[PATCH bpf-next 5/7] bpf: add new map ops ->map_mem_usage

[Yafang Shao <laoar.shao@xxxxxxxxx>]

Add a new map ops ->map_mem_usage to print the memory usage of a
bpf map.

->map_mem_usage will get the map memory usage from the pointers
which will be freed in ->map_free. So it is very similar to ->map_free
except that it only get the underlaying memory size from the pointers
rather than freeing them. We just need to keep the pointers used in
->map_mem_usage in sync with the pointers in ->map_free.

This is a preparation for the followup change.

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 include/linux/bpf.h  |  2 ++
 kernel/bpf/syscall.c | 18 +++++++++++-------
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index e11db75..10eb8e9 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -160,6 +160,8 @@ struct bpf_map_ops {
 				     bpf_callback_t callback_fn,
 				     void *callback_ctx, u64 flags);
 
+	unsigned long (*map_mem_usage)(const struct bpf_map *map);
+
 	/* BTF id of struct allocated by map_alloc */
 	int *map_btf_id;
 
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 99417b3..df52853 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -758,16 +758,20 @@ static fmode_t map_get_sys_perms(struct bpf_map *map, struct fd f)
 }
 
 #ifdef CONFIG_PROC_FS
-/* Provides an approximation of the map's memory footprint.
- * Used only to provide a backward compatibility and display
- * a reasonable "memlock" info.
- */
-static unsigned long bpf_map_memory_footprint(const struct bpf_map *map)
+/* Show the memory usage of a bpf map */
+static unsigned long bpf_map_memory_usage(const struct bpf_map *map)
 {
 	unsigned long size;
 
-	size = round_up(map->key_size + bpf_map_value_size(map), 8);
+	/* ->map_mem_usage will get the map memory size from the pointers
+	 * which will be freed in ->map_free. So it is very similar to
+	 * ->map_free except that it only get the underlaying memory size
+	 * from the pointers rather than freeing them.
+	 */
+	if (map->ops->map_mem_usage)
+		return map->ops->map_mem_usage(map);
 
+	size = round_up(map->key_size + bpf_map_value_size(map), 8);
 	return round_up(map->max_entries * size, PAGE_SIZE);
 }
 
@@ -799,7 +803,7 @@ static void bpf_map_show_fdinfo(struct seq_file *m, struct file *filp)
 		   map->max_entries,
 		   map->map_flags,
 		   (unsigned long long)map->map_extra,
-		   bpf_map_memory_footprint(map),
+		   bpf_map_memory_usage(map),
 		   map->id,
 		   READ_ONCE(map->frozen));
 	if (type) {
-- 
1.8.3.1