[RFC bpf-next 1/3] tools: bpftool: clean up dump_map_elem() return value

[Quentin Monnet <quentin.monnet@netronome.com>]

The code for dumping a map entry (as part of a full map dump) was moved
to a specific function dump_map_elem() in commit 18a781daa93e
("tools/bpf: bpftool, split the function do_dump()"). The "num_elems"
variable was moved in that function, incremented on success, and
returned to be immediately added to the counter in do_dump().

Returning the count of elements dumped, which is either 0 or 1, is not
really consistent with the rest of the function, especially because
"dump_map_elem()" name is not explicit about returning a counter.
Furthermore, the counter is not incremented when the entry is dumped in
JSON. This has no visible effect, because the number of elements
successfully dumped is not printed for JSON output.

Still, let's remove "num_elems" from the function and make it return 0
or -1 in case of success or failure, respectively. This is more correct,
and more consistent with the rest of the code.

It is unclear if an error value should indeed be returned for maps of
maps or maps of progs, but this has no effect on the output either, so
we just leave the current behaviour unchanged.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
---
 tools/bpf/bpftool/map.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index bfbbc6b4cb83..206ee46189d9 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -686,7 +686,6 @@ static int dump_map_elem(int fd, void *key, void *value,
 			 struct bpf_map_info *map_info, struct btf *btf,
 			 json_writer_t *btf_wtr)
 {
-	int num_elems = 0;
 	int lookup_errno;
 
 	if (!bpf_map_lookup_elem(fd, key, value)) {
@@ -704,9 +703,8 @@ static int dump_map_elem(int fd, void *key, void *value,
 			} else {
 				print_entry_plain(map_info, key, value);
 			}
-			num_elems++;
 		}
-		return num_elems;
+		return 0;
 	}
 
 	/* lookup error handling */
@@ -714,7 +712,7 @@ static int dump_map_elem(int fd, void *key, void *value,
 
 	if (map_is_map_of_maps(map_info->type) ||
 	    map_is_map_of_progs(map_info->type))
-		return 0;
+		return -1;
 
 	if (json_output) {
 		jsonw_start_object(json_wtr);
@@ -738,7 +736,7 @@ static int dump_map_elem(int fd, void *key, void *value,
 				  msg ? : strerror(lookup_errno));
 	}
 
-	return 0;
+	return -1;
 }
 
 static int do_dump(int argc, char **argv)
@@ -800,7 +798,8 @@ static int do_dump(int argc, char **argv)
 				err = 0;
 			break;
 		}
-		num_elems += dump_map_elem(fd, key, value, &info, btf, btf_wtr);
+		if (!dump_map_elem(fd, key, value, &info, btf, btf_wtr))
+			num_elems++;
 		prev_key = key;
 	}
 
-- 
2.17.1