Re: [PATCH 4/8] io_uring: add support for futex wake and wait

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jul 13, 2023 at 01:15:13PM +0200, Peter Zijlstra wrote:
> On Wed, Jul 12, 2023 at 10:20:13AM -0600, Jens Axboe wrote:
> 
> > +int io_futex_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
> > +{
> > +	struct io_futex *iof = io_kiocb_to_cmd(req, struct io_futex);
> > +
> > +	if (unlikely(sqe->addr2 || sqe->buf_index || sqe->addr3))
> > +		return -EINVAL;
> > +
> > +	iof->futex_op = READ_ONCE(sqe->fd);
> > +	iof->uaddr = u64_to_user_ptr(READ_ONCE(sqe->addr));
> > +	iof->futex_val = READ_ONCE(sqe->len);
> > +	iof->futex_mask = READ_ONCE(sqe->file_index);
> > +	iof->futex_flags = READ_ONCE(sqe->futex_flags);
> > +	if (iof->futex_flags & FUTEX_CMD_MASK)
> > +		return -EINVAL;
> > +
> > +	return 0;
> > +}
> 
> I'm a little confused on the purpose of iof->futex_op, it doesn't appear
> to be used. Instead iof->futex_flags is used as the ~FUTEX_CMD_MASK part
> of ops.
> 
> The latter actually makes sense since you encode the actual op in the
> IOURING_OP_ space.

Futex is slowly getting back to me; I'm thinking these io_uring
interfaces should perhaps use the futex2 flags instead of the futex_op
encoded muck.

I'll try and send out a few patches tomorrow to clarify things a little
-- the futex2 work seems to have stalled somewhere halfway :/