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How to hot plugin a new vhost-user-blk-pci device to running VM?
by Liang Chaojun 13 May '21

13 May '21

Hi Guy, Does anyone clear how to hot plugin a new vhost-user-blk-pci device to a running VM? Before staring vm , I pass the disk through QEMU command line like below. <qemu:commandline> <qemu:arg value='-object'/> <qemu:arg value='memory-backend-file,id=mem0,size=4G,mem-path=/dev/hugepages,share=on'/> <qemu:arg value='-numa'/> <qemu:arg value='node,memdev=mem0'/> <qemu:arg value='-chardev'/> <qemu:arg value='socket,id=spdk_vhost_blk721ea46a-b306-11eb-a280-525400a98761,path=/var/tmp/vhost.721ea46a-b306-11eb-a280-525400a98761,reconnect=1'/> <qemu:arg value='-device'/> <qemu:arg value='vhost-user-blk-pci,chardev=spdk_vhost_blk721ea46a-b306-11eb-a280-525400a98761,bootindex=1,num-queues=4'/> <qemu:arg value='-chardev'/> <qemu:arg value='socket,id=spdk_vhost_blk2f699c58-d222-4629-9fdc-400c3aadc55e,path=/var/tmp/vhost.2f699c58-d222-4629-9fdc-400c3aadc55e,reconnect=1'/> <qemu:arg value='-device'/> <qemu:arg value='vhost-user-blk-pci,chardev=spdk_vhost_blk2f699c58-d222-4629-9fdc-400c3aadc55e,num-queues=4'/> </qemu:commandline> But I don’t know how to live add a vhost-user-blk-pci device on running VM even with calling attachDevice API now. OS: redhat 7.4 Libvirt version: 3.4 Your help will be appreciated. Thanks!

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boot arm64 guest stuck
by Jiatong Shen 11 May '21

11 May '21

hello community, I am stuck at a problem where a virtual machine stuck at "guest has not initialized the display" on a arm64 (FT2000+) server and the relevant qemu process will continue to have a cpu usage of 100%. I do try with different qemu and qemu-efi combined and found out that if I use qemu build qemu-system-arm/now 1:2.11+dfsg-1ubuntu7.15~cloud1 arm64 with qemu-efi/now 0~20160408.ffea0a2c-2 all and set gic-version to 2, the vm could boot. the virtual machine uses a kylink 4.0 image. I am scrubbing my head to debug the bug and find out the reason... any idea or advice will be appreciated. thank you very much for the help -- Best Regards, Jiatong Shen

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trying to understand how libvirt uses firewalld
by Felix Schwarz 30 Apr '21

30 Apr '21

Hi, I recently installed a test box using CentOS 8 and installed a CentOS 8 guest via libvirt (KVM). I need to use "routed" forwarding as the datacenter only gives me individual IPs which are routed to the physical interface and the switch only accepts packets with a well-known MAC address. On the host I enabled firewalld and moved the guest to a specific firewalld zone. I verified that libvirt is detecting firewalld. My idea was that I could use this to create somewhat fine-grained filters on the host for traffic from the internet to the guest (and possibly vice-versa). However it seems like that does not work the way I wanted: It seems as if nothing changes when I allow/disallow SSH for that zone. I can still ssh from the internet to the guest. After several reads on the documentation I have a guess of what might be going on but I'd like to confirm that: https://libvirt.org/firewall.html#fw-firewalld-and-virtual-network-driver > If firewalld is active on the host, libvirt will attempt to place the bridge > interface of a libvirt virtual network into the firewalld zone named > "libvirt" (thus making all guest->host traffic on that network subject to > the rules of the "libvirt" zone). Does that mean libvirt's firewalld usage is ONLY for traffic guest->host and does not affect all other traffic (e.g. host->guest, guest<->internet)? That sounds incredibly narrow (and not very useful for me) but it would explain why I don't see any effects in my experiment... --- In a related note it would be nice if there was a way to make routed setups with individual IPs easier. This problem hunts me for more than 10 years (I think I posted something in 2009 - still the same problem basically) and it would be nice if libvirt could somehow support this use case better: I want to allow traffic guest <-> internet in a routed setup. libvirt generates iptables rules like these: Chain LIBVIRT_FWO (1 references) pkts bytes target prot opt in out source destination 0 0 ACCEPT all -- br-private * 10.11.0.0/24 0.0.0.0/0 0 0 REJECT all -- br-private * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable 0 0 ACCEPT all -- br-public * (NETWORK IP ) 0.0.0.0/0 43 3232 REJECT all -- br-public * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-port-unreachable I my case "NETWORK IP" is a /32 IPv4 and AFAIK I have to put the host's IPv4 here (which is basically the router) so I can assign the guest IP inside the VM. What I need is basically a rule like ACCEPT one above but with the GUEST IP. I have some elaborate Python script which I can use as a "network" hook but that requires parsing output of "iptables" due to libvirt's events (e.g. libvirtd restart triggers one "plugged" event per VM). Thank you very much, Felix

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l3 cache and cpu pinning
by Roman Mohr 24 Apr '21

24 Apr '21

Hi, I have a question regarding enabling l3 cache emulation on Domains. Can this also be enabled without cpu-pinning, or does it need cpu pinning to emulate the l3 caches according to the cpus where the guest is pinned to? Thank you and best regards, Roman

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GlusterFS pools - do they work?
by lejeczek 22 Apr '21

22 Apr '21

Hi guys. I've been a consumer of libvirt for a while but this is first time I'm trying this: -> $ virsh vol-create-as glusterfs-VMs2 fcos-node1.qcow2 20G --format qcow2 error: Failed to create vol fcos-node1.qcow2 error: this function is not supported by the connection driver: storage pool does not support volume creation I'm on CentOS Stream with glusterfs-8.4, libvirt-7 and qemu-kvm-5.2.0 What might be the issue here? many thanks, L.

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external snapshot create error
by Eyüp Hakan Duran 21 Apr '21

21 Apr '21

Dear all, I have been creating external snapshots of my KVM/QEMU VMs for more than a year on a host machine that runs Manjaro Linux. The current version of libvirt I am using is 1:7.1.0-3. I just noticed that the script I am using for this purpose has been failing. More specifically the command below returns with the error message indicated underneath the command: sudo virsh snapshot-create-as --no-metadata --domain myVM myVM-state --diskspec hda,file=overlay.qcow2 --disk-only --atomic error: XML document failed to validate against schema: Unable to validate doc against /usr/share/libvirt/schemas/domainsnapshot.rng Extra element disks in interleave Element domainsnapshot failed to validate content I also tried different versions of the command above with similar results, such as: sudo virsh snapshot-create-as mvVM --no-metadata myVM-state --diskspec hda,snapshot=external,file=overlay.qcow2 --disk-only --atomic Any pointers will be greatly appreciated! Hakan Duran

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could not start libvirt service
by shafnamol N 15 Apr '21

15 Apr '21

Hi, I am using *CentOS 8*. I have built *libvirt* with the following method: $ meson build -Dsystem=true $ ninja -C build $ ninja -C build install But the problem is when i started it # systemctl start libvirtd Job for libvirtd.service failed because the control process exited with error code. See "systemctl status libvirtd.service" and "journalctl -xe" for details. i tried to get the status of libvirt # systemctl status libvirtd libvirtd.service - Virtualization daemon Loaded: loaded (/usr/lib/systemd/system/libvirtd.service; enabled; vendor preset: enabled) Active: failed (Result: exit-code) What will be the problem? Thanks for the help in advanc....

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Confusion over networking configuration - I might be able to do some documentation
by Ed B 13 Apr '21

13 Apr '21

Hi libvirt users, I have been using libvirt on Debian Linux for a few months. (Mostly with virt-manager. I haven't yet learned all of the command line commands.) I'm currently confused by bridge mode networking, which I think is what I require to address the particular use case, which I will describe: My use case: Prior to this I have been using routed mode to organize my VMs. Most of the VMs I deploy are for services (web servers, mail servers, etc) so I require them to have static IP addresses on my local network. ==== An aside / comment: I *can* set those static IPs using the command line virsh net-edit (from memory) command and then change the settings in the xml files. However, since this seems like something that many users would require regularly it would be nice to be able to set static IP in the GUI when configuring with virt-manager. I assume that the same people who maintain libvirt also maintain virt-manager? If I'm wrong please re-direct me. Returning to the main discussion: It would be more convenient for me personally if I were able to set the IP addresses of these VMs using static addresses configured via an external DHCP server. I believe I can do this if my network is in "bridge" mode instead of NAT or Routed. I know this should be possible from reading information online but there doesn't seem to be any option for this in the virt-manager GUI. ==== To give more details on my setup: My network has a pfsense instance which is able to provide IP addresses to local machines. I would like to use the same pfsense machine to provide IP addresses to virtual machines. If I am not mistaken, the only way to do this would be to bridge the network on which the VMs reside to the network on which the pfsense machine resides. I will provide some screenshots to illustrate my confusion. When creating a new virtual network, I assume that I do not want to enable DHCPv4, because I want the pfsense system to allocate IP addresses. I do not know whether I should leave "Enable ipv4 network address space definition" or what the value should be. See image below. [cid:4e926d97-7a58-4350-93cc-0db7c401c075] Further in the setup (step 4), I assume I need to choose "Forward to physical network" rather than "Isolated virtual network". For the destination option, I do not know what should be chosen. I don't fully understand how this option works. For "Mode" there are three options: NAT, Routed and finally "Open". I cannot find any documentation which indicates what "Open" means. NAT and Routed are clearly not the correct options here - by a process of elimination that would imply that "Open" means "bridged" but I have a feeling that this is incorrect and I don't understand something else. Again, see screengrab below. [cid:f2ea4e34-c418-48d3-86b2-d7ff1002990a] I am quite keen to contribute something to documentation. At the moment I don't understand enough about how libvirt works to be able to do this. Apologies if my questions have been directed to the wrong people. If this is the case could you please re-direct me to the right place to ask such questions? Best regards

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move mount permission denied
by Jiatong Shen 12 Apr '21

12 Apr '21

Hello community! I am faced with a mysterious [error]( https://gist.github.com/jshen28/5f29eed51e0a1308684214b35f009478) which says move mount is not permissioned. We are using libvirt with openstack-helm which running libvirt in a docker based k8s environment. /dev/termination-log is a device created and attached by k8s and mount looks like `/dev/mapper/ubuntu--vg-root on /var/log/termination-log type ext4 (rw,relatime,errors=remount-ro,data=ordered)` Any idea why this happens? appreciate the help! -- Best Regards, Jiatong Shen

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how to use external snapshots with memory state
by Riccardo Ravaioli 12 Apr '21

12 Apr '21

Hi all, Best wishes for 2021! :) So I've been reading and playing around with live snapshots and still haven't figured out how to use an external memory snapshot. My goal is to take a disk+memory snapshot of a running VM and, if possible, save it in external files. As far as I understand, I can run: $ virsh snapshot-create $VM ... and that'll take an *internal* live snapshot of a given VM, consisting of its disks and memory state, which will be stored in the qcow2 disk(s) of the VM. In particular, the memory state will be stored in the first disk of the VM. I can then use the full range of snapshot commands available: revert, list, current, delete. Now, an external snapshot can be taken with: $ virsh snapshot-create-as --domain $VM mysnapshot --diskspec vda,file=/home/riccardo/disk_mysnapshot.qcow2,snapshot=external --memspec file=/home/riccardo/mem_mysnapshot.qcow2,snapshot=external ... with as many "--diskspec" as there are disks in the VM. I've read the virsh manual and the libvirt API documentation, but it's not clear to me what exactly I can do then with an external snapshot, in particular with the file containing the memory state. In articles from 7-8 years ago people state that external memory snapshots cannot be reverted... is it still the case today? If so, what's a typical usage for such files? If not with libvirt, is it possible to revert to an external memory + disk state in other ways, for instance through qemu commands? Thanks! Riccardo

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