On Fri, Dec 23, 2011 at 09:36:23AM +0100, Paolo Bonzini wrote: > Here is a revised version of the virtio-scsi proposal. There's actually > not too much left intact from v1. :) The devil is in the details, but I think I broadly agree with everything suggested in the proposal below. > The main simplification is in how SCSI hosts can be addressed in a stable > manner. > > > SCSI controller models > ====================== > > Existing controller models are "auto", "buslogic", "lsilogic", "lsias1068", > or "vmpvscsi". The new controller model "virtio-scsi" is added. The model > "lsilogic" is mapped to the existing "lsi" device in QEMU. > > When PPC64 support will be added, another controller model "spapr-vscsi" > will be added. > > > Stable addressing for SCSI devices > ================================== > > The existing <address type='drive' ...> element will be extended as follows: > > <address type='drive' controller='...' > bus='...' target='...' unit='...'/> > > where controller selects the qdev parent device, while bus/target/unit > are passed as qdev properties (the QEMU names are respectively channel, > scsi-id, lun). > > Libvirt should check for the QEMU "scsi-disk.channel" property. If it > is unavailable, QEMU will only support channel=lun=0 and 0<=target<=7. > > > LUN passthrough: block devices > ============================== > > A SCSI block device from the host can be attached to a domain in two > ways: as an emulated LUN with SCSI commands implemented within QEMU, > or by passing SCSI commands down to the block device. The former is > handled by the existing <disk type='file'>, <disk type='block'> and > <disk type='network'> XML syntax. The latter is not yet supported. > > On the QEMU side, LUN passthrough is implemented by one of the > scsi-generic and scsi-block devices. Scsi-generic requires a /dev/sg > device name, and can be applied to any device. scsi-block is only > available in QEMU 1.0 or newer, requires a block device, can be applied > only to block devices (sd/sr) and has better performance. > > To implement LUN passthrough for block device, libvirt will add a new > <disk device='lun'> attribute. When, device='lun' is passed, the device > attribute is ignored. > > Example: > > <disk type='block' device='lun'> > <disk name='qemu' type='raw'/> > <source dev='/dev/sda'/> > <target dev='sda' bus='scsi'> > <address type='drive' controller='...' > bus='...' target='...' unit='...'/> > </disk> > > Also, virtio-blk handling will be enhanced to disable SG_IO passthrough > when <disk device='disk'>, and only enable it when <disk device='lun'>. > > (I am not sure whether the 'lun' value should be for the type or device > attribute. Laine has a patch to implement it for virtio disks which > uses "type"). If you consider today we have type=block type=file type=network any of these 3 can be fronted by a virtio-blk device in the guest which allows SG_IO. With type='file' SG_IO is trivially blocked. We have initially focused on type=block, presuming that type=network doesn't support SG_IO either. Thus we were free to suggest a new type=lun to replace type=block without getting into an ambiguity. In retrospect I don't think this presumption is valid. I think it is conceivable that type=network could support SG_IO when pointed to QEMU's userspace iSCSI block driver. Thus I think we need to rather use device=lun, as suggested in this proposal > > This syntax makes it clear what is the passed-through device, and at > the same time it makes it very easy to switch a disk between emulated > and passthrough modes. Also, a stable addressing for the source device > is provided by /dev/disk/by-id and /dev/disk/by-path. > > > Stable SCSI host addressing > =========================== > > SCSI host number in Linux is not stable. An alternative stable > addressing is required to pass a whole host or target to a guest. > > One place in which this could be supported is the SCSI volume pool > syntax: > > <pool type='scsi'> > <name>virtimages</name> > <source> > <adapter name='host0'/> > </source> > <target> > <path>/dev/disk/by-id</path> > </target> > </pool> > > libvirt will deprecate the above form for the adapter element and > provide the following forms: > > <adapter name='scsi_host0'/> > > <adapter parent='pci_0000_00_1f_2' unique_id='1'/> > > The existing form changes from host0 to scsi_host0, for > consistency with the naming that is used in nodedev. The new > parent/unique_id addressing uses a parent PCI device and a unique > id that Linux provides in sysfs. In order to determine the SCSI > host number, libvirt would scan all files matched by the glob pattern > /sys/bus/pci/devices/0000:00:1f.2/*/scsi_host/*/unique_id, looking for > the one that contains "1". > > The unique_id can be omitted. In this case, the pool will refer > to the host with the smallest unique_id under the given device. > > Furthermore, a SCSI pool can be restricted to one target using an > additional element: > > <source> > <adapter name='scsi_host0'/> > <address type='scsi' bus='0' target='0'/> > </source> > > (bus defaults to 0, target is mandatory). > > > Generic passthrough > =================== > > Generic device passthrough at the LUN, target or host level builds > on the extensions to SCSI addressing from the previous section. > > Passing a single LUN extends the <hostdev> tag as follows: > > <hostdev type='scsi'> > <source> > <adapter name='scsi_host0'/> > <address type='scsi' bus='0' target='0' unit='0'/> > </source> > <target> > <address type='scsi' controller='...' > bus='...' target='...' unit='...'/> > </target> > </hostdev> > > This will map to a -drive QEMU option referring to a scsi-generic > device, and a "-device scsi-generic" option referring to the drive. > libvirt can determine the /dev/sg file to use by reading the directory > /sys/bus/scsi/devices/target*/*/scsi_generic. These devices might also > be shown in the nodedev tree, similar to block devices. > > Whenever a domain should receive all devices belonging to a SCSI host, > a similar <source> item should be included within the <controller > type='scsi'> element: > > <controller type='scsi' model='virtio-scsi'> > <source> > <adapter name='scsi_host0'/> > </source> > </controller> > > In this case, libvirt should use scsi-block rather than scsi-generic > for block devices. > > > NPIV-based SCSI host passthrough > ================================ > > In NPIV, a virtual HBA is created using "virsh nodedev-create" and passed > to the guest. Passing through a whole SCSI host is quite common when > using NPIV. As a result, it is desirable to easily address virtual HBAs > both in SCSI storage pools and in <controller type='scsi'> elements. > > Here are two proposals for how to refer to NPIV adapters: > > 1) add persistent nodedevs via commands nodedev-define, nodedev-undefine, > nodedev-start. The persistent nodedevs have a name, and this can be > used simply with <adapter name='NAME'>. > > 2) Virtual adapters do have a stable address, namely its WWN. This > can be used in a third <adapter> syntax: > > <source> > <adapter type='fc_host' wwpn='...' wwnn='...'/> > </source> Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list