[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, 105 insertions, 21 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index f6861a5487df..9f5a084b239f 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -28,8 +28,6 @@
 
 extern int __init init_rootfs(void);
 
-#define CL_EXPIRE       0x01
-
 #ifdef CONFIG_SYSFS
 extern int __init sysfs_init(void);
 #else
@@ -145,13 +143,43 @@ static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
         old_nd->dentry->d_mounted--;
 }
 
+void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry,
+                        struct vfsmount *child_mnt)
+{
+        child_mnt->mnt_parent = mntget(mnt);
+        child_mnt->mnt_mountpoint = dget(dentry);
+        dentry->d_mounted++;
+}
+
 static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
 {
-        mnt->mnt_parent = mntget(nd->mnt);
-        mnt->mnt_mountpoint = dget(nd->dentry);
-        list_add(&mnt->mnt_hash, mount_hashtable + hash(nd->mnt, nd->dentry));
+        mnt_set_mountpoint(nd->mnt, nd->dentry, mnt);
+        list_add_tail(&mnt->mnt_hash, mount_hashtable +
+                        hash(nd->mnt, nd->dentry));
         list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
-        nd->dentry->d_mounted++;
+}
+
+/*
+ * the caller must hold vfsmount_lock
+ */
+static void commit_tree(struct vfsmount *mnt)
+{
+        struct vfsmount *parent = mnt->mnt_parent;
+        struct vfsmount *m;
+        LIST_HEAD(head);
+        struct namespace *n = parent->mnt_namespace;
+
+        BUG_ON(parent == mnt);
+
+        list_add_tail(&head, &mnt->mnt_list);
+        list_for_each_entry(m, &head, mnt_list)
+                m->mnt_namespace = n;
+        list_splice(&head, n->list.prev);
+
+        list_add_tail(&mnt->mnt_hash, mount_hashtable +
+                                hash(parent, mnt->mnt_mountpoint));
+        list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
+        touch_namespace(n);
 }
 
 static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
@@ -183,7 +211,11 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
                 mnt->mnt_root = dget(root);
                 mnt->mnt_mountpoint = mnt->mnt_root;
                 mnt->mnt_parent = mnt;
-                mnt->mnt_namespace = current->namespace;
+
+                if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
+                        list_add(&mnt->mnt_share, &old->mnt_share);
+                if (flag & CL_MAKE_SHARED)
+                        set_mnt_shared(mnt);
 
                 /* stick the duplicate mount on the same expiry list
                  * as the original if that was on one */
@@ -379,7 +411,7 @@ int may_umount(struct vfsmount *mnt)
 
 EXPORT_SYMBOL(may_umount);
 
-static void release_mounts(struct list_head *head)
+void release_mounts(struct list_head *head)
 {
         struct vfsmount *mnt;
         while(!list_empty(head)) {
@@ -401,7 +433,7 @@ static void release_mounts(struct list_head *head)
         }
 }
 
-static void umount_tree(struct vfsmount *mnt, struct list_head *kill)
+void umount_tree(struct vfsmount *mnt, struct list_head *kill)
 {
         struct vfsmount *p;
 
@@ -581,7 +613,7 @@ static int lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
         }
 }
 
-static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
+struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry,
                                         int flag)
 {
         struct vfsmount *res, *p, *q, *r, *s;
@@ -626,6 +658,67 @@ Enomem:
         return NULL;
 }
 
+/*
+ *  @source_mnt : mount tree to be attached
+ *  @nd        : place the mount tree @source_mnt is attached
+ *
+ *  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   |
+ *      *********************************************
+ * A bind operation clones the source mount and mounts the clone on the
+ * destination mount.
+ *
+ * (++)  the cloned mount is propagated to all the mounts in the propagation
+ *       tree of the destination mount and the cloned mount is added to
+ *       the peer group of the source mount.
+ * (+)   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.
+ *
+ * if the source mount is a tree, the operations explained above is
+ * applied to each mount in the tree.
+ * Must be called without spinlocks held, since this function can sleep
+ * in allocations.
+ */
+static int attach_recursive_mnt(struct vfsmount *source_mnt,
+                                struct nameidata *nd)
+{
+        LIST_HEAD(tree_list);
+        struct vfsmount *dest_mnt = nd->mnt;
+        struct dentry *dest_dentry = nd->dentry;
+        struct vfsmount *child, *p;
+
+        if (propagate_mnt(dest_mnt, dest_dentry, source_mnt, &tree_list))
+                return -EINVAL;
+
+        if (IS_MNT_SHARED(dest_mnt)) {
+                for (p = source_mnt; p; p = next_mnt(p, source_mnt))
+                        set_mnt_shared(p);
+        }
+
+        spin_lock(&vfsmount_lock);
+        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);
+                commit_tree(child);
+        }
+        spin_unlock(&vfsmount_lock);
+        return 0;
+}
+
 static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
 {
         int err;
@@ -646,17 +739,8 @@ static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
                 goto out_unlock;
 
         err = -ENOENT;
-        spin_lock(&vfsmount_lock);
-        if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry)) {
-                struct list_head head;
-
-                attach_mnt(mnt, nd);
-                list_add_tail(&head, &mnt->mnt_list);
-                list_splice(&head, current->namespace->list.prev);
-                err = 0;
-                touch_namespace(current->namespace);
-        }
-        spin_unlock(&vfsmount_lock);
+        if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry))
+                err = attach_recursive_mnt(mnt, nd);
 out_unlock:
         up(&nd->dentry->d_inode->i_sem);
         if (!err)