From: Milan Broz <mbroz@redhat.com>

This patch implements biovec merge function for linear target.

If the underlying device has merge function defined, call it.
If not, keep precomputed value.

Signed-off-by: Milan Broz <mbroz@redhat.com>

---

 drivers/md/dm-linear.c |   38 ++++++++++++++++++++++++++++++++++----
 1 files changed, 34 insertions(+), 4 deletions(-)

Index: linux-2.6.21/drivers/md/dm-linear.c
===================================================================
--- linux-2.6.21.orig/drivers/md/dm-linear.c	2007-05-01 17:38:30.000000000 +0100
+++ linux-2.6.21/drivers/md/dm-linear.c	2007-05-01 17:40:58.000000000 +0100
@@ -69,13 +69,18 @@ static void linear_dtr(struct dm_target 
 	kfree(lc);
 }
 
-static int linear_map(struct dm_target *ti, struct bio *bio,
-		      union map_info *map_context)
+static void linear_map_bio(struct dm_target *ti, struct bio *bio)
 {
-	struct linear_c *lc = (struct linear_c *) ti->private;
+	struct linear_c *lc = ti->private;
 
 	bio->bi_bdev = lc->dev->bdev;
 	bio->bi_sector = lc->start + (bio->bi_sector - ti->begin);
+}
+
+static int linear_map(struct dm_target *ti, struct bio *bio,
+		      union map_info *map_context)
+{
+	linear_map_bio(ti, bio);
 
 	return DM_MAPIO_REMAPPED;
 }
@@ -114,15 +119,40 @@ static int linear_ioctl(struct dm_target
 	return blkdev_driver_ioctl(bdev->bd_inode, &fake_file, bdev->bd_disk, cmd, arg);
 }
 
+static int linear_merge(struct dm_target *ti, struct bio *bio,
+			struct bio_vec *biovec, int len)
+{
+	struct linear_c *lc = ti->private;
+	request_queue_t *q = bdev_get_queue(lc->dev->bdev);
+
+	if (q->merge_bvec_fn) {
+		/* FIXME Yuck.  Shouldn't these be merge_bvec_fn parameters?  Why does the bio get passed around here at all? */
+		/* FIXME Use helper function (or macro) to save this for now. */
+		sector_t org_sec = bio->bi_sector;
+		struct block_device *org_dev = bio->bi_bdev;
+
+		linear_map_bio(ti, bio);
+
+		len = q->merge_bvec_fn(q, bio, biovec);
+
+		/* FIXME Use helper function to restore this */
+		bio->bi_bdev = org_dev;
+		bio->bi_sector = org_sec;
+	}
+
+	return len;
+}
+
 static struct target_type linear_target = {
 	.name   = "linear",
-	.version= {1, 0, 2},
+	.version= {1, 0, 3},
 	.module = THIS_MODULE,
 	.ctr    = linear_ctr,
 	.dtr    = linear_dtr,
 	.map    = linear_map,
 	.status = linear_status,
 	.ioctl  = linear_ioctl,
+	.merge  = linear_merge,
 };
 
 int __init dm_linear_init(void)