netdev - [PATCH bpf-next v3 2/3] tools: bpftool: keep errors for map-of-map dumps if distinct from ENOENT

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Date:   Thu, 10 Sep 2020 11:26:51 +0100
From:   Quentin Monnet <quentin@...valent.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Quentin Monnet <quentin@...valent.com>
Subject: [PATCH bpf-next v3 2/3] tools: bpftool: keep errors for map-of-map dumps if distinct from ENOENT

When dumping outer maps or prog_array maps, and on lookup failure,
bpftool simply skips the entry with no error message. This is because
the kernel returns non-zero when no value is found for the provided key,
which frequently happen for those maps if they have not been filled.

When such a case occurs, errno is set to ENOENT. It seems unlikely we
could receive other error codes at this stage (we successfully retrieved
map info just before), but to be on the safe side, let's skip the entry
only if errno was ENOENT, and not for the other errors.

v3: New patch

Signed-off-by: Quentin Monnet <quentin@...valent.com>
---
 tools/bpf/bpftool/map.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index c8159cb4fb1e..d8581d5e98a1 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -240,8 +240,8 @@ print_entry_error(struct bpf_map_info *map_info, void *key, int lookup_errno)
 	 * means there is no entry for that key. Do not print an error message
 	 * in that case.
 	 */
-	if (map_is_map_of_maps(map_info->type) ||
-	    map_is_map_of_progs(map_info->type))
+	if ((map_is_map_of_maps(map_info->type) ||
+	     map_is_map_of_progs(map_info->type)) && lookup_errno == ENOENT)
 		return;

 	if (json_output) {
-- 
2.25.1