netdev - Re: [PATCH bpf] bpf: fix bpffs non-array map seq

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Date:   Wed, 8 Aug 2018 19:25:31 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Yonghong Song <yhs@...com>
Cc:     ast@...com, daniel@...earbox.net, netdev@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH bpf] bpf: fix bpffs non-array map seq_show issue

On Wed, Aug 08, 2018 at 06:25:19PM -0700, Yonghong Song wrote:
> In function map_seq_next() of kernel/bpf/inode.c,
> the first key will be the "0" regardless of the map type.
> This works for array. But for hash type, if it happens
> key "0" is in the map, the bpffs map show will miss
> some items if the key "0" is not the first element of
> the first bucket.
> 
> This patch fixed the issue by guaranteeing to get
> the first element, if the seq_show is just started,
> by passing NULL pointer key to map_get_next_key() callback.
> This way, no missing elements will occur for
> bpffs hash table show even if key "0" is in the map.
> 
> Fixes: a26ca7c982cb5 ("bpf: btf: Add pretty print support to the basic arraymap")
> Signed-off-by: Yonghong Song <yhs@...com>

Acked-by: Alexei Starovoitov <ast@...nel.org>