On Tue, Nov 23, 2021 at 11:39:11AM +0000, Johannes Thumshirn wrote: > I think we have to differentiate two cases here: > A "regular" REQ_OP_ZONE_APPEND bio and a RAID stripe REQ_OP_ZONE_APPEND > bio. The 1st one (i.e. the regular REQ_OP_ZONE_APPEND bio) can't be split > because we cannot guarantee the order the device writes the data to disk. > For the RAID stripe bio we can split it into the two (or more) parts that > will end up on _different_ devices. All we need to do is a) ensure it > doesn't cross the device's zone append limit and b) clamp all > bi_iter.bi_sector down to the start of the target zone, a.k.a sticking to > the rules of REQ_OP_ZONE_APPEND. Exactly. A stacking driver must never split a REQ_OP_ZONE_APPEND bio. But the file system itself can of course split it as long as each split off bio has it's own bi_end_io handler to record where it has been written to.
