netdev - Re: [PATCH bpf-next] bpftool: Exit early when it's not possible to dump a REUSEPORT

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Date:   Thu, 11 Apr 2019 13:31:51 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Benjamin Poirier <bpoirier@...e.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpftool: Exit early when it's not possible to
 dump a REUSEPORT_SOCKARRAY map

On Thu, 11 Apr 2019 17:27:00 +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 the error once, print an explanatory message and exit.
> 
> Signed-off-by: Benjamin Poirier <bpoirier@...e.com>

> @@ -787,7 +787,16 @@ static int do_dump(int argc, char **argv)
>  				err = 0;
>  			break;
>  		}
> -		num_elems += dump_map_elem(fd, key, value, &info, btf, btf_wtr);
> +		err = dump_map_elem(fd, key, value, &info, btf, btf_wtr);
> +		/* bpf_fd_reuseport_array_lookup_elem() can only return a
> +		 * value if the map's value_size == 8
> +		 */
> +		if (info.type == BPF_MAP_TYPE_REUSEPORT_SOCKARRAY &&
> +		    info.value_size != 8 && err == -ENOSPC) {
> +			p_err("cannot dump REUSEPORT_SOCKARRAY map with value_size != 8");
> +			goto exit_free;

Hmm... could it still be useful to walk the map to see the keys, even
if the kernel can't return meaningful values?

> +		}
> +		num_elems += err;
>  		prev_key = key;
>  	}
>