Return-Path: Received: from mx2.netapp.com ([216.240.18.37]:53898 "EHLO mx2.netapp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753579Ab1H2OzT (ORCPT ); Mon, 29 Aug 2011 10:55:19 -0400 Message-ID: <4E5BA855.2030109@netapp.com> Date: Mon, 29 Aug 2011 10:55:17 -0400 From: Bryan Schumaker To: Chuck Lever CC: "linux-nfs@vger.kernel.org" , "Myklebust, Trond" Subject: Re: [PATCH] NFS: Add "device" tag to /proc/self/mountstats References: <4E5807A8.2020600@netapp.com> <6701215B-7718-4EE2-9EC4-BFE0936B0D2A@oracle.com> <4E5B981A.1020605@netapp.com> <7F5CA899-5277-4F74-A10F-8F889347F445@oracle.com> In-Reply-To: <7F5CA899-5277-4F74-A10F-8F889347F445@oracle.com> Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 On 08/29/2011 10:43 AM, Chuck Lever wrote: > > On Aug 29, 2011, at 9:46 AM, Bryan Schumaker wrote: > >> On 08/27/2011 07:52 PM, Chuck Lever wrote: >>> >>> On Aug 26, 2011, at 4:52 PM, Bryan Schumaker wrote: >>> >>>> nfsiostat was failing to find mounted filesystems on recent kernels due >>>> to changes in the VFS that resulted in a missing "device" tag in the >>>> /proc/self/mountstats file. >>> >>> What was the commit ID that changed this formal kernel API? I'd like to see the justification. >> >> It was changed by this commit: >> >> commit c7f404b40a3665d9f4e9a927cc5c1ee0479ed8f9 >> Author: Al Viro >> Date: Wed Mar 16 06:59:40 2011 -0400 >> >> vfs: new superblock methods to override /proc/*/mount{s,info} >> >> a) ->show_devname(m, mnt) - what to put into devname columns in mounts, >> mountinfo and mountstats >> b) ->show_path(m, mnt) - what to put into relative path column in mountinfo >> >> Leaving those NULL gives old behaviour. NFS switched to using those. >> >> Signed-off-by: Al Viro > > It looks like dropping the "device" tag from /proc/self/mountstats was not intentional, so this is a kernel API regression. At a guess, 2.6.39 probably works right, but 3.0 is broken. Whatever solution we come up with might need to be cc:d to stable@kernel.org. Be sure to verify which released kernels are broken. I'll double check that 39 works. > > Does changing nfs_show_devname() to add a "device" tag have any effect on the other two /proc files (mounts and mountinfo)? I suspect you do want to fix show_vfsstat() instead of nfs_show_devname(). This should add "device" only where it is needed, and would work for all file systems. Yeah, looks like it changes both. I'm looking at show_vfsstat() now, but nfs_show_devname() will return an error if a call to nfs_path() fails. This would probably result in an empty "device " line printed to /proc/self/mountstats. Do you know if that would be a problem for anything? I'm thinking about doing something like this: diff --git a/fs/namespace.c b/fs/namespace.c index 22bfe82..1429114 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1109,6 +1109,7 @@ static int show_vfsstat(struct seq_file *m, void *v) /* device */ if (mnt->mnt_sb->s_op->show_devname) { + seq_puts(m, "device "); err = mnt->mnt_sb->s_op->show_devname(m, mnt); } else { if (mnt->mnt_devname) { > >> >> >>> >>>> This patch re-adds the "device" tag for NFS >>>> mount data in /proc/self/mountstats. >>> >>> The purpose of mountstats is to be an interface that all file systems can use. If we can't add "device" back to all mounts listed in /proc/self/mountstats, it might be better to adjust nfsiostats to cope. >>> >>>> Signed-off-by: Bryan Schumaker >>>> --- >>>> fs/nfs/super.c | 4 +++- >>>> 1 files changed, 3 insertions(+), 1 deletions(-) >>>> >>>> diff --git a/fs/nfs/super.c b/fs/nfs/super.c >>>> index b961cea..e6a0317 100644 >>>> --- a/fs/nfs/super.c >>>> +++ b/fs/nfs/super.c >>>> @@ -766,8 +766,10 @@ static int nfs_show_devname(struct seq_file *m, struct vfsmount *mnt) >>>> devname = nfs_path(&dummy, mnt->mnt_root, page, PAGE_SIZE); >>>> if (IS_ERR(devname)) >>>> err = PTR_ERR(devname); >>>> - else >>>> + else { >>>> + seq_puts(m, "device "); >>>> seq_escape(m, devname, " \t\n\\"); >>>> + } >>>> free_page((unsigned long)page); >>>> return err; >>>> } >>>> -- >>>> 1.7.6 >>> >> >