From: Robin Dong <sanbai@xxxxxxxxxx> We are now trying to modify flashcache(https://github.com/facebook/flashcache) to make it request based so that we can let cfq io-controller control the bandwidth between different io cgroups. A search in the dm directory tells me that only multipath is a request based dm target and its functionality is very simple and map_rq() is used to map the request to different underlying devices. We can't work in this way because: 1. the request which processed by map_rq() need to be issued to different lower devices (disk device and cache device, in flashcache), therefore the request can't be totally remapped by simply changing its queue and returning DM_MAPIO_REMAPPED in map_rq() like multipath_map() 2. to submit bios drectly in map_rq() (by return DM_MAPIO_SUBMITTED) will cause BUG_ON(!irqs_disabled()) in dm_request_fn() because the submit_bio()->generic_make_request()->blk_queue_bio() will definitly call spin_unlock_irq to enable the irqs As above,the interface map_rq() provided by devcie-mapper framework is not enough for an autonomous target, like flashcache. We propose to add a new mk_rq interface so that we can make the requests by ourselves. Signed-off-by: Robin Dong <sanbai@xxxxxxxxxx> --- drivers/md/dm.c | 10 ++++++++++ include/linux/device-mapper.h | 3 +++ 2 files changed, 13 insertions(+), 0 deletions(-) diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 4e09b6f..3ae67de 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1459,11 +1459,21 @@ static int dm_request_based(struct mapped_device *md) static void dm_request(struct request_queue *q, struct bio *bio) { struct mapped_device *md = q->queuedata; + struct dm_table *map = dm_get_live_table(md); + struct dm_target *ti = dm_table_find_target(map, bio->bi_sector); + + if (ti->type->mk_rq) { + ti->type->mk_rq(ti, q, bio); + goto out; + } if (dm_request_based(md)) blk_queue_bio(q, bio); else _dm_request(q, bio); + +out: + dm_table_put(map); } void dm_dispatch_request(struct request *rq) diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h index 38d27a1..2386389 100644 --- a/include/linux/device-mapper.h +++ b/include/linux/device-mapper.h @@ -50,6 +50,8 @@ typedef int (*dm_map_fn) (struct dm_target *ti, struct bio *bio, union map_info *map_context); typedef int (*dm_map_request_fn) (struct dm_target *ti, struct request *clone, union map_info *map_context); +typedef int (*dm_make_request_fn) (struct dm_target *ti, + struct request_queue *q, struct bio *bio); /* * Returns: @@ -136,6 +138,7 @@ struct target_type { dm_dtr_fn dtr; dm_map_fn map; dm_map_request_fn map_rq; + dm_make_request_fn mk_rq; dm_endio_fn end_io; dm_request_endio_fn rq_end_io; dm_presuspend_fn presuspend; -- 1.7.1 -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
