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

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Message-ID: <1669f62e-5ef5-8c7c-de01-540d96130cff@iogearbox.net>
Date:   Fri, 9 Nov 2018 10:10:17 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>,
        David Ahern <dsahern@...nel.org>
Cc:     netdev@...r.kernel.org, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH bpf-next] bpftool: Improve handling of ENOENT on map dumps

On 11/08/2018 10:25 PM, Jakub Kicinski wrote:
> On Thu,  8 Nov 2018 13:00:07 -0800, David Ahern wrote:
>> From: David Ahern <dsahern@...il.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@...il.com>
> 
> Seems good.  I wonder why "fd" maps report all indexes in get_next..
> 
> Acked-by: Jakub Kicinski <jakub.kicinski@...ronome.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>");
>> +			}
> 
> nit: in other places you don't add { }

Applied to bpf-next and fixed this nit up while doing so, thanks everyone!