btrfs: record btrfs_device directly in btrfs_io_bio

Instead of recording stripe_index and using that to access correct
btrfs_device from btrfs_bio::stripes record the btrfs_device in
btrfs_io_bio. This will enable endio handlers to increment device
error counters on checksum errors.
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/raid56.c

@@ -1117,6 +1117,7 @@ static int rbio_add_io_page(struct btrfs_raid_bio *rbio,
 
 	/* put a new bio on the list */
 	bio = btrfs_io_bio_alloc(bio_max_len >> PAGE_SHIFT ?: 1);
+	btrfs_io_bio(bio)->device = stripe->dev;
 	bio->bi_iter.bi_size = 0;
 	bio_set_dev(bio, stripe->dev->bdev);
 	bio->bi_iter.bi_sector = disk_start >> 9;

fs/btrfs/volumes.c

@@ -6261,12 +6261,8 @@ static void btrfs_end_bio(struct bio *bio)
 		atomic_inc(&bbio->error);
 		if (bio->bi_status == BLK_STS_IOERR ||
 		    bio->bi_status == BLK_STS_TARGET) {
-			unsigned int stripe_index =
-				btrfs_io_bio(bio)->stripe_index;
-			struct btrfs_device *dev;
+			struct btrfs_device *dev = btrfs_io_bio(bio)->device;
 
-			BUG_ON(stripe_index >= bbio->num_stripes);
-			dev = bbio->stripes[stripe_index].dev;
 			if (dev->bdev) {
 				if (bio_op(bio) == REQ_OP_WRITE)
 					btrfs_dev_stat_inc_and_print(dev,
@@ -6313,13 +6309,12 @@ static void btrfs_end_bio(struct bio *bio)
 }
 
 static void submit_stripe_bio(struct btrfs_bio *bbio, struct bio *bio,
-			      u64 physical, int dev_nr)
+			      u64 physical, struct btrfs_device *dev)
 {
-	struct btrfs_device *dev = bbio->stripes[dev_nr].dev;
 	struct btrfs_fs_info *fs_info = bbio->fs_info;
 
 	bio->bi_private = bbio;
-	btrfs_io_bio(bio)->stripe_index = dev_nr;
+	btrfs_io_bio(bio)->device = dev;
 	bio->bi_end_io = btrfs_end_bio;
 	bio->bi_iter.bi_sector = physical >> 9;
 	btrfs_debug_in_rcu(fs_info,
@@ -6420,8 +6415,7 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info *fs_info, struct bio *bio,
 		else
 			bio = first_bio;
 
-		submit_stripe_bio(bbio, bio, bbio->stripes[dev_nr].physical,
-				  dev_nr);
+		submit_stripe_bio(bbio, bio, bbio->stripes[dev_nr].physical, dev);
 	}
 	btrfs_bio_counter_dec(fs_info);
 	return BLK_STS_OK;

fs/btrfs/volumes.h

@@ -288,7 +288,7 @@ struct btrfs_fs_devices {
  */
 struct btrfs_io_bio {
 	unsigned int mirror_num;
-	unsigned int stripe_index;
+	struct btrfs_device *device;
 	u64 logical;
 	u8 *csum;
 	u8 csum_inline[BTRFS_BIO_INLINE_CSUM_SIZE];