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

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Date:   Fri, 12 Apr 2019 11:28:31 +0100
From:   Quentin Monnet <quentin.monnet@...ronome.com>
To:     Benjamin Poirier <bpoirier@...e.com>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     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

2019-04-12 12:03 UTC+0900 ~ Benjamin Poirier <bpoirier@...e.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@...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) {

Nit: This should be aligned on the open parenthesis (And preferably 
split after the "&&", if the second condition fits on its own line?).

Thanks for the changes! This version looks much better to me than v1.

Quentin