"bpftool map dump" walks the map with bpf_map_get_next_key() and treats
ENOENT as the end of the map. Map types that can't be iterated fail that
call on the very first key: local storage and ringbuf with ENOTSUPP,
bloom filter and arena with EOPNOTSUPP, queue and stack with EINVAL.
bpftool then ends the walk without a word and prints what it prints for
an empty map, "[]" with BTF or "Found 0 elements" without, and only the
exit status tells that the map was not read. On a socket storage map
that holds storage for a socket:
# bpftool map dump pinned /sys/fs/bpf/sk_storage
[]
Ask for the first key before printing anything, and when that fails with
anything but ENOENT, fail with the map type and the error instead of a
dump:
# bpftool map dump pinned /sys/fs/bpf/sk_storage
Error: can't dump sk_storage map: Operation not supported
# bpftool -j map dump pinned /sys/fs/bpf/sk_storage
{"error":"can't dump sk_storage map: Operation not supported"}
An error later in the walk is now reported too, as "bpftool map getnext"
reports it, and the element count is printed only after a complete walk.
Assisted-by: LLM
Signed-off-by: Maxim Skokov <[email protected]>
Acked-by: Quentin Monnet <[email protected]>
---
tools/bpf/bpftool/map.c | 22 ++++++++++++++++++++--
1 file changed, 20 insertions(+), 2 deletions(-)
diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index d809b075e734f..4b65edf74859b 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -856,6 +856,21 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t
*wtr,
}
}
+ /* Fail early to avoid an empty dump if map type cannot be iterated */
+ if (bpf_map_get_next_key(fd, NULL, key) && errno != ENOENT) {
+ const char *map_type_str, *err_str;
+
+ err_str = bpf_strerror(errno);
+ map_type_str = libbpf_bpf_map_type_str(info->type);
+ if (map_type_str)
+ p_err("can't dump %s map: %s", map_type_str, err_str);
+ else
+ p_err("can't dump map of type %u: %s", info->type,
+ err_str);
+ err = -1;
+ goto exit_free;
+ }
+
if (wtr) {
err = get_map_kv_btf(info, &btf);
if (err) {
@@ -883,8 +898,11 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t
*wtr,
while (true) {
err = bpf_map_get_next_key(fd, prev_key, key);
if (err) {
- if (errno == ENOENT)
+ if (errno == ENOENT) {
err = 0;
+ break;
+ }
+ p_err("can't get next key: %s", bpf_strerror(errno));
break;
}
if (!dump_map_elem(fd, key, value, info, btf, wtr,
@@ -897,7 +915,7 @@ map_dump(int fd, struct bpf_map_info *info, json_writer_t
*wtr,
jsonw_end_array(wtr); /* elements */
if (show_header)
jsonw_end_object(wtr); /* map object */
- } else {
+ } else if (!err) {
printf("Found %u element%s\n", num_elems,
num_elems != 1 ? "s" : "");
}
--
2.47.3
