[RFC PATCH 06/11] block: add new field into 'struct bvec_iter'

From: Ming Lei <ming.lei@redhat.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
	Jeffle Xu <jefflexu@linux.alibaba.com>,
	Mike Snitzer <snitzer@redhat.com>,
	dm-devel@redhat.com, Ming Lei <ming.lei@redhat.com>
Subject: [RFC PATCH 06/11] block: add new field into 'struct bvec_iter'
Date: Tue, 16 Mar 2021 11:15:18 +0800	[thread overview]
Message-ID: <20210316031523.864506-7-ming.lei@redhat.com> (raw)
In-Reply-To: <20210316031523.864506-1-ming.lei@redhat.com>

There is a hole at the end of 'struct bvec_iter', so put a new field
here and we can save cookie returned from submit_bio() here for
supporting bio based polling.

This way can avoid to extend bio unnecessarily.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/linux/bvec.h | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/include/linux/bvec.h b/include/linux/bvec.h
index ff832e698efb..61c0f55f7165 100644
--- a/include/linux/bvec.h
+++ b/include/linux/bvec.h
@@ -43,6 +43,15 @@ struct bvec_iter {
 
 	unsigned int            bi_bvec_done;	/* number of bytes completed in
 						   current bvec */
+
+	/*
+	 * There is a hole at the end of bvec_iter, define one filed to
+	 * hold something which isn't relate with 'bvec_iter', so that we can
+	 * avoid to extend bio. So far this new field is used for bio based
+	 * pooling, we will store returning value of underlying queue's
+	 * submit_bio() here.
+	 */
+	unsigned int		bi_private_data;
 };
 
 struct bvec_iter_all {
-- 
2.29.2

