[PATCH bpf-next] bpftool: Improve handling of ENOENT on map dumps

[David Ahern <dsahern@kernel.org>]

From: David Ahern <dsahern@gmail.com>

bpftool output is not user friendly when dumping a map with only a few
populated entries:

    $ bpftool map
    1: devmap  name tx_devmap  flags 0x0
            key 4B  value 4B  max_entries 64  memlock 4096B
    2: array  name tx_idxmap  flags 0x0
            key 4B  value 4B  max_entries 64  memlock 4096B

    $ bpftool map dump id 1
    key:
    00 00 00 00
    value:
    No such file or directory
    key:
    01 00 00 00
    value:
    No such file or directory
    key:
    02 00 00 00
    value:
    No such file or directory
    key: 03 00 00 00  value: 03 00 00 00

Handle ENOENT by keeping the line format sane and dumping
"<no entry>" for the value

    $ bpftool map dump id 1
    key: 00 00 00 00  value: <no entry>
    key: 01 00 00 00  value: <no entry>
    key: 02 00 00 00  value: <no entry>
    key: 03 00 00 00  value: 03 00 00 00
    ...

Signed-off-by: David Ahern <dsahern@gmail.com>
---
Alternatively, could just omit the value, so:
key: 00 00 00 00  value:
key: 01 00 00 00  value:
key: 02 00 00 00  value:
key: 03 00 00 00  value: 03 00 00 00

 tools/bpf/bpftool/map.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index 101b8a881225..1f0060644e0c 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -383,7 +383,10 @@ static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
 		printf(single_line ? "  " : "\n");
 
 		printf("value:%c", break_names ? '\n' : ' ');
-		fprint_hex(stdout, value, info->value_size, " ");
+		if (value)
+			fprint_hex(stdout, value, info->value_size, " ");
+		else
+			printf("<no entry>");
 
 		printf("\n");
 	} else {
@@ -398,8 +401,12 @@ static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
 		for (i = 0; i < n; i++) {
 			printf("value (CPU %02d):%c",
 			       i, info->value_size > 16 ? '\n' : ' ');
-			fprint_hex(stdout, value + i * step,
-				   info->value_size, " ");
+			if (value) {
+				fprint_hex(stdout, value + i * step,
+					   info->value_size, " ");
+			} else {
+				printf("<no entry>");
+			}
 			printf("\n");
 		}
 	}
@@ -731,7 +738,11 @@ static int dump_map_elem(int fd, void *key, void *value,
 		jsonw_string_field(json_wtr, "error", strerror(lookup_errno));
 		jsonw_end_object(json_wtr);
 	} else {
-		print_entry_error(map_info, key, strerror(lookup_errno));
+		if (errno == ENOENT)
+			print_entry_plain(map_info, key, NULL);
+		else
+			print_entry_error(map_info, key,
+					  strerror(lookup_errno));
 	}
 
 	return 0;
-- 
2.11.0