FYI there's some more recent discussion over here: https://www.redhat.com/archives/libvir-list/2019-December/msg00817.html There isn't any objections to using <disk type='vhostuser'/> for vhost-user-blk, so maybe that's a good place to start. Thanks, Cole On 10/15/19 7:34 AM, Li Feng wrote: > Cole Robinson <crobinso@xxxxxxxxxx> 于2019年10月15日周二 上午1:48写道： >> >> On 10/14/19 3:12 AM, Li Feng wrote: >>> Hi Cole & Michal, >>> >>> I'm sorry for my late response, I just end my journey today. >>> Thank your response, your suggestion is very helpful to me. >>> >>> I have added Michal in this mail, Michal helps me review my initial patchset. >>> (https://www.spinics.net/linux/fedora/libvir/msg191339.html) >>> >> >> Whoops I missed that posting, I didn't realize you had sent patches! >> >>> All concern about this feature is the XML design. >>> My original XML design exposes more details of Qemu. >>> >>> <vhost-user-blk-pci type='unix'> >>> <source type='bind' path='/tmp/vhost-blk.sock'> >>> <reconnect enabled='yes' timeout='5' /> >>> </source> >>> <queue num='4'/> >>> </vhost-user-blk-pci> >>> >>> As Cole's suggestion, the better design with all vhost-user-scsi/blk >>> features would like this: >>> >>> vhost-user-blk: >>> >>> <disk type='vhostuser' device='disk'> >>> <source type='unix' path='/path/to/vhost-user-blk.sock' mode='client'> >>> <reconnect enabled='yes' timeout='5' /> >>> </source> >>> <target dev='vda' bus='virtio'/> >>> <queue num='4'/> >>> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' function='0x0'/> >>> </disk> >>> >>> vhost-user-scsi: >>> >>> <disk type='vhostuser' device='disk'> >>> <source type='unix' path='/path/to/vhost-user-scsi.sock' mode='client'> >>> <reconnect enabled='yes' timeout='5' /> >>> </source> >>> <target dev='sda' bus='scsi'/> >>> <queue num='4'/> >>> </disk> >>> >> >> I think my SCSI idea is wrong, sorry. vhost-user-scsi is for passing a >> scsi host adapter to the VM, correct? If so, then it's not really a >> <disk>, and so using the existing vhost-scsi support in <hostdev> is >> probably better. <hostdev> could possible be used for vhost-user-blk as well >> >> Can you provide some examples of full qemu command lines using >> vhost-user-blk and vhost-user-scsi? Just linking to examples else where >> is fine, but I'm wondering if there's more context > > You could check the vhost-user-scsi/blk examples from SPDK pages: > https://spdk.io/doc/vhost.html > >> >> Internally we already have an abstraction for vhost-scsi: >> >> <hostdev mode='subsystem' type='scsi_host'> >> <source protocol='vhost' wwpn='XXX'/> >> </hostdev> >> >> >> The obvious extension would be >> >> <hostdev mode='subsystem' type='scsi_host'> >> <source protocol='vhostuser' type='unix' >> path='/path/to/vhost-user-scsi.sock' mode='client'/> >> </hostdev> >> >> Internally implementing this will be weird. The <source> parameters are >> only dictated by the hostdev type= field, but in this case they would be >> dictated by the <source protocol=> field, and we would want to reuse the >> internal chardev abstraction. >> >> vhost-user-blk could be implemented similarly, but with type='storage' >> which is the way we pass through block devices to LXC guests, but it >> isn't currently supported in the qemu driver. >> >> I dunno. Maybe Michal or danpb can provide guidance >> > @Michal, @danpb, could you give some guidance? >> >>> Conclusion: >>> 1. Add new type(vhostuser) for disk label; >>> 2. Add queue sub-label for disk to support multiqueue(<queue >>> num='4'/>) or reusing the driver label >>> (<driver name='vhostuser' queues='4'), which one is better? >>> Qemu support multiqueue like this: >>> -device vhost-user-scsi-pci,id=scsi0,chardev=spdk_vhost_scsi0,num_queues=4 >>> -device vhost-user-blk-pci,chardev=spdk_vhost_blk0,num-queues=4 >>> >> >> num-queues is already supported by libvirt for both <disk> and <hostdev> >> with <driver queues=X/>, so whether we use <disk> or <hostdev> you won't >> need to add any new XML here. > Got it. > >> >>> Another question: >>> When qemu is connecting to a vhost-user-scsi controller[1], there may >>> exist multiple LUNs under one target, >>> then one disklabel(<disk/>) will represent multiple SCSI LUNs, >>> the 'dev' property(<target dev='sda' bus='scsi'/>) will be ignored, right? >>> In other words, for vhost-user-scsi disk, it more likes a controller, >>> maybe the controller label is suitable. >>> >> >> Yes you are right, and this was my understanding. But then its not >> really a <controller> in libvirt's sense because we can't attach >> emulated devices to it, so it's more a fit for the existing <hostdev> >> vhost-user support. Unfortunately it's not really a clean fit anywhere, >> there will have to be some kind of compromise. And I'm not sure if >> <disk> or <hostdev> is right for vhost-user-blk, but hopefully others >> have more clear opinions. > > I'm also confused about it. > Thanks for your reply. > > Thanks, > Feng Li > >> >> Thanks, >> Cole >> >>> I look forward to hearing from you as soon as possible. >>> >>> [1]: https://spdk.io/doc/vhost.html >>> >>> Feng Li >>> >>> Cole Robinson <crobinso@xxxxxxxxxx> 于2019年10月10日周四 上午6:48写道： >>>> >>>> Sorry for the late reply, and thanks Jano for pointing out elsewhere >>>> that this didn't receive a response. >>>> >>>> On 8/12/19 5:56 AM, Li Feng wrote: >>>>> Hi Guys, >>>>> >>>>> And I want to add the vhost-user-scsi-pci/vhost-user-blk-pci support >>>>> for libvirt. >>>>> >>>>> The usage in qemu like this: >>>>> >>>>> Vhost-SCSI >>>>> -chardev socket,id=char0,path=/var/tmp/vhost.0 >>>>> -device vhost-user-scsi-pci,id=scsi0,chardev=char0 >>>>> Vhost-BLK >>>>> -chardev socket,id=char1,path=/var/tmp/vhost.1 >>>>> -device vhost-user-blk-pci,id=blk0,chardev=char1 >>>>> >>>> >>>> Indeed that matches what I see for the qemu commits too: >>>> >>>> https://git.qemu.org/?p=qemu.git;a=commit;h=00343e4b54b >>>> https://git.qemu.org/?p=qemu.git;a=commit;h=f12c1ebddf7 >>>> >>>>> What type should I add for libvirt. >>>>> Type1: >>>>> <hostdev mode='subsystem' type='vhost-user'> >>>>> <source protocol='vhost-user-scsi' path='/tmp/vhost-scsi.sock'></source> >>>>> <alias name="vhost-user-scsi-disk1"/> >>>>> </hostdev> >>>>> >>>>> >>>>> Type2: >>>>> >>>>> <disk type='network' device='disk'> >>>>> <driver name='qemu' type='raw' cache='none' io='native'/> >>>>> <source protocol='vhost-user' path='/tmp/vhost-scsi.sock'> >>>>> </source> >>>>> <target dev='sdb' bus='vhost-user-scsi'/> >>>>> <boot order='3'/> >>>>> <alias name='scsi0-0-0-1'/> >>>>> <address type='drive' controller='0' bus='0' target='0' unit='1'/> >>>>> </disk> >>>>> >>>>> >>>>> <disk type='network' device='disk'> >>>>> <driver name='qemu' type='raw' cache='none' io='native'/> >>>>> <source protocol='vhost-user' path='/tmp/vhost-blk.sock'> >>>>> </source> >>>>> <target dev='vda' bus='vhost-user-blk'/> >>>>> <boot order='1'/> >>>>> <alias name='virtio-disk0'/> >>>>> <address type='pci' domain='0x0000' bus='0x00' slot='0x07' >>>>> function='0x0'/> >>>>> </disk> >>>>> >>>> >>>> I think wiring this into <disk> makes more sense. <hostdev> is really an >>>> abstraction for assigning a (typically) physical host device to the VM, >>>> so it handles things like hiding a PCI device from the host, and passing >>>> that exact device to the VM. >>>> >>>> In the vhost-user-scsi/blk case, the host device is just a special >>>> process running on the other side of a socket, and the device >>>> represented to the guest is a typical virtio device. So to me it makes >>>> more sense as a <disk> with a <source> that points at that socket. >>>> >>>> target bus=virtio vs bus=scsi is already used to distinguish between >>>> virtio-blk and virtio-scsi, so I think we can keep that bit as is, with >>>> the <address type=drive|pci> to match. We just need to differentiate >>>> between plain virtio and vhost-user >>>> >>>> network devices already have vhostuser support: >>>> >>>> <interface type='vhostuser'> >>>> <source type='unix' path='/tmp/vhost1.sock' mode='server|client'/> >>>> <model type='virtio'/> >>>> </interface> >>>> >>>> Internally that <source> is a virDomainChrSourceDefPtr which is our >>>> internal representation of a chardev. So I think something akin to this >>>> is the way to go. It will likely require updating a LOT of places in the >>>> code that check disk type= field, probably most places that care about >>>> whether type=NETWORK or type=!NETWORK will need to be mirrored for the >>>> new type. >>>> >>>> <disk type='vhostuser' device='disk'> >>>> <source type='unix' path='/path/to/vhost-user-blk.sock' mode='client'/> >>>> <target dev='vda' bus='virtio'/> >>>> </disk> >>>> >>>> <disk type='vhostuser' device='disk'> >>>> <source type='unix' path='/path/to/vhost-user-scsi.sock' mode='client'/> >>>> <target dev='sda' bus='scsi'/> >>>> </disk> >>>> >>>> - Cole >>> >> >> >> - Cole > - Cole -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
