linux-kernel - Re: [PATCH v5 3/9] iov_iter: Use IOCB/IOMAP_WRITE if available rather than iterator direction

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Message-ID: <Y7+8r1IYQS3sbbVz@infradead.org>
Date:   Wed, 11 Jan 2023 23:54:23 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/9] iov_iter: Use IOCB/IOMAP_WRITE if available
 rather than iterator direction

On Wed, Jan 11, 2023 at 02:27:58PM +0000, David Howells wrote:
> This allows all but three of the users of iov_iter_rw() to be got rid of: a
> consistency check and a warning statement in cifs

Let's just drop these two.

> and one user in the block
> layer that has neither available.

And use the information in the request for this one (see patch below),
and then move this patch first in the series, add an explicit direction
parameter in the gup_flags to the get/pin helper and drop iov_iter_rw
and the whole confusing source/dest information in the iov_iter entirely,
which is a really nice big tree wide cleanup that remove redundant
information.

---
diff --git a/block/blk-map.c b/block/blk-map.c
index 19940c978c73bb..08cbb7ff3b196d 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -203,7 +203,7 @@ static int bio_copy_user_iov(struct request *rq, struct rq_map_data *map_data,
 	/*
 	 * success
 	 */
-	if ((iov_iter_rw(iter) == WRITE &&
+	if ((op_is_write(rq->cmd_flags) &&
 	     (!map_data || !map_data->null_mapped)) ||
 	    (map_data && map_data->from_user)) {
 		ret = bio_copy_from_iter(bio, iter);