On 17/04/2020 18:04, Theodore Y. Ts'o wrote: > What sort of reordering can take place due to I/O schedulers and or > racing write appends from different CPU's? Is it purely the > userspace's responsibility to avoid racings writes to a particular > zone? For normal writes (i.e.: REQ_OP_WRITE) the zone will be locked by the I/O scheduler (namely mq-deadline as it's currently the one which does have support for zoned block devices). For REQ_OP_ZONE_APPEND we have a trylock scheme in the SCSI emulation of ZONE_APPEND, which is fine, as SCSI disks are single queue only. A scenario that can of cause happen is concurring REQ_OP_ZONE_APPEND writes from different CPUs to the same zone. This is fine *iff* the sum of all writes stays within the free space of the zone. If one if the writes will cross a zone boundary it'll get EIO, obviously. For "userspace's responsibility", I'd re-phrase this as "a consumer's responsibility", as we don't have an interface which aims at user-space yet. The only consumer this series implements is zonefs, although we did have an AIO implementation for early testing and io_uring shouldn't be too hard to implement.
