Re: [PATCH v4 1/5] fs,io_uring: add infrastructure for uring-cmd

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

On Thu, May 05, 2022 at 06:52:25AM -0600, Jens Axboe wrote:
> On 5/5/22 12:06 AM, Kanchan Joshi wrote:
> > From: Jens Axboe <axboe@kernel.dk>
> > 
> > file_operations->uring_cmd is a file private handler.
> > This is somewhat similar to ioctl but hopefully a lot more sane and
> > useful as it can be used to enable many io_uring capabilities for the
> > underlying operation.
> > 
> > IORING_OP_URING_CMD is a file private kind of request. io_uring doesn't
> > know what is in this command type, it's for the provider of ->uring_cmd()
> > to deal with. This operation can be issued only on the ring that is
> > setup with both IORING_SETUP_SQE128 and IORING_SETUP_CQE32 flags.
> 
> One thing that occured to me that I think we need to change is what you
> mention above, code here:
> 
> > +static int io_uring_cmd_prep(struct io_kiocb *req,
> > +			     const struct io_uring_sqe *sqe)
> > +{
> > +	struct io_uring_cmd *ioucmd = &req->uring_cmd;
> > +	struct io_ring_ctx *ctx = req->ctx;
> > +
> > +	if (ctx->flags & IORING_SETUP_IOPOLL)
> > +		return -EOPNOTSUPP;
> > +	/* do not support uring-cmd without big SQE/CQE */
> > +	if (!(ctx->flags & IORING_SETUP_SQE128))
> > +		return -EOPNOTSUPP;
> > +	if (!(ctx->flags & IORING_SETUP_CQE32))
> > +		return -EOPNOTSUPP;
> > +	if (sqe->ioprio || sqe->rw_flags)
> > +		return -EINVAL;
> > +	ioucmd->cmd = sqe->cmd;
> > +	ioucmd->cmd_op = READ_ONCE(sqe->cmd_op);
> > +	return 0;
> > +}
> 
> I've been thinking of this mostly in the context of passthrough for
> nvme, but it originally started as a generic feature to be able to wire
> up anything for these types of commands. The SQE128/CQE32 requirement is
> really an nvme passthrough restriction, we don't necessarily need this
> for any kind of URING_CMD. Ditto IOPOLL as well. These are all things
> that should be validated further down, but there's no way to do that
> currently.
> 
> Let's not have that hold up merging this, but we do need it fixed up for
> 5.19-final so we don't have this restriction. Suggestions welcome...

The validation has to be done in consumer of SQE128/CQE32(nvme). One way is
to add SQE128/CQE32 io_uring_cmd_flags and pass them via ->uring_cmd(issue_flags).


Thanks,
Ming