[PATCH v1 08/54] block: comment on bio_alloc_pages()

From: Ming Lei <tom.leiming@gmail.com>
To: Jens Axboe <axboe@fb.com>, linux-kernel@vger.kernel.org
Cc: linux-block@vger.kernel.org,
	Christoph Hellwig <hch@infradead.org>,
	Ming Lei <tom.leiming@gmail.com>, Jens Axboe <axboe@kernel.dk>,
	Kent Overstreet <kent.overstreet@gmail.com>,
	Shaohua Li <shli@kernel.org>, Mike Christie <mchristi@redhat.com>,
	Guoqing Jiang <gqjiang@suse.com>, Hannes Reinecke <hare@suse.com>,
	linux-bcache@vger.kernel.org (open list:BCACHE (BLOCK LAYER
	CACHE)),
	linux-raid@vger.kernel.org (open list:SOFTWARE RAID (Multiple
	Disks) SUPPORT)
Subject: [PATCH v1 08/54] block: comment on bio_alloc_pages()
Date: Tue, 27 Dec 2016 23:55:57 +0800	[thread overview]
Message-ID: <1482854250-13481-9-git-send-email-tom.leiming@gmail.com> (raw)
In-Reply-To: <1482854250-13481-1-git-send-email-tom.leiming@gmail.com>

This patch adds comment on usage of bio_alloc_pages(),
also comments on one special case of bch_data_verify().

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 block/bio.c               | 4 +++-
 drivers/md/bcache/debug.c | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index 2b375020fc49..d4a1e0b63ea0 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -961,7 +961,9 @@ EXPORT_SYMBOL(bio_advance);
  * @bio: bio to allocate pages for
  * @gfp_mask: flags for allocation
  *
- * Allocates pages up to @bio->bi_vcnt.
+ * Allocates pages up to @bio->bi_vcnt, and this function should only
+ * be called on a new initialized bio, which means all pages aren't added
+ * to the bio via bio_add_page() yet.
  *
  * Returns 0 on success, -ENOMEM on failure. On failure, any allocated pages are
  * freed.
diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c
index 06f55056aaae..48d03e8b3385 100644
--- a/drivers/md/bcache/debug.c
+++ b/drivers/md/bcache/debug.c
@@ -110,6 +110,12 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
 	struct bio_vec bv, cbv;
 	struct bvec_iter iter, citer = { 0 };
 
+	/*
+	 * Once multipage bvec is supported, the bio_clone()
+	 * has to make sure page count in this bio can be held
+	 * in the new cloned bio because each single page need
+	 * to assign to each bvec of the new bio.
+	 */
 	check = bio_clone(bio, GFP_NOIO);
 	if (!check)
 		return;
-- 
2.7.4
