netdev - Re: [PATCH net] tcp: Export tcp_write_queue

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Date:   Thu, 30 Jul 2020 14:23:50 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     netdev <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] tcp: Export tcp_write_queue_purge()

On 7/30/20 2:16 PM, Eric Dumazet wrote:
> On Thu, Jul 30, 2020 at 2:07 PM Florian Fainelli <f.fainelli@...il.com> wrote:
>>
>> After tcp_write_queue_purge() got uninlined with commit ac3f09ba3e49
>> ("tcp: uninline tcp_write_queue_purge()"), it became no longer possible
>> to reference this symbol from kernel modules.
>>
>> Fixes: ac3f09ba3e49 ("tcp: uninline tcp_write_queue_purge()")
>> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
>> ---
>>  net/ipv4/tcp.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
>> index 6f0caf9a866d..ea9d296a8380 100644
>> --- a/net/ipv4/tcp.c
>> +++ b/net/ipv4/tcp.c
>> @@ -2626,6 +2626,7 @@ void tcp_write_queue_purge(struct sock *sk)
>>         tcp_sk(sk)->packets_out = 0;
>>         inet_csk(sk)->icsk_backoff = 0;
>>  }
>> +EXPORT_SYMBOL(tcp_write_queue_purge);
>>
>>  int tcp_disconnect(struct sock *sk, int flags)
>>  {
>> --
>> 2.17.1
>>
> 
> Hmmm.... which module would need this exactly ?

None in tree unfortunately, and I doubt it would be published one day.
For consistency one could argue that given it used to be accessible, and
other symbols within net/ipv4/tcp.c are also exported, so this should
one be. Not going to hold that line of argumentation more than in this
email, if you object to it, that would be completely fine with me.

> 
> How come it took 3 years to discover this issue ?

We just upgraded our downstream kernel from 4.9 to 5.4 and this is why
it took so long.
-- 
Florian