Hi, > -----Original Message----- > From: Max Reitz [mailto:mre...@redhat.com] > Sent: Friday, March 31, 2017 8:57 PM > To: Ciprian Barbu; qemu-devel@nongnu.org; Eric Blake; Alexandru Avadanii > Cc: Jeff Cody; Markus Armbruster; svc-armband; Kevin Wolf > Subject: Re: [Qemu-devel] nbd: Possible regression in 2.9 RCs > > On 31.03.2017 19:49, Ciprian Barbu wrote: > > Hi, > > > > Thank you for getting back! > > > > I'm trying to follow you, but I don't understand all the details. I would > > like to > ask this question though: > > > > What is the difference between v2.8.0 and this commit? With v2.8.0 the > same qemu command worked, but I admit it doesn't request sharing. > > The difference is that we now make sure there are for example not two > writers for the same block device (unless both agree that it's OK to have > shared writers). We haven't done that before. > > The built-in NBD server is completely OK with writes by other parties (such as > guest devices), but guest devices generally are not (because the guest OS > should know about this). > > Therefore, you'd now have to set the share-rw flag for guest devices which > should allow shared writers. Otherwise you cannot set up an NBD server on a > block device that is in use by the guest device.
Thank you for the detailed explanation! > > > We also use libvirt v1.3.4, which might be a problem, but at least we want > to understand if the commit in question introduced an obvious problem or if > it's all in the details. > > Well, I don't think there is any libvirt version that knows about this flag > yet. > > ...maybe another way to resolve the issue would be to set share-rw to true > by default for now, noting that this will be changed in the future. > In any case, I'm afraid we'll have to wait until Kevin is around on Monday. Ciprian is gone for the week-end too, so next week it is :) I think we will change the default for now in our builds, and wait for the proper support in Libvirt. Ty for the default suggestion, btw! BR, Alex > > > Btw, the qemu command generated by libvirt is this one, sorry about that: > > And sorry about not yet having thanked you for reporting this issue. :-) > > Max > > > 2017-03-31 17:40:10.956+0000: starting up libvirt version: 1.3.4, > > package: 0+amos3~u16.04 (Enea Armband Devops Team > <armb...@enea.com> > > Fri, 13 Jan 2017 02:06:05 +0100), qemu version: 2.8.50(Debian > > 1:2.9+amos2~u16.04), hostname: node-2.domain.tld LC_ALL=C > > PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin > > QEMU_AUDIO_DRV=none /usr/bin/kvm -name > > instance-00000076,debug-threads=on -S -object > > secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-14-i > > nstance-00000076/master-key.aes -machine > > virt-2.8,accel=kvm,usb=off,gic-version=3 -cpu host -m 256 -realtime > > mlock=off -smp 1,sockets=1,cores=1,threads=1 -uuid > > 2812f3c9-f564-499b-a8c7-e9e7ccf24143 -no-user-config -nodefaults - > chardev socket,id=charmonitor,path=/var/lib/libvirt/qemu/domain-14- > instance-00000076/monitor.sock,server,nowait -mon > chardev=charmonitor,id=monitor,mode=control -rtc base=utc,driftfix=slew - > no-shutdown -boot strict=on -kernel /var/lib/nova/instances/2812f3c9-f564- > 499b-a8c7-e9e7ccf24143/kernel -initrd /var/lib/nova/instances/2812f3c9- > f564-499b-a8c7-e9e7ccf24143/ramdisk -append 'root=/dev/vda1 rw rootwait > console=tty0 console=ttyS0 console=ttyAMA0' -device i82801b11- > bridge,id=pci.1,bus=pcie.0,addr=0x1 -device pci- > bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x0 -usb -drive > file=/var/lib/nova/instances/2812f3c9-f564-499b-a8c7- > e9e7ccf24143/disk,format=qcow2,if=none,id=drive-virtio- > disk0,cache=none,aio=native -device virtio-blk-device,scsi=off,drive=drive- > virtio-disk0,id=virtio-disk0,bootindex=1 -drive > file=/var/lib/nova/instances/2812f3c9-f564-499b-a8c7- > e9e7ccf24143/disk.config,format=raw,if=none,id=drive-virtio- > disk1,cache=none,aio=native -device virtio-blk-device,scsi=off,drive=drive- > virtio-disk1,id=virtio-disk1 -netdev tap,fd=27,id=hostnet0 -device virtio-net- > device,netdev=hostnet0,id=net0,mac=fa:16:3e:82:0a:2b -serial > file:/var/lib/nova/instances/2812f3c9-f564-499b-a8c7- > e9e7ccf24143/console.log -serial pty -vnc 0.0.0.0:0 -k en-us -device > VGA,id=video0,vgamem_mb=16,bus=pci.2,addr=0x1 -device virtio-balloon- > device,id=balloon0 -msg timestamp=on Domain id=14 is tainted: high- > privileges > > > > Regards, > > /Ciprian > >