[PATCH] queue merge_bvec_fn() changes

Make merge_bvec_fn() return number of bytes we can accept at a given
offset, instead of a bool.

drivers/md/linear.c

@@ -52,19 +52,21 @@ static inline dev_info_t *which_dev(mddev_t *mddev, sector_t sector)
  *	@bio: the buffer head that's been built up so far
  *	@biovec: the request that could be merged to it.
  *
- *	Return 1 if the merge is not permitted (because the
- *	result would cross a device boundary), 0 otherwise.
+ *	Return amount of bytes we can take at this offset
  */
 static int linear_mergeable_bvec(request_queue_t *q, struct bio *bio, struct bio_vec *biovec)
 {
 	mddev_t *mddev = q->queuedata;
-	dev_info_t *dev0, *dev1;
+	dev_info_t *dev0;
+	int maxsectors, bio_sectors = (bio->bi_size + biovec->bv_len) >> 9;
 
 	dev0 = which_dev(mddev, bio->bi_sector);
-	dev1 = which_dev(mddev, bio->bi_sector +
-			        ((bio->bi_size + biovec->bv_len - 1) >> 9));
+	maxsectors = (dev0->size << 1) - (bio->bi_sector - (dev0->offset<<1));
 
-	return dev0 != dev1;
+	if (bio_sectors <= maxsectors)
+		return biovec->bv_len;
+
+	return (maxsectors << 9) - bio->bi_size;
 }
 
 static int linear_run (mddev_t *mddev)

drivers/md/raid0.c

@@ -168,8 +168,7 @@ static int create_strip_zones (mddev_t *mddev)
  *	@bio: the buffer head that's been built up so far
  *	@biovec: the request that could be merged to it.
  *
- *	Return 1 if the merge is not permitted (because the
- *	result would cross a chunk boundary), 0 otherwise.
+ *	Return amount of bytes we can accept at this offset
  */
 static int raid0_mergeable_bvec(request_queue_t *q, struct bio *bio, struct bio_vec *biovec)
 {
@@ -182,7 +181,7 @@ static int raid0_mergeable_bvec(request_queue_t *q, struct bio *bio, struct bio_
 	block = bio->bi_sector >> 1;
 	bio_sz = (bio->bi_size + biovec->bv_len) >> 10;
 
-	return chunk_size < ((block & (chunk_size - 1)) + bio_sz);
+	return (chunk_size - ((block & (chunk_size - 1)) + bio_sz)) << 10;
 }
 
 static int raid0_run (mddev_t *mddev)

fs/bio.c

@@ -354,7 +354,7 @@ int bio_get_nr_vecs(struct block_device *bdev)
 	request_queue_t *q = bdev_get_queue(bdev);
 	int nr_pages;
 
-	nr_pages = q->max_sectors >> (PAGE_SHIFT - 9);
+	nr_pages = ((q->max_sectors << 9) + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (nr_pages > q->max_phys_segments)
 		nr_pages = q->max_phys_segments;
 	if (nr_pages > q->max_hw_segments)
@@ -385,13 +385,13 @@ int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
 	 * cloned bio must not modify vec list
 	 */
 	if (unlikely(bio_flagged(bio, BIO_CLONED)))
-		return 1;
+		return 0;
 
 	if (bio->bi_vcnt >= bio->bi_max_vecs)
-		return 1;
+		return 0;
 
 	if (((bio->bi_size + len) >> 9) > q->max_sectors)
-		return 1;
+		return 0;
 
 	/*
 	 * we might loose a segment or two here, but rather that than
@@ -404,7 +404,7 @@ int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
 
 	if (fail_segments) {
 		if (retried_segments)
-			return 1;
+			return 0;
 
 		bio->bi_flags &= ~(1 << BIO_SEG_VALID);
 		retried_segments = 1;
@@ -425,18 +425,24 @@ int bio_add_page(struct bio *bio, struct page *page, unsigned int len,
 	 * depending on offset), it can specify a merge_bvec_fn in the
 	 * queue to get further control
 	 */
-	if (q->merge_bvec_fn && q->merge_bvec_fn(q, bio, bvec)) {
+	if (q->merge_bvec_fn) {
+		/*
+		 * merge_bvec_fn() returns number of bytes it can accept
+		 * at this offset
+		 */
+		if (q->merge_bvec_fn(q, bio, bvec) < len) {
 			bvec->bv_page = NULL;
 			bvec->bv_len = 0;
 			bvec->bv_offset = 0;
-		return 1;
+			return 0;
+		}
 	}
 
 	bio->bi_vcnt++;
 	bio->bi_phys_segments++;
 	bio->bi_hw_segments++;
 	bio->bi_size += len;
-	return 0;
+	return len;
 }
 
 /**

fs/direct-io.c

@@ -417,12 +417,12 @@ dio_bio_add_page(struct dio *dio, struct page *page,
 
 	/* Take a ref against the page each time it is placed into a BIO */
 	page_cache_get(page);
-	if (bio_add_page(dio->bio, page, bv_len, bv_offset)) {
+	if (bio_add_page(dio->bio, page, bv_len, bv_offset) < bv_len) {
 		dio_bio_submit(dio);
 		ret = dio_new_bio(dio, blkno);
 		if (ret == 0) {
 			ret = bio_add_page(dio->bio, page, bv_len, bv_offset);
-			BUG_ON(ret != 0);
+			BUG_ON(ret < bv_len);
 		} else {
 			/* The page didn't make it into a BIO */
 			page_cache_release(page);

fs/mpage.c

@@ -176,6 +176,7 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 	unsigned first_hole = blocks_per_page;
 	struct block_device *bdev = NULL;
 	struct buffer_head bh;
+	int length;
 
 	if (page_has_buffers(page))
 		goto confused;
@@ -233,7 +234,8 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 			goto confused;
 	}
 
-	if (bio_add_page(bio, page, first_hole << blkbits, 0)) {
+	length = first_hole << blkbits;
+	if (bio_add_page(bio, page, length, 0) < length) {
 		bio = mpage_bio_submit(READ, bio);
 		goto alloc_new;
 	}
@@ -334,6 +336,7 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 	int boundary = 0;
 	sector_t boundary_block = 0;
 	struct block_device *boundary_bdev = NULL;
+	int length;
 
 	if (page_has_buffers(page)) {
 		struct buffer_head *head = page_buffers(page);
@@ -467,7 +470,8 @@ mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 			try_to_free_buffers(page);
 	}
 
-	if (bio_add_page(bio, page, first_unmapped << blkbits, 0)) {
+	length = first_unmapped << blkbits;
+	if (bio_add_page(bio, page, length, 0) < length) {
 		bio = mpage_bio_submit(WRITE, bio);
 		goto alloc_new;
 	}

fs/xfs/pagebuf/page_buf.c

@@ -1448,7 +1448,7 @@ pagebuf_iorequest(			/* start real I/O		*/
 		if (nbytes > size)
 			nbytes = size;
 
-		if (bio_add_page(bio, pb->pb_pages[map_i], nbytes, offset))
+		if (bio_add_page(bio, pb->pb_pages[map_i], nbytes, offset) < nbytes)
 			break;
 
 		offset = 0;