Re: [RFC v2 bpf-next 4/5] tools/bpf: bpftool, print strerror when map lookup error occurs

[Jakub Kicinski]

On Tue,  2 Oct 2018 14:35:18 +0900, Prashant Bhole wrote:
> Since map lookup error can be ENOENT or EOPNOTSUPP, let's print
> strerror() as error message in normal and JSON output.
> 
> This patch adds helper function print_entry_error() to print
> entry from lookup error occurs
> 
> Example: Following example dumps a map which does not support lookup.
> 
...

Acked-by: Jakub Kicinski 

Thank you!

[RFC v2 bpf-next 4/5] tools/bpf: bpftool, print strerror when map lookup error occurs

[Prashant Bhole]

Since map lookup error can be ENOENT or EOPNOTSUPP, let's print
strerror() as error message in normal and JSON output.

This patch adds helper function print_entry_error() to print
entry from lookup error occurs

Example: Following example dumps a map which does not support lookup.

Output before:
root# bpftool map -jp dump id 40
[
"key": ["0x0a","0x00","0x00","0x00"
],
"value": {
"error": "can\'t lookup element"
},
"key": ["0x0b","0x00","0x00","0x00"
],
"value": {
"error": "can\'t lookup element"
}
]

root# bpftool map dump id 40
can't lookup element with key:
0a 00 00 00
can't lookup element with key:
0b 00 00 00
Found 0 elements

Output after changes:
root# bpftool map dump -jp  id 45
[
"key": ["0x0a","0x00","0x00","0x00"
],
"value": {
"error": "Operation not supported"
},
"key": ["0x0b","0x00","0x00","0x00"
],
"value": {
"error": "Operation not supported"
}
]

root# bpftool map dump id 45
key:
0a 00 00 00
value:
Operation not supported
key:
0b 00 00 00
value:
Operation not supported
Found 0 elements

Signed-off-by: Prashant Bhole 
---
 tools/bpf/bpftool/map.c | 29 -
 1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index 28d365435fea..9f5de48f8a99 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -336,6 +336,25 @@ static void print_entry_json(struct bpf_map_info *info, 
unsigned char *key,
jsonw_end_object(json_wtr);
 }
 
+static void print_entry_error(struct bpf_map_info *info, unsigned char *key,
+ const char *value)
+{
+   int value_size = strlen(value);
+   bool single_line, break_names;
+
+   break_names = info->key_size > 16 || value_size > 16;
+   single_line = info->key_size + value_size <= 24 && !break_names;
+
+   printf("key:%c", break_names ? '\n' : ' ');
+   fprint_hex(stdout, key, info->key_size, " ");
+
+   printf(single_line ? "  " : "\n");
+
+   printf("value:%c%s", break_names ? '\n' : ' ', value);
+
+   printf("\n");
+}
+
 static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
  unsigned char *value)
 {
@@ -663,6 +682,7 @@ static int dump_map_elem(int fd, void *key, void *value,
 json_writer_t *btf_wtr)
 {
int num_elems = 0;
+   int lookup_errno;
 
if (!bpf_map_lookup_elem(fd, key, value)) {
if (json_output) {
@@ -685,6 +705,8 @@ static int dump_map_elem(int fd, void *key, void *value,
}
 
/* lookup error handling */
+   lookup_errno = errno;
+
if (map_is_map_of_maps(map_info->type) ||
map_is_map_of_progs(map_info->type))
return 0;
@@ -694,13 +716,10 @@ static int dump_map_elem(int fd, void *key, void *value,
print_hex_data_json(key, map_info->key_size);
jsonw_name(json_wtr, "value");
jsonw_start_object(json_wtr);
-   jsonw_string_field(json_wtr, "error",
-  "can't lookup element");
+   jsonw_string_field(json_wtr, "error", strerror(lookup_errno));
jsonw_end_object(json_wtr);
} else {
-   p_info("can't lookup element with key: ");
-   fprint_hex(stderr, key, map_info->key_size, " ");
-   fprintf(stderr, "\n");
+   print_entry_error(map_info, key, strerror(lookup_errno));
}
 
return 0;
-- 
2.17.1