nfsd: implement server-stats-get netlink handler

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>

1 files changed, 35 insertions, 0 deletions

diff --git a/include/uapi/linux/nfsd_netlink.h b/include/uapi/linux/nfsd_netlink.h
index f5b75d5caba9..3d076d173b1d 100644
--- a/include/uapi/linux/nfsd_netlink.h
+++ b/include/uapi/linux/nfsd_netlink.h
@@ -226,6 +226,40 @@ enum {
 };
 
 enum {
+	NFSD_A_SERVER_PROC_ENTRY_OP = 1,
+	NFSD_A_SERVER_PROC_ENTRY_COUNT,
+	NFSD_A_SERVER_PROC_ENTRY_PAD,
+
+	__NFSD_A_SERVER_PROC_ENTRY_MAX,
+	NFSD_A_SERVER_PROC_ENTRY_MAX = (__NFSD_A_SERVER_PROC_ENTRY_MAX - 1)
+};
+
+enum {
+	NFSD_A_SERVER_STATS_RC_HITS = 1,
+	NFSD_A_SERVER_STATS_RC_MISSES,
+	NFSD_A_SERVER_STATS_RC_NOCACHE,
+	NFSD_A_SERVER_STATS_PAD,
+	NFSD_A_SERVER_STATS_FH_STALE,
+	NFSD_A_SERVER_STATS_IO_READ,
+	NFSD_A_SERVER_STATS_IO_WRITE,
+	NFSD_A_SERVER_STATS_NETCNT,
+	NFSD_A_SERVER_STATS_NETUDPCNT,
+	NFSD_A_SERVER_STATS_NETTCPCNT,
+	NFSD_A_SERVER_STATS_NETTCPCONN,
+	NFSD_A_SERVER_STATS_RPCCNT,
+	NFSD_A_SERVER_STATS_RPCBADFMT,
+	NFSD_A_SERVER_STATS_RPCBADAUTH,
+	NFSD_A_SERVER_STATS_RPCBADCLNT,
+	NFSD_A_SERVER_STATS_PROC2_OPS,
+	NFSD_A_SERVER_STATS_PROC3_OPS,
+	NFSD_A_SERVER_STATS_PROC4_OPS,
+	NFSD_A_SERVER_STATS_PROC4OPS_OPS,
+
+	__NFSD_A_SERVER_STATS_MAX,
+	NFSD_A_SERVER_STATS_MAX = (__NFSD_A_SERVER_STATS_MAX - 1)
+};
+
+enum {
 	NFSD_CMD_RPC_STATUS_GET = 1,
 	NFSD_CMD_THREADS_SET,
 	NFSD_CMD_THREADS_GET,
@@ -244,6 +278,7 @@ enum {
 	NFSD_CMD_UNLOCK_IP,
 	NFSD_CMD_UNLOCK_FILESYSTEM,
 	NFSD_CMD_UNLOCK_EXPORT,
+	NFSD_CMD_SERVER_STATS_GET,
 
 	__NFSD_CMD_MAX,
 	NFSD_CMD_MAX = (__NFSD_CMD_MAX - 1)