Return-Path: Received: from rcsinet15.oracle.com ([148.87.113.117]:61984 "EHLO rcsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751580Ab1H2Onx convert rfc822-to-8bit (ORCPT ); Mon, 29 Aug 2011 10:43:53 -0400 Subject: Re: [PATCH] NFS: Add "device" tag to /proc/self/mountstats Content-Type: text/plain; charset=us-ascii From: Chuck Lever In-Reply-To: <4E5B981A.1020605@netapp.com> Date: Mon, 29 Aug 2011 10:43:42 -0400 Cc: "linux-nfs@vger.kernel.org" , "Myklebust, Trond" Message-Id: <7F5CA899-5277-4F74-A10F-8F889347F445@oracle.com> References: <4E5807A8.2020600@netapp.com> <6701215B-7718-4EE2-9EC4-BFE0936B0D2A@oracle.com> <4E5B981A.1020605@netapp.com> To: Bryan Schumaker Sender: linux-nfs-owner@vger.kernel.org List-ID: MIME-Version: 1.0 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. 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. > > >> >>> 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 >> > -- Chuck Lever chuck[dot]lever[at]oracle[dot]com