On Thu, Nov 28, 2024 at 05:51:52PM +0900, Damien Le Moal wrote: > > Maybe. But you'll have a hard time convincing me to add any kind of > > state machine or bio matching magic to the SCSI stack when the simplest > > solution is to treat copying like a read followed by a write. There is > > no concurrency, no kernel state, no dependency between two commands, nor > > two scsi_disk/scsi_device object lifetimes to manage. > > And that also would allow supporting a fake copy offload with regular > read/write BIOs very easily, I think. So all block devices can be > presented as supporting "copy offload". That is nice for FSes. Just as when that showed up in one of the last copy offload series I'm still very critical of a stateless copy offload emulation. The reason for that is that a host based copy helper needs scratch space to read into, and doing these large allocation on every copy puts a lot of pressure onto the allocator. Allocating the buffer once at mount time and the just cycling through it is generally a lot more efficient.
