block: support multipage bvec

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)

The incoming bio may be too big to be cloned into
one singlepage bvecs bio, so split the bio and
check the splitted bio one by one.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/md/bcache/debug.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c
index 48d03e8b3385..18b2d2d138e3 100644
--- a/drivers/md/bcache/debug.c
+++ b/drivers/md/bcache/debug.c

@@ -103,7 +103,7 @@ void bch_btree_verify(struct btree *b)
 	up(&b->io_mutex);
 }
 
-void bch_data_verify(struct cached_dev *dc, struct bio *bio)
+static void __bch_data_verify(struct cached_dev *dc, struct bio *bio)
 {
 	char name[BDEVNAME_SIZE];
 	struct bio *check;

@@ -116,7 +116,7 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
 	 * 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);
+	check = bio_clone_sp(bio, GFP_NOIO);
 	if (!check)
 		return;
 	check->bi_opf = REQ_OP_READ;

@@ -151,6 +151,26 @@ void bch_data_verify(struct cached_dev *dc, struct bio *bio)
 	bio_put(check);
 }
 
+void bch_data_verify(struct cached_dev *dc, struct bio *bio)
+{
+	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
+	struct bio *clone = bio_clone_fast(bio, GFP_NOIO, q->bio_split);
+	unsigned sectors;

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)

Looks all are safe after multipage bvec is supported.

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
---
 drivers/md/bcache/btree.c | 1 +
 drivers/md/bcache/super.c | 6 ++++++
 drivers/md/bcache/util.c  | 7 +++++++
 3 files changed, 14 insertions(+)

diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index a43eedd5804d..fc35cfb4d0f1 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c

@@ -428,6 +428,7 @@ static void do_btree_node_write(struct btree *b)
 
 		continue_at(cl, btree_node_write_done, NULL);
 	} else {
+		/* No harm for multipage bvec since the new is just allocated */
 		b->bio->bi_vcnt = 0;
 		bch_bio_map(b->bio, i);
 

diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 3a19cbc8b230..607b022259dc 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c

@@ -208,6 +208,7 @@ static void write_bdev_super_endio(struct bio *bio)
 
 static void __write_super(struct cache_sb *sb, struct bio *bio)
 {
+	/* single page bio, safe for multipage bvec */
 	struct cache_sb *out = page_address(bio->bi_io_vec[0].bv_page);
 	unsigned i;
 

@@ -1156,6 +1157,8 @@ static void register_bdev(struct cache_sb *sb, struct page *sb_page,
 	dc->bdev->bd_holder = dc;
 
 	bio_init(&dc->sb_bio, dc->sb_bio.bi_inline_vecs, 1);
+
+	/* single page bio, safe for multipage bvec */
 	dc->sb_bio.bi_io_vec[0].bv_page = sb_page;