netdev - Re: [PATCH v2 net 01/15] af_unix: Set sk->sk_state under unix_state

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Message-ID: <c550e27c-6a45-4219-98d8-f6d237c0674e@rbox.co>
Date: Wed, 26 Jun 2024 12:48:27 +0200
From: Michal Luczaj <mhal@...x.co>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: cong.wang@...edance.com, davem@...emloft.net, edumazet@...gle.com,
 kuba@...nel.org, kuni1840@...il.com, netdev@...r.kernel.org,
 pabeni@...hat.com
Subject: Re: [PATCH v2 net 01/15] af_unix: Set sk->sk_state under
 unix_state_lock() for truly disconencted peer.

On 6/23/24 07:19, Kuniyuki Iwashima wrote:
> From: Michal Luczaj <mhal@...x.co>
> Date: Sun, 23 Jun 2024 00:43:27 +0200
>> I gotta ask, is there a reason for unlinking an already consumed
>> ('consumed' as in 'unix_skb_len(skb) == 0') skb so late, in manage_oob()?
>> IOW, can't it be unlinked immediately once it's consumed in
>> unix_stream_recv_urg()? I suppose that would simplify things.
> 
> I also thought that before, but we can't do that.
> 
> Even after reading OOB data, we need to remember the position
> and break recv() at that point.  That's why the skb is unlinked
> in manage_oob() rather than unix_stream_recv_urg().

Ahh, I see. Thanks for explaining.

One more thing about unix sockmap. AF_UNIX SOCK_DGRAM supports 0-length
packets. But sockmap doesn't handle that; once a 0-length skb/msg is in the
psock queue, unix_bpf_recvmsg() starts throwing -EFAULT. Sockmap'ed AF_INET
SOCK_DGRAM does the same, so is this a bug or a feature?