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

[Stefano Garzarella <sgarzare@redhat.com>]

On Wed, Aug 26, 2020 at 01:52:38PM -0600, Andreas Dilger wrote:
> 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.
> 

Sure, I agree.

I'll put the values in the enumerations in the v5.

Thanks,
Stefano