Re: [PATCH 2/9] io_uring: support user sqe ext flags

[Ming Lei <ming.lei@redhat.com>]

On Mon, Apr 22, 2024 at 12:16:12PM -0600, Jens Axboe wrote:
> On 4/7/24 7:03 PM, Ming Lei wrote:
> > sqe->flags is u8, and now we have used 7 bits, so take the last one for
> > extending purpose.
> > 
> > If bit7(IOSQE_HAS_EXT_FLAGS_BIT) is 1, it means this sqe carries ext flags
> > from the last byte(.ext_flags), or bit23~bit16 of sqe->uring_cmd_flags for
> > IORING_OP_URING_CMD.
> > 
> > io_slot_flags() return value is converted to `ULL` because the affected bits
> > are beyond 32bit now.
> 
> If we're extending flags, which is something we arguably need to do at
> some point, I think we should have them be generic and not spread out.

Sorry, maybe I don't get your idea, and the ext_flag itself is always
initialized in io_init_req(), like normal sqe->flags, same with its
usage.

> If uring_cmd needs specific flags and don't have them, then we should
> add it just for that.

The only difference is that bit23~bit16 of sqe->uring_cmd_flags is
borrowed for uring_cmd's ext flags, because sqe byte0~47 have been taken,
and can't be reused for generic flag. If we want to use byte48~63, it has
to be overlapped with uring_cmd's payload, and it is one generic sqe
flag, which is applied on uring_cmd too.

That is the only way I thought of, or any other suggestion for extending sqe
flags generically?


Thanks,
Ming