netdev - Re: [PATCH v2 bpf-next 2/2] bpftool: Improve handling of ENOSPC on reuseport

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Date:   Fri, 12 Apr 2019 17:00:33 -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 v2 bpf-next 2/2] bpftool: Improve handling of ENOSPC on
 reuseport_array map dumps

On Fri, 12 Apr 2019 12:03:22 +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@...e.com>
> ---
>  tools/bpf/bpftool/map.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
> index 71840faaeab5..e6d72f777767 100644
> --- a/tools/bpf/bpftool/map.c
> +++ b/tools/bpf/bpftool/map.c
> @@ -716,8 +716,12 @@ static int dump_map_elem(int fd, void *key, void *value,
>  	} else {
>  		const char *msg = NULL;
>  
> -		if (errno == ENOENT)
> +		if (lookup_errno == ENOENT) {
>  			msg = "<no entry>";
> +		} else if (lookup_errno == ENOSPC && map_info->type ==
> +			 BPF_MAP_TYPE_REUSEPORT_SOCKARRAY) {
> +			msg = "<cannot read>";
> +		}

In addition to Quentin's nit please don't use the curly brackets for
single-line statements.

>  		print_entry_error(map_info, key,
>  				  msg ? : strerror(lookup_errno), !!msg);
> @@ -774,6 +778,11 @@ 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]);
> +	}

Same here :)

>  	while (true) {
>  		err = bpf_map_get_next_key(fd, prev_key, key);
>  		if (err) {