[PATCH] new helpers - collect_mounts() and release_collected_mounts()

Get a snapshot of a subtree, creating private clones of vfsmounts
for all its components and release such snapshot resp.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 24 insertions, 1 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 860752998fb3..06083885b21e 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -246,7 +246,7 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
                         list_add(&mnt->mnt_slave, &old->mnt_slave_list);
                         mnt->mnt_master = old;
                         CLEAR_MNT_SHARED(mnt);
-                } else {
+                } else if (!(flag & CL_PRIVATE)) {
                         if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
                                 list_add(&mnt->mnt_share, &old->mnt_share);
                         if (IS_MNT_SLAVE(old))
@@ -746,6 +746,26 @@ Enomem:
         return NULL;
 }
 
+struct vfsmount *collect_mounts(struct vfsmount *mnt, struct dentry *dentry)
+{
+        struct vfsmount *tree;
+        down_read(&namespace_sem);
+        tree = copy_tree(mnt, dentry, CL_COPY_ALL | CL_PRIVATE);
+        up_read(&namespace_sem);
+        return tree;
+}
+
+void drop_collected_mounts(struct vfsmount *mnt)
+{
+        LIST_HEAD(umount_list);
+        down_read(&namespace_sem);
+        spin_lock(&vfsmount_lock);
+        umount_tree(mnt, 0, &umount_list);
+        spin_unlock(&vfsmount_lock);
+        up_read(&namespace_sem);
+        release_mounts(&umount_list);
+}
+
 /*
  *  @source_mnt : mount tree to be attached
  *  @nd         : place the mount tree @source_mnt is attached
diff --git a/fs/pnode.h b/fs/pnode.h
index d45bd8ec36bf..f249be2fee7a 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -22,6 +22,7 @@
 #define CL_COPY_ALL             0x04
 #define CL_MAKE_SHARED          0x08
 #define CL_PROPAGATION          0x10
+#define CL_PRIVATE              0x20
 
 static inline void set_mnt_shared(struct vfsmount *mnt)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 1bcce660cf03..50078bb30a1c 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1470,6 +1470,8 @@ extern long do_mount(char *, char *, char *, unsigned long, void *);
 extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int);
 extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *,
                                   struct vfsmount *);
+extern struct vfsmount *collect_mounts(struct vfsmount *, struct dentry *);
+extern void drop_collected_mounts(struct vfsmount *);
 
 extern int vfs_statfs(struct dentry *, struct kstatfs *);