From ea441d1104cf1efb471fa81bc91e9fd1e6ae29fd Mon Sep 17 00:00:00 2001 From: Al Viro Date: Wed, 16 Nov 2011 21:43:59 -0500 Subject: [PATCH] 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 --- fs/btrfs/super.c | 35 ++++++----------------------------- fs/namespace.c | 28 ++++++++++++++++++++++++++++ fs/nfs/super.c | 30 ++++++------------------------ include/linux/fs.h | 1 + 4 files changed, 41 insertions(+), 53 deletions(-) diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index cfbedd7755b0..17ee7fc5e64e 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -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); + 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 aea4b7689840..50ee30345b4f 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -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) { diff --git a/fs/nfs/super.c b/fs/nfs/super.c index 46d69f38fd55..134777406ee3 100644 --- a/fs/nfs/super.c +++ b/fs/nfs/super.c @@ -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; + 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 0c4df261af7e..e3130220ce3e 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -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);