Re: [PATCH 3/4] io_uring: add IORING_OP_READ[WRITE]_SPLICE_BUF

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

On Sat, Feb 11, 2023 at 10:13:37AM -0700, Jens Axboe wrote:
> On 2/10/23 8:32?AM, Ming Lei wrote:
> 
> One more comment on this.
> 
> > +static int __io_prep_rw_splice_buf(struct io_kiocb *req,
> > +				   struct io_rw_splice_buf_data *data,
> > +				   struct file *splice_f,
> > +				   size_t len,
> > +				   loff_t splice_off)
> > +{
> > +	unsigned flags = req->opcode == IORING_OP_READ_SPLICE_BUF ?
> > +			SPLICE_F_KERN_FOR_READ : SPLICE_F_KERN_FOR_WRITE;
> > +	struct splice_desc sd = {
> > +		.total_len = len,
> > +		.flags = flags | SPLICE_F_NONBLOCK | SPLICE_F_KERN_NEED_CONFIRM,
> > +		.pos = splice_off,
> > +		.u.data = data,
> > +		.ignore_sig = true,
> > +	};
> > +
> > +	return splice_direct_to_actor(splice_f, &sd,
> > +			io_splice_buf_direct_actor);
> 
> Is this safe? We end up using current->splice_pipe here, which should be
> fine as long as things are left in a sane state after every operation.
> Which they should be, just like a syscall would. Just wanted to make
> sure you've considered that part.

Yeah.

Direct pipe is always left as empty when splice_direct_to_actor()
returns. Pipe buffers(pages) are produced from ->splice_read()
called from splice_direct_to_actor(), and consumed by
io_splice_buf_direct_actor().

If any error is returned, direct pipe is empty too, and we just
need to drop reference of sliced pages by io_rw_cleanup_splice_buf().


Thanks,
Ming