linux-kernel - [PATCH 1/2] block: handle the null_mapped flag correctly in blk_rq_map_user

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Date:	Wed, 11 Feb 2015 14:07:49 +0100
From:	Christoph Hellwig <hch@....de>
To:	Jens Axboe <axboe@...com>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] block: handle the null_mapped flag correctly in blk_rq_map_user_iov

The tape drivers (and the sg driver in a special case that doesn't matter
here) use the null_mapped flag to tell blk_rq_map_user to not copy around
any data into or out of the bounce buffers.  blk_rq_map_user_iov never
got that treatment, which didn't matter until I refactored blk_rq_map_user
to be implemented in terms of blk_rq_map_user_iov.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 block/blk-map.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/blk-map.c b/block/blk-map.c
index 0f22911..b8d2725 100644
--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -93,6 +93,9 @@ int blk_rq_map_user_iov(struct request_queue *q, struct request *rq,
 	if (IS_ERR(bio))
 		return PTR_ERR(bio);
 
+	if (map_data && map_data->null_mapped)
+		bio->bi_flags |= (1 << BIO_NULL_MAPPED);
+
 	if (bio->bi_iter.bi_size != iter->count) {
 		/*
 		 * Grab an extra reference to this bio, as bio_unmap_user()
-- 
1.9.1

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