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Commit ea441d11 authored by Al Viro's avatar Al Viro
Browse files

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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent c1334495

fs/btrfs/super.c

+6 −29
Original line number Diff line number Diff line
@@ -825,13 +825,9 @@ static char *setup_root_args(char *args) 
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 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags, 
	if (IS_ERR(mnt))

		return ERR_CAST(mnt);



	ns_private = create_mnt_ns(mnt);

	if (IS_ERR(ns_private))

		return ERR_CAST(ns_private);



	/*

	 * 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);

	root = mount_subtree(mnt, subvol_name);



	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;

}

fs/namespace.c

+28 −0
Original line number Diff line number Diff line
@@ -2490,6 +2490,34 @@ struct mnt_namespace *create_mnt_ns(struct vfsmount *mnt) 
}

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)

{

fs/nfs/super.c

+6 −24
Original line number Diff line number Diff line
@@ -2787,35 +2787,17 @@ static void nfs_referral_loop_unprotect(void) 
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;



	ns_private = create_mnt_ns(root_mnt);

	if (IS_ERR(ns_private))

		return ERR_CAST(ns_private);

	int ret = nfs_referral_loop_protect();



	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();

	}



	put_mnt_ns(ns_private);



	if (ret != 0)

	if (ret) {

		mntput(root_mnt);

		return ERR_PTR(ret);

	}



	s = path.mnt->mnt_sb;

	atomic_inc(&s->s_active);

	dentry = dget(path.dentry);

	dentry = mount_subtree(root_mnt, export_path);

	nfs_referral_loop_unprotect();



	path_put(&path);

	down_write(&s->s_umount);

	return dentry;

}

include/linux/fs.h

+1 −0
Original line number Diff line number Diff line
@@ -1886,6 +1886,7 @@ extern struct dentry *mount_single(struct file_system_type *fs_type, 
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);