[PATCH v2] dm dust: make badblock messages target-relative

[Samuel Moelius]

dm-dust currently treats addbadblock, removebadblock and queryblock
arguments as block numbers on the underlying device. That is surprising
for a device-mapper target: a dm-dust table with a non-zero backing
offset can add bad blocks that are outside the mapped target, and a
badblock added for logical block 0 is missed because the I/O path checks
the remapped backing-device block instead.

Interpret badblock message arguments as blocks relative to the start of
the dm-dust target instead. Bound the arguments by the target length and
perform badblock lookup using target-relative sectors before remapping
the bio to the underlying device.

This intentionally changes the non-zero backing-offset behavior to make
the badblock control interface match the mapped dm-dust device, rather
than the underlying device.

Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <sam.moelius@xxxxxxxxxxxxxxx>
---
Changes in v2:
  - Revise commit message
  - Remove call to sector_div() in __dust_map_write()

 drivers/md/dm-dust.c | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/drivers/md/dm-dust.c b/drivers/md/dm-dust.c
index c7e3077fb1f5..954f4ec5a51c 100644
--- a/drivers/md/dm-dust.c
+++ b/drivers/md/dm-dust.c
@@ -196,7 +196,6 @@ static int __dust_map_write(struct dust_device *dd, sector_t thisblock)
 		dd->badblock_count--;
 		kfree(bblk);
 		if (!dd->quiet_mode) {
-			sector_div(thisblock, dd->sect_per_block);
 			DMINFO("block %llu removed from badblocklist by write",
 			       (unsigned long long)thisblock);
 		}
@@ -224,15 +223,16 @@ static int dust_map_write(struct dust_device *dd, sector_t thisblock,
 static int dust_map(struct dm_target *ti, struct bio *bio)
 {
 	struct dust_device *dd = ti->private;
+	sector_t dust_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);
 	int r;
 
 	bio_set_dev(bio, dd->dev->bdev);
-	bio->bi_iter.bi_sector = dd->start + dm_target_offset(ti, bio->bi_iter.bi_sector);
+	bio->bi_iter.bi_sector = dd->start + dust_sector;
 
 	if (bio_data_dir(bio) == READ)
-		r = dust_map_read(dd, bio->bi_iter.bi_sector, dd->fail_read_on_bb);
+		r = dust_map_read(dd, dust_sector, dd->fail_read_on_bb);
 	else
-		r = dust_map_write(dd, bio->bi_iter.bi_sector, dd->fail_read_on_bb);
+		r = dust_map_write(dd, dust_sector, dd->fail_read_on_bb);
 
 	return r;
 }
@@ -415,7 +415,7 @@ static int dust_message(struct dm_target *ti, unsigned int argc, char **argv,
 			char *result, unsigned int maxlen)
 {
 	struct dust_device *dd = ti->private;
-	sector_t size = bdev_nr_sectors(dd->dev->bdev);
+	sector_t size = dm_sector_div_up(ti->len, dd->sect_per_block);
 	bool invalid_msg = false;
 	int r = -EINVAL;
 	unsigned long long tmp, block;
@@ -462,8 +462,7 @@ static int dust_message(struct dm_target *ti, unsigned int argc, char **argv,
 			return r;
 
 		block = tmp;
-		sector_div(size, dd->sect_per_block);
-		if (block > size) {
+		if (block >= size) {
 			DMERR("selected block value out of range");
 			return r;
 		}
@@ -490,8 +489,7 @@ static int dust_message(struct dm_target *ti, unsigned int argc, char **argv,
 			return r;
 		}
 		wr_fail_cnt = tmp_ui;
-		sector_div(size, dd->sect_per_block);
-		if (block > size) {
+		if (block >= size) {
 			DMERR("selected block value out of range");
 			return r;
 		}
-- 
2.43.0