Merge branch 'bpf-btf-for-htab-lru'

Yonghong Song says:

====================
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. Without this patch set, user will get an error instead.

    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}
    ...

Patch #1 fixed a bug in bpffs map_seq_next() function so that
all elements in the hash table will be traversed.
Patch #2 implemented map_seq_show_elem() and map_check_btf()
callback functions for hash and lru hash maps.
Patch #3 enhanced tools/testing/selftests/bpf/test_btf.c to
test bpffs hash and lru hash map pretty print.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

2 files changed, 49 insertions, 3 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 */
diff --git a/kernel/bpf/inode.c b/kernel/bpf/inode.c
index 76efe9a183f5..fc5b103512e7 100644
--- a/kernel/bpf/inode.c
+++ b/kernel/bpf/inode.c
@@ -196,19 +196,21 @@ static void *map_seq_next(struct seq_file *m, void *v, loff_t *pos)
 {
 	struct bpf_map *map = seq_file_to_map(m);
 	void *key = map_iter(m)->key;
+	void *prev_key;
 
 	if (map_iter(m)->done)
 		return NULL;
 
 	if (unlikely(v == SEQ_START_TOKEN))
-		goto done;
+		prev_key = NULL;
+	else
+		prev_key = key;
 
-	if (map->ops->map_get_next_key(map, key, key)) {
+	if (map->ops->map_get_next_key(map, prev_key, key)) {
 		map_iter(m)->done = true;
 		return NULL;
 	}
 
-done:
 	++(*pos);
 	return key;
 }