From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754927AbZHCV77 (ORCPT ); Mon, 3 Aug 2009 17:59:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754886AbZHCV76 (ORCPT ); Mon, 3 Aug 2009 17:59:58 -0400 Received: from e37.co.us.ibm.com ([32.97.110.158]:60352 "EHLO e37.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754302AbZHCV75 (ORCPT ); Mon, 3 Aug 2009 17:59:57 -0400 Subject: [RFC][PATCH 1/2] pin kern mounts as writable To: Al Viro Cc: Nick Piggin , linux-kernel@vger.kernel.org, OGAWA Hirofumi , Dave Hansen From: Dave Hansen Date: Mon, 03 Aug 2009 14:59:40 -0700 Message-Id: <20090803215940.DF984602@kernel> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we are going to continue to use mnt_clone_write() inside of init_file(), then we're going to need some kind of extra handling. What I want to do in the next patch is add a debugging check in mnt_clone_write() to double-check that there *is* a real writer on the mount before mnt_clone_write() succeeds. To do that, we either need to check for MS_KERNMOUNT around that debug check, or we need to make sure that these kern mounts *have* a write already. I'm choosing to make sure they always have a write. --- linux-2.6.git-dave/fs/super.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff -puN fs/super.c~pin-mnt-writable fs/super.c --- linux-2.6.git/fs/super.c~pin-mnt-writable 2009-08-03 14:47:29.000000000 -0700 +++ linux-2.6.git-dave/fs/super.c 2009-08-03 14:49:49.000000000 -0700 @@ -948,7 +948,19 @@ EXPORT_SYMBOL_GPL(do_kern_mount); struct vfsmount *kern_mount_data(struct file_system_type *type, void *data) { - return vfs_kern_mount(type, MS_KERNMOUNT, type->name, data); + int err = 0; + struct vfsmount *mnt; + mnt = vfs_kern_mount(type, MS_KERNMOUNT, type->name, data); + if (IS_ERR(mnt)) + return mnt; + /* + * We will never allow this mount to be r/o. Doing + * this makes it explicit and allows mnt_clone_write() + * to be used unconditionally on this mount. + */ + err = mnt_want_write(mnt); + WARN_ON(err); + return mnt; } EXPORT_SYMBOL_GPL(kern_mount_data); diff -puN include/linux/mount.h~pin-mnt-writable include/linux/mount.h _