[PATCH] shared mount handling: bind and rbind

Implement handling of MS_BIND 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, 80 insertions, 1 deletions

diff --git a/fs/pnode.c b/fs/pnode.c
index 1e22165ea41f..2d572b88e6f6 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -20,9 +20,88 @@ static inline struct vfsmount *next_peer(struct vfsmount *p)
 void change_mnt_propagation(struct vfsmount *mnt, int type)
 {
         if (type == MS_SHARED) {
-                mnt->mnt_flags |= MNT_SHARED;
+                set_mnt_shared(mnt);
         } else {
                 list_del_init(&mnt->mnt_share);
                 mnt->mnt_flags &= ~MNT_PNODE_MASK;
         }
 }
+
+/*
+ * get the next mount in the propagation tree.
+ * @m: the mount seen last
+ * @origin: the original mount from where the tree walk initiated
+ */
+static struct vfsmount *propagation_next(struct vfsmount *m,
+                                         struct vfsmount *origin)
+{
+        m = next_peer(m);
+        if (m == origin)
+                return NULL;
+        return m;
+}
+
+/*
+ * mount 'source_mnt' under the destination 'dest_mnt' at
+ * dentry 'dest_dentry'. And propagate that mount to
+ * all the peer and slave mounts of 'dest_mnt'.
+ * Link all the new mounts into a propagation tree headed at
+ * source_mnt. Also link all the new mounts using ->mnt_list
+ * headed at source_mnt's ->mnt_list
+ *
+ * @dest_mnt: destination mount.
+ * @dest_dentry: destination dentry.
+ * @source_mnt: source mount.
+ * @tree_list : list of heads of trees to be attached.
+ */
+int propagate_mnt(struct vfsmount *dest_mnt, struct dentry *dest_dentry,
+                    struct vfsmount *source_mnt, struct list_head *tree_list)
+{
+        struct vfsmount *m, *child;
+        int ret = 0;
+        struct vfsmount *prev_dest_mnt = dest_mnt;
+        struct vfsmount *prev_src_mnt  = source_mnt;
+        LIST_HEAD(tmp_list);
+        LIST_HEAD(umount_list);
+
+        for (m = propagation_next(dest_mnt, dest_mnt); m;
+                        m = propagation_next(m, dest_mnt)) {
+                int type = CL_PROPAGATION;
+
+                if (IS_MNT_NEW(m))
+                        continue;
+
+                if (IS_MNT_SHARED(m))
+                        type |= CL_MAKE_SHARED;
+
+                if (!(child = copy_tree(source_mnt, source_mnt->mnt_root,
+                                                type))) {
+                        ret = -ENOMEM;
+                        list_splice(tree_list, tmp_list.prev);
+                        goto out;
+                }
+
+                if (is_subdir(dest_dentry, m->mnt_root)) {
+                        mnt_set_mountpoint(m, dest_dentry, child);
+                        list_add_tail(&child->mnt_hash, tree_list);
+                } else {
+                        /*
+                         * This can happen if the parent mount was bind mounted
+                         * on some subdirectory of a shared/slave mount.
+                         */
+                        list_add_tail(&child->mnt_hash, &tmp_list);
+                }
+                prev_dest_mnt = m;
+                prev_src_mnt  = child;
+        }
+out:
+        spin_lock(&vfsmount_lock);
+        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);
+        }
+        spin_unlock(&vfsmount_lock);
+        release_mounts(&umount_list);
+        return ret;
+}