Kiyoshi Ueda wrote: > This patch enables request-based dm. > > o Request-based dm and bio-based dm coexist, since there are > some target drivers which are more fitting to bio-based dm. > Also, there are other bio-based devices in the kernel > (e.g. md, loop). > Since bio-based device can't receive struct request, > there are some limitations on device stacking between > bio-based and request-based. > > type of underlying device > bio-based requeset-based > ---------------------------------------------- > bio-based OK OK > request-based NG OK > > The device type is recognized by the queue flag in the kernel, > so dm follows that. > > o The type of a dm device is decided at the first table binding time. > Once the type of a dm device is decided, the type can't be changed. > > o Mempool allocations are deferred to at the table loading time, since > mempools for request-based dm are different from those for bio-based > dm and needed mempool type is fixed by the type of table. > > o Currently, request-based dm supports only tables that have a single > target. To support multiple targets, we need to support request > splitting or prevent bio/request from spanning multiple targets. > The former needs lots of changes in the block layer, and the latter > needs that all target drivers support merge() function. > Both will take a time. > > > Signed-off-by: Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx> > Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx> Acked-by: Hannes Reinecke <hare@xxxxxxx> Cheers, Hannes -- Dr. Hannes Reinecke zSeries & Storage hare@xxxxxxx +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: Markus Rex, HRB 16746 (AG Nürnberg) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
