bpf: btf: add pretty print for hash/lru_hash maps

Commit a26ca7c982cb ("bpf: btf: Add pretty print support to
the basic arraymap") added pretty print support to array map.
This patch adds pretty print for hash and lru_hash maps.
The following example shows the pretty-print result of
a pinned hashmap:

    struct map_value {
            int count_a;
            int count_b;
    };

    cat /sys/fs/bpf/pinned_hash_map:

    87907: {87907,87908}
    57354: {37354,57355}
    76625: {76625,76626}
    ...

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

1 files changed, 44 insertions, 0 deletions

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 513d9dfcf4ee..d6110042e0d9 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -11,9 +11,11 @@
  * General Public License for more details.
  */
 #include <linux/bpf.h>
+#include <linux/btf.h>
 #include <linux/jhash.h>
 #include <linux/filter.h>
 #include <linux/rculist_nulls.h>
+#include <uapi/linux/btf.h>
 #include "percpu_freelist.h"
 #include "bpf_lru_list.h"
 #include "map_in_map.h"
@@ -1162,6 +1164,44 @@ static void htab_map_free(struct bpf_map *map)
         kfree(htab);
 }
 
+static void htab_map_seq_show_elem(struct bpf_map *map, void *key,
+                                   struct seq_file *m)
+{
+        void *value;
+
+        rcu_read_lock();
+
+        value = htab_map_lookup_elem(map, key);
+        if (!value) {
+                rcu_read_unlock();
+                return;
+        }
+
+        btf_type_seq_show(map->btf, map->btf_key_type_id, key, m);
+        seq_puts(m, ": ");
+        btf_type_seq_show(map->btf, map->btf_value_type_id, value, m);
+        seq_puts(m, "\n");
+
+        rcu_read_unlock();
+}
+
+static int htab_map_check_btf(const struct bpf_map *map, const struct btf *btf,
+                              u32 btf_key_id, u32 btf_value_id)
+{
+        const struct btf_type *key_type, *value_type;
+        u32 key_size, value_size;
+
+        key_type = btf_type_id_size(btf, &btf_key_id, &key_size);
+        if (!key_type || key_size != map->key_size)
+                return -EINVAL;
+
+        value_type = btf_type_id_size(btf, &btf_value_id, &value_size);
+        if (!value_type || value_size != map->value_size)
+                return -EINVAL;
+
+        return 0;
+}
+
 const struct bpf_map_ops htab_map_ops = {
         .map_alloc_check = htab_map_alloc_check,
         .map_alloc = htab_map_alloc,
@@ -1171,6 +1211,8 @@ const struct bpf_map_ops htab_map_ops = {
         .map_update_elem = htab_map_update_elem,
         .map_delete_elem = htab_map_delete_elem,
         .map_gen_lookup = htab_map_gen_lookup,
+        .map_seq_show_elem = htab_map_seq_show_elem,
+        .map_check_btf = htab_map_check_btf,
 };
 
 const struct bpf_map_ops htab_lru_map_ops = {
@@ -1182,6 +1224,8 @@ const struct bpf_map_ops htab_lru_map_ops = {
         .map_update_elem = htab_lru_map_update_elem,
         .map_delete_elem = htab_lru_map_delete_elem,
         .map_gen_lookup = htab_lru_map_gen_lookup,
+        .map_seq_show_elem = htab_map_seq_show_elem,
+        .map_check_btf = htab_map_check_btf,
 };
 
 /* Called from eBPF program */