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how to change emulator path during live migration
by Jiatong Shen 27 Apr '22

27 Apr '22

Hello libvirt experts, I am facing the following exceptions during live migrating a virtual machine from one compute node to another. file or directory: libvirt.libvirtError: Cannot check QEMU binary /usr/bin/kvm-spice: No such file or directory File "/var/lib/openstack/lib/python3.6/site-packages/eventlet/tpool.py", line 83, in tworker rv = meth(*args, **kwargs) File "/var/lib/openstack/lib/python3.6/site-packages/libvirt.py", line 1745, in migrateToURI3 if ret == -1: raise libvirtError ('virDomainMigrateToURI3() failed', dom=self) libvirt.libvirtError: Cannot check QEMU binary /usr/bin/kvm-spice: No such file or directory After some investigation, we found that this error is triggered because we do not have qemu-kvm installed in our container, btw the libvirt is directly installed on the source node. I have following questions Is it possible to change emulator during live migration? I try to to remove emulator under devices but looks like it does not help. thank you very much and looking forward for the feedback. -- Best Regards, Jiatong Shen

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set fixed time at vm guest startup?
by Fred Clift 26 Apr '22

26 Apr '22

I'm looking at the <clock> libvirt parameters. Is there a way to set the guests clock to a specific time/date at virt startup? I'm trying to virtualize a system with pci passthrough for a hardware device that wants to always live in pre-2011. The license manager for the software/hardware has 31-bit overflow of time calculations. The current process on the physical machine is to power it on, use the bios to set the hardware date to Jan 1 2010, boot the system, use an RC script to ntp-set the date now that the hardware is up and running, and then everything works till next boot. We even have a nice rc script that will set the clock back to 2010 if you do a clean shutdown/reboot. I see I can set my clock sync to variable and specify a negative offset - is there a way to just say "always be jan 10 2010 when you power on"? Fred

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discard option on ext4 mounts in QEMU qcow2 images
by Nate Collins 25 Apr '22

25 Apr '22

Hello, Does anyone have any real-world statistics on the reliability and performance of the ext4 discard option in QEMU VMs? I've heard it's discouraged for physical devices, as some are inefficient in how TRIM requests are processed, but I was wondering if there were any drawbacks/warnings when it comes to virtual disks (in this case, QCOW2s). I currently use either virtio-scsi or virtio-blk drivers for disk images depending on what the host/guest support, and run TRIMs weekly, but having an immediate freeing of space is desirable for many reasons. Also wondering if snapshots on snapshotting filesystems (such as ZFS) can run into corruption or other issues if snapshots are taken during a TRIM. Thanks.

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race condition? virsh migrate --copy-storage-all
by Valentijn Sessink 20 Apr '22

20 Apr '22

Hi list, I'm trying to migrate a few qemu virtual machines between two 1G ethernet connected hosts, with local storage only. I got endless "error: operation failed: migration of disk vda failed: Input/output error" errors and thought: something wrong with settings. However, then, suddenly: I succeeded without changing anything. And, hey: while ! time virsh migrate --live --persistent --undefinesource --copy-storage-all ubuntu20.04 qemu+ssh://duikboot/system; do a=$(( $a + 1 )); echo $a; done ... retried 8 times, but then: success. This smells like a race condition, doesn't it? A bit weird is the fact that the migration seems to succeed every time while copying from revolving disks to SSD; but the other way around has this Input/output error. There are some messages in /var/log/syslog, but not at the time of the failure, and no disk errors. These disks are LVM2 volumes and they live on raid arrays - and/so there is not a real, as in physical, I/O-error. Source system has SSD's, target system has regular disks. 1) is this the right mailing list? I'm not 100% sure. 2) how can I research this further? Spending hours on a "while / then" loop to try and retry live migration looks like a dull job for my poor computers ;-) Best regards, Valentijn

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Virtio-scsi and block mirroring
by Bjoern Teipel 19 Apr '22

19 Apr '22

Hello everyone, I’m looking at an issue where I do see guests freezing (Dl) process state during a block disk mirror from one storage to another storage (NFS) where the network stack of the guest can freeze for up to 10 seconds. Looking at the storage and IO I noticed good throughput ad low latency <3ms and I am having trouble to track down the source for the issue, as neither storage nor networking show issues. Interestingly when I do the same test with virtio-blk I do not really see the process freezes at the frequency or duration compared to virtio-scsi which seem to indicate a client side rather than storage side problem. I had looked at the syscalls and nothing stuck out: % time seconds usecs/call calls errors syscall ------ ----------- ----------- --------- --------- ---------------- 28.51 20.672654 8339 2479 ioctl 27.81 20.162714 3379 5967 31 futex 22.02 15.964498 785 20335 poll 15.22 11.038403 150 73561 io_submit 4.17 3.023285 41 73540 lseek 1.20 0.868003 5 158591 write 0.63 0.459030 11 42871 ppoll 0.22 0.159263 8 19314 recvmsg 0.16 0.115520 5 22526 read 0.04 0.029149 29149 1 restart_syscall 0.01 0.009252 28 330 sendmsg 0.00 0.001221 1221 1 munmap 0.00 0.000458 22 21 fcntl 0.00 0.000286 95 3 openat 0.00 0.000166 5 32 rt_sigprocmask 0.00 0.000103 10 10 fdatasync 0.00 0.000099 25 4 clone 0.00 0.000081 7 12 mmap 0.00 0.000077 19 4 close 0.00 0.000076 6 12 mprotect 0.00 0.000056 14 4 madvise 0.00 0.000025 6 4 set_robust_list 0.00 0.000023 6 4 prctl ------ ----------- ----------- --------- --------- ---------------- 100.00 72.504442 419626 31 total Does anyone have an idea how to better debug this issue ? Thanks Bjoern

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When does the balloon-change or control-error event occur
by Han Han 19 Apr '22

19 Apr '22

Hi developers, I have questions about balloon-change or control-error event: 1. What's the meaning of these events 2. When do the events occur? The comments of their callbacks don't mention that( https://gitlab.com/libvirt/libvirt/-/blob/master/include/libvirt/libvirt-do… https://gitlab.com/libvirt/libvirt/-/blob/master/include/libvirt/libvirt-do… )

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Help with libvirt
by Eduardo Kiassucumuca 19 Apr '22

19 Apr '22

Good morning I'm Eduardo, a computer science student and I'm doing a final course work focused on virtualization. The work consists of creating virtual machines on a server and allowing ssh access to the virtual machines that are on the server containing qemu/kvm/libvirt. The problem is that I can't access the virtual machines from an external network but I can access them inside the server. I would like to know what would be the best way since we want to have a single public ip and be able to have a reverse proxy to access the virtual machines, I would like to know from your experience what you recommend?

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Libvirt vs QEMU benefits
by M, Shivakumar 19 Apr '22

19 Apr '22

Hello, For one of our case validation, we were using direct QEMU commands before for VM creation as it was easier to configure the VMs. Inside VM we do run the real-time latency test. Recently we switched to libvirt for the VM creation and deletion. Surprisingly, we do see a significant increase in the real-time latency performance for the VMs launched through the libvirt. W.r.t configuration wise both VMs are the same, we just converted the existing QEMU commands into libvirt XMLs. I am wondering what and all the features which libvirt has, improving this performance. Thanks, Shivakumar M

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Libvirt Daemon Question
by Michael Espinoza 13 Apr '22

13 Apr '22

Hi I’ve been googling this for a bit with no luck. Is there a way of determining what mode an already running libvirt daemon is running in.(session or system) From the docs it sounded like it was determined by what user started the daemon. But in a test node I set up, I have libvirtd running as root yet I can still connect to both the session and system qemus with virsh. And if I were to want libvirtd only in session mode, how would I do that? Thanks for the help! This stuff is really awesome and I’m just trying to get a full understanding of it. -Mike -- Michael Espinoza Mobile Phone : 646 327 9273 Email : Mikespinoza(a)gmail.com

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"default" watchdog device - ?
by lejeczek 08 Apr '22

08 Apr '22

Hi guys. Without explicitly, manually using watchdog device for a VM, the VM (centOS 8 Stream 4.18.0-365.el8.x86_64) shows '/dev/watchdog' exists. To double check - 'dumpxml' does not show any such device - what kind of a 'watchdog' that is? watchdog-5.15-2.el8.x86_64 on such a VM does not seem to do anything with it. Host is centOS 9 with: qemu-img-6.2.0-11.el9.x86_64 libvirt-daemon-8.0.0-5.el9.x86_64 many thanks, L.

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