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nfsd: implement server-stats-get netlink handler

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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 one
or more netlink messages. The reply is divided into sections that
are emitted in order:

  - scalar stats (reply cache, filehandle, IO, network, RPC),
    emitted once in the first message, then

  - per-version procedure counts (proc2/3/4-ops) and the NFSv4
    per-operation counts (proc4ops-ops), using the per-netns
    vs_count arrays.

cb->args[0] tracks the current section and cb->args[1] the entry
index within it, so a section that does not fit in the current
message is closed and resumed in the next one. This matters because
the first dump message is allocated at NLMSG_GOODSIZE (a single page
on most architectures) regardless of the client's receive buffer;
packing every counter into one message would overflow it and fail
the dump with -EMSGSIZE. Userspace merges the attributes from every
message.

This allows nfsstat to retrieve server statistics via netlink
with a procfs fallback for older kernels.

Assisted-by: LLM
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260717-exportd-netlink-v7-3-b7ce17b83b60@kernel.org
Signed-off-by: Chuck Lever <cel@kernel.org>
This commit is contained in:
Jeff Layton 2026-07-17 07:08:55 -04:00 • committed by Chuck Lever
commit 36ed32f46e
5 changed files with 369 additions and 0 deletions
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