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

[Chuck Lever]

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.


-- 
Chuck Lever