linux-kernel - Re: [PATCH RFC v2 1/3] io_uring: use an enumeration for io_uring

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Message-ID: <20200717081333.6z6rtwx3jtktwdvp@steredhat.lan>
Date:   Fri, 17 Jul 2020 10:13:33 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Pavel Begunkov <asml.silence@...il.com>,
        Jens Axboe <axboe@...nel.dk>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Kees Cook <keescook@...omium.org>,
        Aleksa Sarai <asarai@...e.de>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Sargun Dhillon <sargun@...gun.me>,
        Jann Horn <jannh@...gle.com>, io-uring@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jeff Moyer <jmoyer@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 1/3] io_uring: use an enumeration for
 io_uring_register(2) opcodes

On Thu, Jul 16, 2020 at 03:20:53PM -0600, Jens Axboe wrote:
> On 7/16/20 2:51 PM, Jens Axboe wrote:
> > On 7/16/20 2:47 PM, Pavel Begunkov wrote:
> >> On 16/07/2020 23:42, Jens Axboe wrote:
> >>> On 7/16/20 2:16 PM, Pavel Begunkov wrote:
> >>>> On 16/07/2020 15:48, Stefano Garzarella wrote:
> >>>>> The enumeration allows us to keep track of the last
> >>>>> io_uring_register(2) opcode available.
> >>>>>
> >>>>> Behaviour and opcodes names don't change.
> >>>>>
> >>>>> Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
> >>>>> ---
> >>>>>  include/uapi/linux/io_uring.h | 27 ++++++++++++++++-----------
> >>>>>  1 file changed, 16 insertions(+), 11 deletions(-)
> >>>>>
> >>>>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
> >>>>> index 7843742b8b74..efc50bd0af34 100644
> >>>>> --- a/include/uapi/linux/io_uring.h
> >>>>> +++ b/include/uapi/linux/io_uring.h
> >>>>> @@ -253,17 +253,22 @@ struct io_uring_params {
> >>>>>  /*
> >>>>>   * io_uring_register(2) opcodes and arguments
> >>>>>   */
> >>>>> -#define IORING_REGISTER_BUFFERS		0
> >>>>> -#define IORING_UNREGISTER_BUFFERS	1
> >>>>> -#define IORING_REGISTER_FILES		2
> >>>>> -#define IORING_UNREGISTER_FILES		3
> >>>>> -#define IORING_REGISTER_EVENTFD		4
> >>>>> -#define IORING_UNREGISTER_EVENTFD	5
> >>>>> -#define IORING_REGISTER_FILES_UPDATE	6
> >>>>> -#define IORING_REGISTER_EVENTFD_ASYNC	7
> >>>>> -#define IORING_REGISTER_PROBE		8
> >>>>> -#define IORING_REGISTER_PERSONALITY	9
> >>>>> -#define IORING_UNREGISTER_PERSONALITY	10
> >>>>> +enum {
> >>>>> +	IORING_REGISTER_BUFFERS,
> >>>>> +	IORING_UNREGISTER_BUFFERS,
> >>>>> +	IORING_REGISTER_FILES,
> >>>>> +	IORING_UNREGISTER_FILES,
> >>>>> +	IORING_REGISTER_EVENTFD,
> >>>>> +	IORING_UNREGISTER_EVENTFD,
> >>>>> +	IORING_REGISTER_FILES_UPDATE,
> >>>>> +	IORING_REGISTER_EVENTFD_ASYNC,
> >>>>> +	IORING_REGISTER_PROBE,
> >>>>> +	IORING_REGISTER_PERSONALITY,
> >>>>> +	IORING_UNREGISTER_PERSONALITY,
> >>>>> +
> >>>>> +	/* this goes last */
> >>>>> +	IORING_REGISTER_LAST
> >>>>> +};
> >>>>
> >>>> It breaks userspace API. E.g.
> >>>>
> >>>> #ifdef IORING_REGISTER_BUFFERS
> >>>
> >>> It can, yes, but we have done that in the past. In this one, for
> >>
> >> Ok, if nobody on the userspace side cares, then better to do that
> >> sooner than later.
> 
> I actually don't think it's a huge issue. Normally if applications
> do this, it's because they are using it and need it. Ala:
> 
> #ifndef IORING_REGISTER_SOMETHING
> #define IORING_REGISTER_SOMETHING	fooval
> #endif
> 
> and that'll still work just fine, even if an identical enum is there.
> 

Thank you both for the review!

Then if you agree, I'll leave this patch as it is by introducing the enum.

Stefano