Re: [libvirt-users] [libvirt] Add support for vhost-user-scsi-pci/vhost-user-blk-pci

Cole Robinson <crobinso(a)redhat.com&gt; 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(a)redhat.com&gt; 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