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

[David Ahern]

From: David Ahern <dsah...@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 <dsah...@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