net: page_pool: expose page pool stats via netlink

Dump the stats into netlink. More clever approaches
like dumping the stats per-CPU for each CPU individually
to see where the packets get consumed can be implemented
in the future.

A trimmed example from a real (but recently booted system):

$ ./cli.py --no-schema --spec netlink/specs/netdev.yaml \
           --dump page-pool-stats-get
[{'info': {'id': 19, 'ifindex': 2},
  'alloc-empty': 48,
  'alloc-fast': 3024,
  'alloc-refill': 0,
  'alloc-slow': 48,
  'alloc-slow-high-order': 0,
  'alloc-waive': 0,
  'recycle-cache-full': 0,
  'recycle-cached': 0,
  'recycle-released-refcnt': 0,
  'recycle-ring': 0,
  'recycle-ring-full': 0},
 {'info': {'id': 18, 'ifindex': 2},
  'alloc-empty': 66,
  'alloc-fast': 11811,
  'alloc-refill': 35,
  'alloc-slow': 66,
  'alloc-slow-high-order': 0,
  'alloc-waive': 0,
  'recycle-cache-full': 1145,
  'recycle-cached': 6541,
  'recycle-released-refcnt': 0,
  'recycle-ring': 1275,
  'recycle-ring-full': 0},
 {'info': {'id': 17, 'ifindex': 2},
  'alloc-empty': 73,
  'alloc-fast': 62099,
  'alloc-refill': 413,
...

Acked-by: Jesper Dangaard Brouer <hawk@kernel.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Documentation/netlink/specs/netdev.yaml

@@ -139,6 +139,59 @@ attribute-sets:
           "re-attached", they are just waiting to disappear.
           Attribute is absent if Page Pool has not been detached, and
           can still be used to allocate new memory.
+  -
+    name: page-pool-info
+    subset-of: page-pool
+    attributes:
+      -
+        name: id
+      -
+        name: ifindex
+  -
+    name: page-pool-stats
+    doc: |
+      Page pool statistics, see docs for struct page_pool_stats
+      for information about individual statistics.
+    attributes:
+      -
+        name: info
+        doc: Page pool identifying information.
+        type: nest
+        nested-attributes: page-pool-info
+      -
+        name: alloc-fast
+        type: uint
+        value: 8 # reserve some attr ids in case we need more metadata later
+      -
+        name: alloc-slow
+        type: uint
+      -
+        name: alloc-slow-high-order
+        type: uint
+      -
+        name: alloc-empty
+        type: uint
+      -
+        name: alloc-refill
+        type: uint
+      -
+        name: alloc-waive
+        type: uint
+      -
+        name: recycle-cached
+        type: uint
+      -
+        name: recycle-cache-full
+        type: uint
+      -
+        name: recycle-ring
+        type: uint
+      -
+        name: recycle-ring-full
+        type: uint
+      -
+        name: recycle-released-refcnt
+        type: uint
 
 operations:
   list:
@@ -212,6 +265,31 @@ operations:
       notify: page-pool-get
       mcgrp: page-pool
       config-cond: page-pool
+    -
+      name: page-pool-stats-get
+      doc: Get page pool statistics.
+      attribute-set: page-pool-stats
+      do:
+        request:
+          attributes:
+            - info
+        reply: &pp-stats-reply
+          attributes:
+            - info
+            - alloc-fast
+            - alloc-slow
+            - alloc-slow-high-order
+            - alloc-empty
+            - alloc-refill
+            - alloc-waive
+            - recycle-cached
+            - recycle-cache-full
+            - recycle-ring
+            - recycle-ring-full
+            - recycle-released-refcnt
+      dump:
+        reply: *pp-stats-reply
+      config-cond: page-pool-stats
 
 mcast-groups:
   list: