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SubjectRe: [PATCH v5 5/5] block: loop: support DIO & AIO
> +	int ret;
> +
> + /* nomerge for loop request queue */
> + WARN_ON(cmd->rq->bio != cmd->rq->biotail);
> +
> + bvec = __bvec_iter_bvec(bio->bi_io_vec, bio->bi_iter);
> + iov_iter_bvec(&iter, ITER_BVEC | rw, bvec,
> + bio_segments(bio), blk_rq_bytes(cmd->rq));
> +
> + cmd->iocb.ki_pos = pos;
> + cmd->iocb.ki_filp = file;
> + cmd->iocb.ki_complete = lo_rw_aio_complete;
> + cmd->iocb.ki_flags = IOCB_DIRECT;
> +
> + if (rw == WRITE)
> + ret = file->f_op->write_iter(&cmd->iocb, &iter);
> + else
> + ret = file->f_op->read_iter(&cmd->iocb, &iter);

I think we really need a vfs_ wrapper here similar to what I did a while
ago, e.g. vfs_iter_read/write_async.

> +static inline int lo_rw_simple(struct loop_device *lo,
> + struct request *rq, loff_t pos, bool rw)
> +{
> + struct loop_cmd *cmd = blk_mq_rq_to_pdu(rq);
> +
> + if (cmd->use_aio)
> + return lo_rw_aio(lo, cmd, pos, rw);
> +
> + if (rw == WRITE)
> + return lo_write_simple(lo, rq, pos);
> + else
> + return lo_read_simple(lo, rq, pos);
> +}

And the io_submit style read/write also works for buffered I/O, so no
need to keep lo_write_simple/lo_read_simple around.

> @@ -1569,7 +1634,8 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
> failed:
> if (ret)
> cmd->rq->errors = -EIO;
> - blk_mq_complete_request(cmd->rq);
> + if (!cmd->use_aio || ret)
> + blk_mq_complete_request(cmd->rq);

If you don't complete the request here setting req->error doesn't
make sense. I'd suggest to move the blk_mq_complete_request for
everything but the trivial error case into the actual I/O handlers
to clean this up a bit, too.



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