Re: [PATCH v4 3/4] nfsd: implement server-stats-get netlink handler

[Chuck Lever]

On Wed, Jun 17, 2026, at 7:07 AM, Jeff Layton wrote:
> On Tue, 2026-06-16 at 20:57 -0400, Chuck Lever wrote:
>> Hey Jeff -
>> 
>> On Tue, Jun 16, 2026, at 8:45 AM, Jeff Layton wrote:
>> > Implement nfsd_nl_server_stats_get_dumpit() which exposes the
>> > NFS server statistics currently available via /proc/net/rpc/nfsd
>> > through the nfsd generic netlink family.
>> > 
>> > The handler uses a dump operation to stream statistics across
>> > multiple netlink messages:
>> > 
>> >   - First message: all scalar stats (reply cache, filehandle,
>> >     IO, network, RPC) plus per-version procedure counts
>> >     (proc2/3/4-ops) using per-netns vs_count arrays.
>> > 
>> >   - Subsequent messages: NFSv4 per-operation counts
>> >     (proc4ops-ops), one entry per message, using cb->args[0]
>> >     to track the current operation index across dump calls.
>> > 
>> > This allows nfsstat to retrieve server statistics via netlink
>> > with a procfs fallback for older kernels.
>> > 
>> > Assisted-by: Claude:claude-opus-4-6
>> > Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
>> > ---
>> >  Documentation/netlink/specs/nfsd.yaml | 105 +++++++++++++++++
>> >  fs/nfsd/netlink.c                     |   5 +
>> >  fs/nfsd/netlink.h                     |   2 +
>> >  fs/nfsd/nfsctl.c                      | 206 ++++++++++++++++++++++++++++++++++
>> >  include/uapi/linux/nfsd_netlink.h     |  35 ++++++
>> >  5 files changed, 353 insertions(+)
>> 
>> The procfs output in nfsd_show() emits one more counter that this dump
>> handler drops: wdeleg_getattr (NFSD_STATS_WDELEG_GETATTR), printed at
>> the end of the CONFIG_NFSD_V4 block in fs/nfsd/stats.c, right after
>> proc4ops. The netlink dump stops after proc4ops-ops and sets
>> cb->args[0] = -1, so the write-delegation GETATTR-conflict counter never
>> goes out on the wire.
>> 
>> There's no schema slot for it either: the server-stats attribute-set
>> ends at proc4ops-ops, so a consumer that prefers netlink and only falls
>> back to procfs on an old kernel loses this counter on every kernel new
>> enough to support server-stats-get.
>> 
>> I Suggest:
>> 
>> - add a wdeleg-getattr (u64) attribute to the server-stats
>>   attribute-set in nfsd.yaml and list it under the dump reply
>>   attributes;
>> 
>> - add NFSD_A_SERVER_STATS_WDELEG_GETATTR to the uapi enum, after
>>   PROC4OPS_OPS and before __NFSD_A_SERVER_STATS_MAX so existing
>>   values don't shift;
>> 
>> - emit it as a single scalar in the start == 0 message, wrapped in
>>   CONFIG_NFSD_V4 to match the procfs side.
>> 
>
> This omission was intentional. The stated purpose of this patchset was
> to convert nfsstat to use netlink. nfsstat does not access or display
> this field today. Without something that consumes this stat, I don't
> see the point of adding it here. We can always add it later when/if it
> becomes useful to userland.

If we were adding a greenfield kernel-userspace API, I would agree.
However, this API is meant to be compatible with the existing
procfs API, so it should match to prevent a regression (I'm not
aware of a consumer, this is only a general guideline).

For future reference: since a missing feature cannot be expressed
in a patch's diff body, your intention to exclude this field could
be mentioned in the commit message.


> Is there something that accesses this today that I'm not aware of? If
> not, is there some future intent to add this to nfsstat?

I think nfsstat should display the wdeleg-getattr field. It has simply
been forgotten.


-- 
Chuck Lever