On 05/05/2017 18:12, Eric Farman wrote: > > > On 05/05/2017 11:13 AM, Paolo Bonzini wrote: >> >> >> On 05/05/2017 17:03, Eric Farman wrote: >>> We get a value of x3fffff when sending that to a scsi-disk from bios >>> code. That's fully emulated though, in scsi_disk_emulate_inquiry. And >>> that's the scenario that already works. >>> >>> While there is indeed code in hw/scsi/scsi-generic.c to wire that in, >>> that only happens after the I/O goes to the device itself. The Block >>> Limits page isn't supported [1] and thus it gets rejected with "invalid >>> field in cdb". We never get to that fixup code you reference, since the >>> returned len is zero. >>> >>> Should I be refactoring this code to always patch in that block limit >>> regardless of a response from the host/device? (That is, when page xb0 >>> isn't supported by the hw.) >> >> What is the BLKSECTGET value you get? > > x140000 bytes when using /dev/sg0 (xa00 sectors when using /dev/sda). > >> Is there a sensible default value >> that you can use when page 0xb0 isn't supported by the hardware? > > I was setting max_sectors to x800 with good success, which was the > power-of-2 floor that BLKSECTGET gave us. That kept us within the > limits of the host biovec code. But it's a long way from the > virtio-scsi value of xFFFF when max_sectors isn't specified, so don't > know what side effects that may cause.
It's just slower, but 0x800 is already a megabyte worth of data so it's not going to be that much slower. Paolo
