From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752162AbcJCAvP (ORCPT ); Sun, 2 Oct 2016 20:51:15 -0400 Received: from out4-smtp.messagingengine.com ([66.111.4.28]:56941 "EHLO out4-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751621AbcJCAqh (ORCPT ); Sun, 2 Oct 2016 20:46:37 -0400 X-Sasl-enc: Dlqo8Va5sHh/X0Ssa3pcBJUUoniggDTOhHJ8olO/HbKl 1475455595 Subject: [RFC PATCH 2/8] vfs - add path_is_mountpoint() helper From: Ian Kent To: Kernel Mailing List Cc: autofs mailing list , Al Viro , linux-fsdevel , Omar Sandoval , Andrew Morton , "Eric W. Biederman" Date: Mon, 03 Oct 2016 08:46:33 +0800 Message-ID: <20161003004633.4865.1482.stgit@pluto.themaw.net> In-Reply-To: <20161003003646.4865.42500.stgit@pluto.themaw.net> References: <20161003003646.4865.42500.stgit@pluto.themaw.net> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Ian Kent d_mountpoint() can only be used reliably to establish if a dentry is not mounted in any namespace. It isn't aware of the possibility there may be multiple mounts using a given dentry that may be in a different namespace. Add helper functions, path_is_mountpoint() and an rcu version , that checks if a struct path is a mountpoint for this case. Signed-off-by: Ian Kent Cc: Al Viro Cc: Eric W. Biederman Cc: Omar Sandoval --- fs/namespace.c | 43 +++++++++++++++++++++++++++++++++++++++++++ include/linux/fs.h | 2 ++ 2 files changed, 45 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 7bb2cda..ca1faaa 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1153,6 +1153,49 @@ struct vfsmount *mntget(struct vfsmount *mnt) } EXPORT_SYMBOL(mntget); +static bool __path_is_mountpoint(struct path *path) +{ + struct mount *mount; + struct vfsmount *mnt; + unsigned seq; + + do { + seq = read_seqbegin(&mount_lock); + mount = __lookup_mnt(path->mnt, path->dentry); + mnt = mount ? &mount->mnt : NULL; + } while (mnt && + !(mnt->mnt_flags & MNT_SYNC_UMOUNT) && + read_seqretry(&mount_lock, seq)); + + return mnt != NULL; +} + +/* Check if path is a mount in current namespace */ +bool path_is_mountpoint(struct path *path) +{ + bool res; + + if (!d_mountpoint(path->dentry)) + return 0; + + rcu_read_lock(); + res = __path_is_mountpoint(path); + rcu_read_unlock(); + + return res; +} +EXPORT_SYMBOL(path_is_mountpoint); + +/* Check if path is a mount in current namespace */ +bool path_is_mountpoint_rcu(struct path *path) +{ + if (!d_mountpoint(path->dentry)) + return 0; + + return __path_is_mountpoint(path); +} +EXPORT_SYMBOL(path_is_mountpoint_rcu); + struct vfsmount *mnt_clone_internal(struct path *path) { struct mount *p; diff --git a/include/linux/fs.h b/include/linux/fs.h index 901e25d..d588b26 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2117,6 +2117,8 @@ extern int vfs_ustat(dev_t, struct kstatfs *); extern int freeze_super(struct super_block *super); extern int thaw_super(struct super_block *super); extern bool our_mnt(struct vfsmount *mnt); +extern bool path_is_mountpoint(struct path *); +extern bool path_is_mountpoint_rcu(struct path *); extern int current_umask(void);