linux-kernel - Re: [PATCH RFC] io_uring: Pass whole sqe to commands

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Message-ID: <ZDVRGoDZo1tTbmZu@gmail.com>
Date:   Tue, 11 Apr 2023 05:22:50 -0700
From:   Breno Leitao <leitao@...ian.org>
To:     Keith Busch <kbusch@...nel.org>
Cc:     asml.silence@...il.com, axboe@...nel.dk, davem@...emloft.net,
        dccp@...r.kernel.org, dsahern@...nel.org, edumazet@...gle.com,
        io-uring@...r.kernel.org, kuba@...nel.org, leit@...com,
        linux-kernel@...r.kernel.org, marcelo.leitner@...il.com,
        matthieu.baerts@...sares.net, mptcp@...ts.linux.dev,
        netdev@...r.kernel.org, pabeni@...hat.com,
        willemdebruijn.kernel@...il.com
Subject: Re: [PATCH RFC] io_uring: Pass whole sqe to commands

On Fri, Apr 07, 2023 at 12:51:44PM -0600, Keith Busch wrote:
> > @@ -63,14 +63,15 @@ EXPORT_SYMBOL_GPL(io_uring_cmd_done);
> >  int io_uring_cmd_prep_async(struct io_kiocb *req)
> >  {
> >  	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
> > -	size_t cmd_size;
> > +	size_t size = sizeof(struct io_uring_sqe);
> >  
> >  	BUILD_BUG_ON(uring_cmd_pdu_size(0) != 16);
> >  	BUILD_BUG_ON(uring_cmd_pdu_size(1) != 80);
> 
> One minor suggestion. The above is the only user of uring_cmd_pdu_size() now,
> which is kind of a convoluted way to enfoce the offset of the 'cmd' field. It
> may be more clear to replace these with:

I agree with you here. Basically it is a bug if the payload (pdu) size is
is different than 16 for single SQE or != 80 for extended SQE.

So, basically it is checking for two things:
   * the cmd offset is 48
   * the io_uring_sqe struct is 64

Since this is a uapi, I am not confidence that they will change at all.
I can replace the code with your suggestion.

> 	BUILD_BUG_ON(offsetof(struct io_uring_sqe, cmd) == 48);

It should be "offset(struct io_uring_sqe, cmd) != 48)", right?

Thanks for the review!