From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756853Ab2BAW66 (ORCPT ); Wed, 1 Feb 2012 17:58:58 -0500 Received: from out3-smtp.messagingengine.com ([66.111.4.27]:49110 "EHLO out3-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754354Ab2BAW65 (ORCPT ); Wed, 1 Feb 2012 17:58:57 -0500 X-Sasl-enc: 2LQ46RCaaKSpJ/ogzGg1XcnIH2RBi2S5WiGafhZMa76L 1328137136 Date: Wed, 1 Feb 2012 14:49:18 -0800 From: Greg Kroah-Hartman To: "Eric W. Biederman" Cc: Jiri Slaby , Alan Cox , LKML , Al Viro , Linus Torvalds , Maciej Rutecki Subject: Re: [PATCH] sysfs: Optionally count subdirectories to support buggy applications Message-ID: <20120201224918.GA2868@kroah.com> References: <20120130221059.26ab5edf@pyramind.ukuu.org.uk> <20120130222717.GA6393@kroah.com> <4F27C6EB.2070305@suse.cz> <20120201222441.GB2333@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 01, 2012 at 02:44:32PM -0800, Eric W. Biederman wrote: > Greg Kroah-Hartman writes: > > > On Wed, Feb 01, 2012 at 02:21:59PM -0800, Eric W. Biederman wrote: > >> > >> lm_sensors and possibly other applications get confused if all sysfs > >> directories return nlink == 1. The lm_sensors code that got confused > >> was just wrong and a fixed version of lm_sensors should be released > >> shortly. > >> > >> There may be other applications that have problems with sysfs return > >> nlink == 1 for directories. To allow people to continue to use old > >> versions of userspace with new kernels add to sysfs a compile time > >> option to maintain mostly precise directory counts for those people who > >> don't mind the cost. > >> > >> I have moved where we keep nlink in sysfs_dirent as compared to previous > >> versions of subdirectory counting to a location that packs better. > >> > >> Signed-off-by: Eric W. Biederman > >> --- > >> fs/sysfs/Kconfig | 15 +++++++++++++++ > >> fs/sysfs/dir.c | 8 ++++++++ > >> fs/sysfs/inode.c | 2 ++ > >> fs/sysfs/sysfs.h | 38 ++++++++++++++++++++++++++++++++++++++ > >> 4 files changed, 63 insertions(+), 0 deletions(-) > >> > >> diff --git a/fs/sysfs/Kconfig b/fs/sysfs/Kconfig > >> index 8c41fea..9b403e9 100644 > >> --- a/fs/sysfs/Kconfig > >> +++ b/fs/sysfs/Kconfig > >> @@ -21,3 +21,18 @@ config SYSFS > >> example, "root=03:01" for /dev/hda1. > >> > >> Designers of embedded systems may wish to say N here to conserve space. > >> + > >> +config SYSFS_COUNT_LINKS > >> + bool "sysfs count subdirectoires to support buggy applications" > >> + default n > > > > As we don't want to break things, this should be default y, right? > > The new behavior is backwards compatible. What the new behavior is not > is bug compatible. So nothing *should* break. "should", but you really don't know, as all we have is one report so far. > Furthermore the breaking we have seen so far is limited to just > lm_sensors. That is exactly one program that is not a server failing to > start. That seems pretty minor in the worst case. > > So I really don't expect anyone who ships 3.4 to enable this option. What about users who use a new kernel on old userspace, which happens all the time (i.e. all the kernel developers themselves)? > I have written the option solely so that in case my assessment turns out > to be wrong there is already a tested solution. I have been through the > pain of not being able to upgrade/test a new kernel because of a > backwards incompatible change and it can be very unpleasant. I'd really prefer this to be default 'y', and if a distro knows it can turn it off to save time/space, it can. thanks, greg k-h