[PATCH v5 6/6] nfsd: export NFSv4 callback op stats via netlink

Add a proc4cb-ops nested attribute to the server-stats netlink dump,
reusing the existing server-proc-entry (op/count) layout. The first dump
message emits one entry per callback opcode (OP_CB_GETATTR..OP_CB_OFFLOAD)
from the per-netns callback counters; the set is small and fits alongside
the scalar stats, so no extra paging is needed.

This lets nfsstat report NFSv4 backchannel operation counts over netlink,
including CB_GETATTR which corresponds to the procfs wdeleg_getattr line.

Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Jeff Layton <[email protected]>
---
 Documentation/netlink/specs/nfsd.yaml |  6 ++++++
 fs/nfsd/nfsctl.c                      | 23 +++++++++++++++++++++++
 include/uapi/linux/nfsd_netlink.h     |  1 +
 3 files changed, 30 insertions(+)

diff --git a/Documentation/netlink/specs/nfsd.yaml b/Documentation/netlink/specs/nfsd.yaml
index 2a89d355ee7b..642268819c6f 100644
--- a/Documentation/netlink/specs/nfsd.yaml
+++ b/Documentation/netlink/specs/nfsd.yaml
@@ -410,6 +410,11 @@ attribute-sets:
         type: nest
         nested-attributes: server-proc-entry
         multi-attr: true
+      -
+        name: proc4cb-ops
+        type: nest
+        nested-attributes: server-proc-entry
+        multi-attr: true
 
 operations:
   list:
@@ -621,6 +626,7 @@ operations:
             - proc3-ops
             - proc4-ops
             - proc4ops-ops
+            - proc4cb-ops
 
 mcast-groups:
   list:
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 9bedbe7096c3..674fab6a86a5 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -2476,6 +2476,29 @@ int nfsd_nl_server_stats_get_dumpit(struct sk_buff *skb,
 			}
 		}
 
+#ifdef CONFIG_NFSD_V4
+		/* NFSv4 callback (backchannel) per-operation counts */
+		for (int op = OP_CB_GETATTR; op <= OP_CB_OFFLOAD; op++) {
+			struct nlattr *nest;
+			u64 cnt;
+
+			cnt = percpu_counter_sum_positive(
+				&nn->cb_counter[op]);
+
+			nest = nla_nest_start(skb,
+					NFSD_A_SERVER_STATS_PROC4CB_OPS);
+			if (!nest)
+				goto err_cancel;
+			if (nla_put_u32(skb, NFSD_A_SERVER_PROC_ENTRY_OP, op) ||
+			    nla_put_u64_64bit(skb, NFSD_A_SERVER_PROC_ENTRY_COUNT,
+					      cnt, NFSD_A_SERVER_PROC_ENTRY_PAD)) {
+				nla_nest_cancel(skb, nest);
+				goto err_cancel;
+			}
+			nla_nest_end(skb, nest);
+		}
+#endif
+
 		genlmsg_end(skb, hdr);
 		cb->args[0] = 1;
 	}
diff --git a/include/uapi/linux/nfsd_netlink.h b/include/uapi/linux/nfsd_netlink.h
index 3d076d173b1d..87da1d0bb21e 100644
--- a/include/uapi/linux/nfsd_netlink.h
+++ b/include/uapi/linux/nfsd_netlink.h
@@ -254,6 +254,7 @@ enum {
 	NFSD_A_SERVER_STATS_PROC3_OPS,
 	NFSD_A_SERVER_STATS_PROC4_OPS,
 	NFSD_A_SERVER_STATS_PROC4OPS_OPS,
+	NFSD_A_SERVER_STATS_PROC4CB_OPS,
 
 	__NFSD_A_SERVER_STATS_MAX,
 	NFSD_A_SERVER_STATS_MAX = (__NFSD_A_SERVER_STATS_MAX - 1)

-- 
2.54.0