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Subject: Re: [PATCH RFC v2 1/3] io_uring: use an enumeration for
 io_uring_register(2) opcodes
To:     Pavel Begunkov <asml.silence@gmail.com>,
        Stefano Garzarella <sgarzare@redhat.com>
Cc:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        Kees Cook <keescook@chromium.org>,
        Aleksa Sarai <asarai@suse.de>,
        Stefan Hajnoczi <stefanha@redhat.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Sargun Dhillon <sargun@sargun.me>,
        Jann Horn <jannh@google.com>, io-uring@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, Jeff Moyer <jmoyer@redhat.com>,
        linux-kernel@vger.kernel.org
References: <20200716124833.93667-1-sgarzare@redhat.com>
 <20200716124833.93667-2-sgarzare@redhat.com>
 <ca242a15-576d-4099-a5f8-85c08985e3ff@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <a2f109b2-adbf-147d-9423-7a1a4bf99967@kernel.dk>
Date:   Thu, 16 Jul 2020 14:42:08 -0600
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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@redhat.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
example:

commit 9e3aa61ae3e01ce1ce6361a41ef725e1f4d1d2bf (tag: io_uring-5.5-20191212)
Author: Jens Axboe <axboe@kernel.dk>
Date:   Wed Dec 11 15:55:43 2019 -0700

    io_uring: ensure we return -EINVAL on unknown opcod

But it would be safer/saner to do this like we have the done the IOSQE_
flags.

-- 
Jens Axboe