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Re: [Qemu-devel] [RFC PATCH v2 0/8] s390x: Enable virtio-scsi boot from


From: Cornelia Huck
Subject: Re: [Qemu-devel] [RFC PATCH v2 0/8] s390x: Enable virtio-scsi boot from /dev/sgX
Date: Wed, 17 May 2017 13:48:41 +0200

On Tue, 16 May 2017 15:44:43 +0200
Christian Borntraeger <address@hidden> wrote:

> On 05/10/2017 05:53 PM, Eric Farman wrote:
> > Today, trying to boot a guest from a SCSI LUN on s390x yields the following:
> > 
> >   virtio-blk               = OK
> >   virtio-scsi and /dev/sdX = OK
> >   virtio-scsi and /dev/sgX = FAIL
> > 
> > Example of the failing scenario:
> > 
> >   /usr/bin/qemu-system-s390x ...
> >     -device virtio-scsi-ccw,id=scsi0,devno=fe.0.0001
> >     -drive file=/dev/sg2,if=none,id=drive0,format=raw
> >     -device 
> > scsi-generic,bus=scsi0.0,channel=0,scsi-id=0,drive=drive0,id=disk0
> >   LOADPARM=[........]
> >   Using virtio-scsi.
> >   Using SCSI scheme.
> >   ..
> >   ! virtio-scsi:read_many: STATUS=02 RSPN=70 KEY=0b CODE=00 QLFR=06, sure !
> > 
> > Why do we care?  Well, libvirt converts a virtio-scsi device from the host
> > SCSI address (host:bus:target:lun) into the associated /dev/sgX device,
> > which means we can't boot from virtio-scsi and have to rely on virtio-blk
> > for this action.
> > 
> > The short version of what happens is the host block 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 1-3 read the max_sectors parameter for the virtio-scsi controller,
> > and break up the READ(10) I/Os into something that the host will accept.
> > If not specified, max_sectors defaults to 65535, but could look like this:
> > 
> >   qemu-system-s390x ...
> >     -device virtio-scsi-ccw,id=scsi0,devno=fe.0.0001,max_sectors=2048
> > 
> > Patches 4-6 read the max_io_size parameter for the virtio-scsi disk device,
> > and use the minimum of it and the max_sectors from the controller for 
> > breaking
> > up the READ(10) I/Os.  If not specified, max_io_size defaults to 2147483647
> > but could look like this:
> > 
> >   qemu-system-s390x ...
> >     -drive file=/dev/sda,if=none,id=drive0,format=raw ...
> >     -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,
> >             drive=drive0,id=disk0,max_io_size=1048576
> > 
> > In the two examples above, the maximum parameters are equivalent due to the
> > controller parameter measuring 512-byte blocks, and the disk measuring 
> > bytes.
> > 
> > Patch 7 establishes a workable default, in case neither the controller nor
> > the disk have the parameters specified (and thus the overly large defaults
> > are taken), or if they are set to something beyond what we can boot from.
> > 
> > Patch 8 rebuilds the s390-ccw BIOS with this entire patch set.
> > 
> > Changelog:
> > 
> > RFC v2:
> >  - Dropped patch outside the pc-bios/s390-ccw/ tree
> >  - Added Christian's r-b to patch 1 (formerly patch 2)
> >  - Added EVPD Inquiry calls to retrieve Block Limits page if supported
> >  - Added a default if Block Limits page is not supported, or response is
> >    still way to big to allow boot
> > RFC v1:
> >  - https://lists.nongnu.org/archive/html/qemu-devel/2017-04/msg05121.html
> > 
> > Eric Farman (8):
> >   pc-bios/s390-ccw: Remove duplicate blk_factor adjustment
> >   pc-bios/s390-ccw: Move SCSI block factor to outer read
> >   pc-bios/s390-ccw: Break up virtio-scsi read into multiples
> >   pc-bios/s390-ccw: Refactor scsi_inquiry function
> >   pc-bios/s390-ccw: Get list of supported VPD pages
> >   pc-bios/s390-ccw: Get Block Limits VPD device data
> >   pc-bios/s390-ccw: Build a reasonable max_sectors limit
> >   pc-bios/s390-ccw.img: rebuild image
> > 
> >  pc-bios/s390-ccw.img           | Bin 26472 -> 26480 bytes
> >  pc-bios/s390-ccw/s390-ccw.h    |   7 ++++
> >  pc-bios/s390-ccw/scsi.h        |  30 +++++++++++++++
> >  pc-bios/s390-ccw/virtio-scsi.c |  85 
> > +++++++++++++++++++++++++++++++++++------
> >  pc-bios/s390-ccw/virtio-scsi.h |   2 +
> >  pc-bios/s390-ccw/virtio.h      |   1 +
> >  6 files changed, 114 insertions(+), 11 deletions(-)
> > 
> 
> Patch set looks good. Conny, can you apply the series?
> 

I had hoped for some comments from folks more familiar with scsi...

Nevertheless, applied to s390-next.




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