linux-kernel - [PATCH v1 08/54] block: comment on bio_alloc

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Date:   Tue, 27 Dec 2016 23:55:57 +0800
From:   Ming Lei <tom.leiming@...il.com>
To:     Jens Axboe <axboe@...com>, linux-kernel@...r.kernel.org
Cc:     linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
        Ming Lei <tom.leiming@...il.com>, Jens Axboe <axboe@...nel.dk>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Shaohua Li <shli@...nel.org>,
        Mike Christie <mchristi@...hat.com>,
        Guoqing Jiang <gqjiang@...e.com>,
        Hannes Reinecke <hare@...e.com>,
        linux-bcache@...r.kernel.org (open list:BCACHE (BLOCK LAYER CACHE)),
        linux-raid@...r.kernel.org (open list:SOFTWARE RAID (Multiple Disks)
        SUPPORT)
Subject: [PATCH v1 08/54] block: comment on bio_alloc_pages()

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@...il.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