netdev - Re: [PATCH net-next] net: do not write to msg_get

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Message-ID: <c85d912d-8123-41dd-859d-255b4940b4cf@kernel.dk>
Date: Mon, 5 Jan 2026 10:34:26 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>, netdev@...r.kernel.org
Cc: davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
 pabeni@...hat.com, horms@...nel.org, kuniyu@...gle.com,
 Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] net: do not write to msg_get_inq in caller

On 1/5/26 9:32 AM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> msg_get_inq is an input field from caller to callee. Don't set it in
> the callee, as the caller may not clear it on struct reuse.
> 
> This is a kernel-internal variant of msghdr only, and the only user
> does reinitialize the field. So this is not critical.
> 
> But it is more robust to avoid the write, and slightly simpler code.
> 
> Callers set msg_get_inq to request the input queue length to be
> returned in msg_inq. This is equivalent to but independent from the
> SO_INQ request to return that same info as a cmsg (tp->recvmsg_inq).
> To reduce branching in the hot path the second also sets the msg_inq.
> That is WAI.
> 
> This is a small follow-on to commit 4d1442979e4a ("af_unix: don't
> post cmsg for SO_INQ unless explicitly asked for"), which fixed the
> inverse.
> 
> Also collapse two branches using a bitwise or.

Reviewed-by: Jens Axboe <axboe@...nel.dk>

I also ran my usual testing, and as expected, looks fine as well.

-- 
Jens Axboe