md: add block tracing for bio_remapping

The block tracing infrastructure (accessed with blktrace/blkparse)
supports the tracing of mapping bios from one device to another.
This is currently used when a bio in a partition is mapped to the
whole device, when bios are mapped by dm, and for mapping in md/raid5.
Other md personalities do not include this tracing yet, so add it.

When a read-error is detected we redirect the request to a different device.
This could justifiably be seen as a new mapping for the originial bio,
or a secondary mapping for the bio that errors.  This patch uses
the second option.

When md is used under dm-raid, the mappings are not traced as we do
not have access to the block device number of the parent.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/drivers/md/linear.c b/drivers/md/linear.c
index 9c7d4f5483ea..5975c9915684 100644
--- a/drivers/md/linear.c
+++ b/drivers/md/linear.c
@@ -21,6 +21,7 @@
 #include <linux/seq_file.h>
 #include <linux/module.h>
 #include <linux/slab.h>
+#include <trace/events/block.h>
 #include "md.h"
 #include "linear.h"
 
@@ -227,22 +228,22 @@ static void linear_make_request(struct mddev *mddev, struct bio *bio)
 	}
 
 	do {
-		tmp_dev = which_dev(mddev, bio->bi_iter.bi_sector);
+		sector_t bio_sector = bio->bi_iter.bi_sector;
+		tmp_dev = which_dev(mddev, bio_sector);
 		start_sector = tmp_dev->end_sector - tmp_dev->rdev->sectors;
 		end_sector = tmp_dev->end_sector;
 		data_offset = tmp_dev->rdev->data_offset;
 		bio->bi_bdev = tmp_dev->rdev->bdev;
 
-		if (unlikely(bio->bi_iter.bi_sector >= end_sector ||
-			     bio->bi_iter.bi_sector < start_sector))
+		if (unlikely(bio_sector >= end_sector ||
+			     bio_sector < start_sector))
 			goto out_of_bounds;
 
 		if (unlikely(bio_end_sector(bio) > end_sector)) {
 			/* This bio crosses a device boundary, so we have to
 			 * split it.
 			 */
-			split = bio_split(bio, end_sector -
-					  bio->bi_iter.bi_sector,
+			split = bio_split(bio, end_sector - bio_sector,
 					  GFP_NOIO, fs_bio_set);
 			bio_chain(split, bio);
 		} else {
@@ -256,8 +257,13 @@ static void linear_make_request(struct mddev *mddev, struct bio *bio)
 			 !blk_queue_discard(bdev_get_queue(split->bi_bdev)))) {
 			/* Just ignore it */
 			bio_endio(split);
-		} else
+		} else {
+			if (mddev->gendisk)
+				trace_block_bio_remap(bdev_get_queue(split->bi_bdev),
+						      split, disk_devt(mddev->gendisk),
+						      bio_sector);
 			generic_make_request(split);
+		}
 	} while (split != bio);
 	return;