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new helper: mount_subtree()

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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>
This commit is contained in:
Al Viro
2011-11-16 21:43:59 -05:00
parent c133449587
commit ea441d1104
4 changed files with 41 additions and 53 deletions
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30
fs/nfs/super.c
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@@ -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;
}