Re: [PATCH v4 1/3] io_uring: use an enumeration for io_uring_register(2) opcodes

From: Andreas Dilger <adilger@dilger.ca>
To: Kees Cook <keescook@chromium.org>
Cc: Stefano Garzarella <sgarzare@redhat.com>,
	Jens Axboe <axboe@kernel.dk>,
	Christian Brauner <christian.brauner@ubuntu.com>,
	Jann Horn <jannh@google.com>, Jeff Moyer <jmoyer@redhat.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Sargun Dhillon <sargun@sargun.me>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Kernel Hardening <kernel-hardening@lists.openwall.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Aleksa Sarai <asarai@suse.de>,
	io-uring@vger.kernel.org
Subject: Re: [PATCH v4 1/3] io_uring: use an enumeration for io_uring_register(2) opcodes
Date: Wed, 26 Aug 2020 13:52:38 -0600	[thread overview]
Message-ID: <C1F49852-C886-4522-ACD6-DDBF7DE3B838@dilger.ca> (raw)
In-Reply-To: <202008261241.074D8765@keescook>

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On Aug 26, 2020, at 1:43 PM, Kees Cook <keescook@chromium.org> wrote:
> 
> On Thu, Aug 13, 2020 at 05:32:52PM +0200, 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 d65fde732518..cdc98afbacc3 100644
>> --- a/include/uapi/linux/io_uring.h
>> +++ b/include/uapi/linux/io_uring.h
>> @@ -255,17 +255,22 @@ 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,
> 
> Actually, one *tiny* thought. Since this is UAPI, do we want to be extra
> careful here and explicitly assign values? We can't change the meaning
> of a number (UAPI) but we can add new ones, etc? This would help if an
> OP were removed (to stop from triggering a cascade of changed values)...
> 
> for example:
> 
> enum {
> 	IORING_REGISTER_BUFFERS = 0,
> 	IORING_UNREGISTER_BUFFERS = 1,
> 	...

Definitely that is preferred, IMHO, for enums used as part of UAPI,
as it avoids accidental changes to the values, and it also makes it
easier to see what the actual values are.

Cheers, Andreas

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