new helper: mount_subtree()
takes vfsmount and relative path, does lookup within that vfsmount
(possibly triggering automounts) and returns the result as root
of subtree suitable for return by ->mount() (i.e. a reference to
dentry and an active reference to its superblock grabbed, superblock
locked exclusive).
btrfs and nfs switched to it instead of open-coding the sucker.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index cfbedd7..17ee7fc 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -825,13 +825,9 @@
static struct dentry *mount_subvol(const char *subvol_name, int flags,
const char *device_name, char *data)
{
- struct super_block *s;
struct dentry *root;
struct vfsmount *mnt;
- struct mnt_namespace *ns_private;
char *newargs;
- struct path path;
- int error;
newargs = setup_root_args(data);
if (!newargs)
@@ -842,36 +838,17 @@
if (IS_ERR(mnt))
return ERR_CAST(mnt);
- ns_private = create_mnt_ns(mnt);
- if (IS_ERR(ns_private))
- return ERR_CAST(ns_private);
+ root = mount_subtree(mnt, subvol_name);
- /*
- * This will trigger the automount of the subvol so we can just
- * drop the mnt we have here and return the dentry that we
- * found.
- */
- error = vfs_path_lookup(mnt->mnt_root, mnt, subvol_name,
- LOOKUP_FOLLOW, &path);
- put_mnt_ns(ns_private);
- if (error)
- return ERR_PTR(error);
-
- if (!is_subvolume_inode(path.dentry->d_inode)) {
- path_put(&path);
- error = -EINVAL;
+ if (!IS_ERR(root) && !is_subvolume_inode(root->d_inode)) {
+ struct super_block *s = root->d_sb;
+ dput(root);
+ root = ERR_PTR(-EINVAL);
+ deactivate_locked_super(s);
printk(KERN_ERR "btrfs: '%s' is not a valid subvolume\n",
subvol_name);
- return ERR_PTR(-EINVAL);
}
- /* Get a ref to the sb and the dentry we found and return it */
- s = path.mnt->mnt_sb;
- atomic_inc(&s->s_active);
- root = dget(path.dentry);
- path_put(&path);
- down_write(&s->s_umount);
-
return root;
}
diff --git a/fs/namespace.c b/fs/namespace.c
index aea4b768..50ee303 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2490,6 +2490,34 @@
}
EXPORT_SYMBOL(create_mnt_ns);
+struct dentry *mount_subtree(struct vfsmount *mnt, const char *name)
+{
+ struct mnt_namespace *ns;
+ struct path path;
+ int err;
+
+ ns = create_mnt_ns(mnt);
+ if (IS_ERR(ns))
+ return ERR_CAST(ns);
+
+ err = vfs_path_lookup(mnt->mnt_root, mnt,
+ name, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT, &path);
+
+ put_mnt_ns(ns);
+
+ if (err)
+ return ERR_PTR(err);
+
+ /* trade a vfsmount reference for active sb one */
+ atomic_inc(&path.mnt->mnt_sb->s_active);
+ mntput(path.mnt);
+ /* lock the sucker */
+ down_write(&path.mnt->mnt_sb->s_umount);
+ /* ... and return the root of (sub)tree on it */
+ return path.dentry;
+}
+EXPORT_SYMBOL(mount_subtree);
+
SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
char __user *, type, unsigned long, flags, void __user *, data)
{
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 46d69f38..1347774 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2787,35 +2787,17 @@
static struct dentry *nfs_follow_remote_path(struct vfsmount *root_mnt,
const char *export_path)
{
- struct mnt_namespace *ns_private;
- struct super_block *s;
struct dentry *dentry;
- struct path path;
- int ret;
+ int ret = nfs_referral_loop_protect();
- ns_private = create_mnt_ns(root_mnt);
- if (IS_ERR(ns_private))
- return ERR_CAST(ns_private);
-
- ret = nfs_referral_loop_protect();
- if (ret == 0) {
- ret = vfs_path_lookup(root_mnt->mnt_root, root_mnt,
- export_path, LOOKUP_FOLLOW|LOOKUP_AUTOMOUNT,
- &path);
- nfs_referral_loop_unprotect();
+ if (ret) {
+ mntput(root_mnt);
+ return ERR_PTR(ret);
}
- put_mnt_ns(ns_private);
+ dentry = mount_subtree(root_mnt, export_path);
+ nfs_referral_loop_unprotect();
- if (ret != 0)
- return ERR_PTR(ret);
-
- s = path.mnt->mnt_sb;
- atomic_inc(&s->s_active);
- dentry = dget(path.dentry);
-
- path_put(&path);
- down_write(&s->s_umount);
return dentry;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 0c4df26..e313022 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1886,6 +1886,7 @@
extern struct dentry *mount_nodev(struct file_system_type *fs_type,
int flags, void *data,
int (*fill_super)(struct super_block *, void *, int));
+extern struct dentry *mount_subtree(struct vfsmount *mnt, const char *path);
void generic_shutdown_super(struct super_block *sb);
void kill_block_super(struct super_block *sb);
void kill_anon_super(struct super_block *sb);