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Date: Fri, 14 Nov 2014 07:33:00 -0800
Message-ID: <CAMEtUux2vuN3iNaAsxybyFwzfMRVe1+BOW-JvnvYYh+=-vpELw@mail.gmail.com>
Subject: Re: [PATCH v2 net-next 1/7] bpf: add 'flags' attribute to
 BPF_MAP_UPDATE_ELEM command
From: Alexei Starovoitov <ast@plumgrid.com>
To: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: "David S. Miller" <davem@davemloft.net>, Ingo Molnar <mingo@kernel.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Daniel Borkmann <dborkman@redhat.com>,
        Eric Dumazet <edumazet@google.com>,
        Linux API <linux-api@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Fri, Nov 14, 2014 at 4:11 AM, Hannes Frederic Sowa
<hannes@stressinduktion.org> wrote:
> On Do, 2014-11-13 at 17:36 -0800, Alexei Starovoitov wrote:
>> the current meaning of BPF_MAP_UPDATE_ELEM syscall command is:
>> either update existing map element or create a new one.
>> Initially the plan was to add a new command to handle the case of
>> 'create new element if it didn't exist', but 'flags' style looks
>> cleaner and overall diff is much smaller (more code reused), so add 'flags'
>> attribute to BPF_MAP_UPDATE_ELEM command with the following meaning:
>>  #define BPF_ANY      0 /* create new element or update existing */
>>  #define BPF_NOEXIST  1 /* create new element if it didn't exist */
>>  #define BPF_EXIST    2 /* update existing element */
>
> Would a cmpxchg-alike function be handy here?

you mean cmpxchg command in addition to
update() command ?
May be... it will have an extra 'value' argument
(key, old_value, new_value)
I don't have a use case for it yet though.
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