diff --git a/fs/pnode.c b/fs/pnode.c
index 2d572b88e6f6..7bc942d047cd 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -99,9 +99,94 @@ out:
         while (!list_empty(&tmp_list)) {
                 child = list_entry(tmp_list.next, struct vfsmount, mnt_hash);
                 list_del_init(&child->mnt_hash);
-                umount_tree(child, &umount_list);
+                umount_tree(child, 0, &umount_list);
         }
         spin_unlock(&vfsmount_lock);
         release_mounts(&umount_list);
         return ret;
 }
+
+/*
+ * return true if the refcount is greater than count
+ */
+static inline int do_refcount_check(struct vfsmount *mnt, int count)
+{
+        int mycount = atomic_read(&mnt->mnt_count);
+        return (mycount > count);
+}
+
+/*
+ * check if the mount 'mnt' can be unmounted successfully.
+ * @mnt: the mount to be checked for unmount
+ * NOTE: unmounting 'mnt' would naturally propagate to all
+ * other mounts its parent propagates to.
+ * Check if any of these mounts that **do not have submounts**
+ * have more references than 'refcnt'. If so return busy.
+ */
+int propagate_mount_busy(struct vfsmount *mnt, int refcnt)
+{
+        struct vfsmount *m, *child;
+        struct vfsmount *parent = mnt->mnt_parent;
+        int ret = 0;
+
+        if (mnt == parent)
+                return do_refcount_check(mnt, refcnt);
+
+        /*
+         * quickly check if the current mount can be unmounted.
+         * If not, we don't have to go checking for all other
+         * mounts
+         */
+        if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
+                return 1;
+
+        for (m = propagation_next(parent, parent); m;
+                        m = propagation_next(m, parent)) {
+                child = __lookup_mnt(m, mnt->mnt_mountpoint, 0);
+                if (child && list_empty(&child->mnt_mounts) &&
+                    (ret = do_refcount_check(child, 1)))
+                        break;
+        }
+        return ret;
+}
+
+/*
+ * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
+ * parent propagates to.
+ */
+static void __propagate_umount(struct vfsmount *mnt)
+{
+        struct vfsmount *parent = mnt->mnt_parent;
+        struct vfsmount *m;
+
+        BUG_ON(parent == mnt);
+
+        for (m = propagation_next(parent, parent); m;
+                        m = propagation_next(m, parent)) {
+
+                struct vfsmount *child = __lookup_mnt(m,
+                                        mnt->mnt_mountpoint, 0);
+                /*
+                 * umount the child only if the child has no
+                 * other children
+                 */
+                if (child && list_empty(&child->mnt_mounts)) {
+                        list_del(&child->mnt_hash);
+                        list_add_tail(&child->mnt_hash, &mnt->mnt_hash);
+                }
+        }
+}
+
+/*
+ * collect all mounts that receive propagation from the mount in @list,
+ * and return these additional mounts in the same list.
+ * @list: the list of mounts to be unmounted.
+ */
+int propagate_umount(struct list_head *list)
+{
+        struct vfsmount *mnt;
+
+        list_for_each_entry(mnt, list, mnt_hash)
+                __propagate_umount(mnt);
+        return 0;
+}