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 <viro@xxxxxxxxxxxxxxxxxx>
> 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 <viro@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxx. 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 <bjschuma@xxxxxxxxxx>
>>> ---
>>> 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
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