在 6/30/2025 11:57 PM, Mikulas Patocka 写道:
On Mon, 23 Jun 2025, Dongsheng Yang wrote:+static int dm_pcache_map_bio(struct dm_target *ti, struct bio *bio) +{ + struct pcache_request *pcache_req = dm_per_bio_data(bio, sizeof(struct pcache_request)); + struct dm_pcache *pcache = ti->private; + int ret; + + pcache_req->pcache = pcache; + kref_init(&pcache_req->ref); + pcache_req->ret = 0; + pcache_req->bio = bio; + pcache_req->off = (u64)bio->bi_iter.bi_sector << SECTOR_SHIFT; + pcache_req->data_len = bio->bi_iter.bi_size; + INIT_LIST_HEAD(&pcache_req->list_node); + bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector); This looks suspicious because you store the original bi_sector to pcache_req->off and then subtract the target offset from it. Shouldn't "bio->bi_iter.bi_sector = dm_target_offset(ti, bio->bi_iter.bi_sector);" be before "pcache_req->off = (u64)bio->bi_iter.bi_sector << SECTOR_SHIFT;"? Yes, that logic is indeed questionable, but it works in testing. Since we define dm-pcache as a **singleton**, both behaviors should effectively be equivalent, IIUC. Also, in V1 I moved the call to `dm_target_offset()` so it runs before setting up `pcache_req->off`, making the code logic correct.If this target is singleton, you can delete the call to dm_target_offset at all. That call is harmless, but it looks confusing when reviewing the code, because pcache_req->off is set to the absolute bio sector (from the start of the table) and bio->bi_iter.bi_sector is set to the relative bio sector (from the start of the target). If the target always starts at offset 0, dm_target_offset just returns bi_sector.
That makes sense Thanx
Mikulas
