Re: [PATCH v4 07/11] io_uring/rw: add support to send meta along with read/write

[Christoph Hellwig <hch@lst.de>]

s/meta/metadata/ in the subject.

> +	const struct io_uring_meta *md = (struct io_uring_meta *)sqe->big_sqe_cmd;

Overly long line.

> +	if (!meta_type)
> +		return 0;
> +	if (!(meta_type & META_TYPE_INTEGRITY))
> +		return -EINVAL;

What is the meta_type for?  To distintinguish PI from non-PI metadata?
Why doesn't this support non-PI metadata?  Also PI or TO_PI might be
a better name than the rather generic integrity.  (but I'll defer to
Martin if he has any good arguments for naming here).

>  static bool need_complete_io(struct io_kiocb *req)
>  {
> +	struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
> +
> +	/* Exclude meta IO as we don't support partial completion for that */
>  	return req->flags & REQ_F_ISREG ||
> -		S_ISBLK(file_inode(req->file)->i_mode);
> +		S_ISBLK(file_inode(req->file)->i_mode) ||
> +		!(rw->kiocb.ki_flags & IOCB_HAS_METADATA);
>  }

What partial ocmpletions aren't supported?  Note that this would
trigger easily as right now metadata is only added for block devices
anyway.

> +	if (unlikely(kiocb->ki_flags & IOCB_HAS_METADATA)) {

For a workload using metadata this is everything but unlikely.  Is
there a specific reason you're trying to override the existing
branch predictor here (although on at least x86_64 gcc these kinds
of unlikely calls tend to be no-ops anyway).

> +		struct io_async_rw *io = req->async_data;
> +
> +		if (!(req->file->f_flags & O_DIRECT))
> +			return -EOPNOTSUPP;

I guess you are forcing this here rather in the file oerations instance
because the union of the field in struct io_async_rw.  Please add comment
about that.

> +	/* wpq is for buffered io, while meta fields are used with direct io*/

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