[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>
diff --git a/fs/namespace.c b/fs/namespace.c
index f6861a5..9f5a084 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 @@
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 @@
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 @@
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 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 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 @@
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 @@
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)