On 05/05/2017 03:41 AM, Fam Zheng wrote:
On Wed, 04/26 16:46, Eric Farman wrote:
The short version of what happens is the host device driver rejects our
requests because the transfer lengths are too long for it to satisfy.
A virtio-scsi disk connected via scsi-generic is fine as a non-boot device
because the guest kernel is able to break up the requests for us. So we just
need to handle this situation for the boot process.
Patches 2-N in this series do that, but rely on us to specify the max_sectors
parameter for the virtio-scsi-ccw device:
/usr/bin/qemu-system-s390x ...
-device virtio-scsi-ccw,id=scsi0,devno=fe.0.0001,max_sectors=2048
Can you instead do an INQUIRY from the bios code to check the Block Limits page?
The response is intercepted by hw/scsi/scsi-generic.c to merge in the host LUN's
limits. That's how Linux kernel finds the granularity for request splitting.
It's a good idea (Thanks Christian, Paolo, and Fam :), but this leads to
other difficulties.
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.)
- Eric
[1] If I issue an EVPD page x00 from the QEMU bios code, I only see
pages xb1, xc0, and c1 are supported. If I look at the supported pages
from the host, I see a few more but still not xb0:
$ sg_inq --page=0 /dev/sda
VPD INQUIRY: Supported VPD pages page
Supported VPD pages:
0x0 Supported VPD pages
0x80 Unit serial number
0x83 Device identification
0x86 Extended INQUIRY data
0xb1 Block device characteristics (sbc3)
0xc0 vendor: Firmware numbers (seagate); Unit path report (EMC)
0xc1 vendor: Date code (seagate)
$ sg_inq --page=0 /dev/sg0
VPD INQUIRY: Supported VPD pages page
Supported VPD pages:
0x0 Supported VPD pages
0x80 Unit serial number
0x83 Device identification
0x86 Extended INQUIRY data
0xb1 Block device characteristics (sbc3)
0xc0 vendor: Firmware numbers (seagate); Unit path report (EMC)
0xc1 vendor: Date code (seagate)
That way, patch 1 is not necessary too. I don't like it because it doesn't
always work considering LUN hotplug.
Fam
