[v3,bpf-next,2/2] bpftool: Improve handling of ENOSPC on reuseport_array map dumps

avoids outputting a series of
	value:
	No space left on device

The value itself is not wrong but bpf_fd_reuseport_array_lookup_elem() can
only return it if the map was created with value_size = 8. There's nothing
bpftool can do about it. Instead of repeating this error for every key in
the map, print an explanatory warning and a specialized error.

example before:
key: 00 00 00 00
value:
No space left on device
key: 01 00 00 00
value:
No space left on device
key: 02 00 00 00
value:
No space left on device
Found 0 elements

example after:
Warning: cannot read values from reuseport_sockarray map with value_size != 8
key: 00 00 00 00  value: <cannot read>
key: 01 00 00 00  value: <cannot read>
key: 02 00 00 00  value: <cannot read>
Found 0 elements

Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
---
 tools/bpf/bpftool/map.c | 7 +++++++
 1 file changed, 7 insertions(+)

2019-04-15 16:15 UTC+0900 ~ Benjamin Poirier <bpoirier@suse.com>
> avoids outputting a series of
> 	value:
> 	No space left on device
> 
> The value itself is not wrong but bpf_fd_reuseport_array_lookup_elem() can
> only return it if the map was created with value_size = 8. There's nothing
> bpftool can do about it. Instead of repeating this error for every key in
> the map, print an explanatory warning and a specialized error.
> 
> example before:
> key: 00 00 00 00
> value:
> No space left on device
> key: 01 00 00 00
> value:
> No space left on device
> key: 02 00 00 00
> value:
> No space left on device
> Found 0 elements
> 
> example after:
> Warning: cannot read values from reuseport_sockarray map with value_size != 8
> key: 00 00 00 00  value: <cannot read>
> key: 01 00 00 00  value: <cannot read>
> key: 02 00 00 00  value: <cannot read>
> Found 0 elements
> 
> Signed-off-by: Benjamin Poirier <bpoirier@suse.com>
> ---
>   tools/bpf/bpftool/map.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index df958af56b6c..44b192e87708 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -719,6 +719,9 @@ static int dump_map_elem(int fd, void *key, void *value,
>   
>   		if (errno == ENOENT)
>   			msg = "<no entry>";
> +		else if (lookup_errno == ENOSPC &&
> +			 map_info->type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY)
> +			msg = "<cannot read>";
>   
>   		print_entry_error(map_info, key,
>   				  msg ? : strerror(lookup_errno));
> @@ -775,6 +778,10 @@ static int do_dump(int argc, char **argv)
>   			}
>   		}
>   
> +	if (info.type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY &&
> +	    info.value_size != 8)
> +		p_info("Warning: cannot read values from %s map with value_size != 8",
> +		       map_type_name[info.type]);
>   	while (true) {
>   		err = bpf_map_get_next_key(fd, prev_key, key);
>   		if (err) {
> 

All good for me now, thanks a lot!

Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>

On Mon, 15 Apr 2019 16:15:36 +0900, Benjamin Poirier wrote:
> avoids outputting a series of
> 	value:
> 	No space left on device
> 
> The value itself is not wrong but bpf_fd_reuseport_array_lookup_elem() can
> only return it if the map was created with value_size = 8. There's nothing
> bpftool can do about it. Instead of repeating this error for every key in
> the map, print an explanatory warning and a specialized error.
> 
> example before:
> key: 00 00 00 00
> value:
> No space left on device
> key: 01 00 00 00
> value:
> No space left on device
> key: 02 00 00 00
> value:
> No space left on device
> Found 0 elements
> 
> example after:
> Warning: cannot read values from reuseport_sockarray map with value_size != 8
> key: 00 00 00 00  value: <cannot read>
> key: 01 00 00 00  value: <cannot read>
> key: 02 00 00 00  value: <cannot read>
> Found 0 elements
> 
> Signed-off-by: Benjamin Poirier <bpoirier@suse.com>

Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>

Thank you!!