Golang libvirt guest-agent is not available

php editor Youzi found that recently some users reported that they encountered unavailability problems when using libvirt guest-agent in Golang. libvirt guest-agent is part of the libvirt library and is used to communicate with the guest operating system in a virtual machine. However, some users have experienced connectivity issues or functionality glitches when trying to use it. This is a frustrating issue for developers who rely on libvirt guest-agent for virtual machine management and monitoring. Next, we'll explore possible causes and solutions to help resolve this issue.

Question content

I am trying to communicate with a guest agent on a qemu instance via the libvirt golang api. However, it always refuses my connection to

2022-12-02t00:10:43.799+0100    dpanic  test/main.go:335    failed to connect to guest  {"error": "virerror(code=86, domain=10, message='guest agent is not responding: qemu guest agent is not connected')"}

Even if the qemu instance is fully started and the guest agent is accessible via the command line

sudo virsh qemu-agent-command test-vm '{"execute":"guest-info"}'

Is this a bug in the implementation or do I have to register the proxy somewhere in the go code? I can't find a reference in the documentation.

    <channel type='unix'>
      <source mode='bind' path='/var/lib/libvirt/qemu/channel/target/domain-6-test-vm/org.qemu.guest_agent.0'/>
      <target type='virtio' name='org.qemu.guest_agent.0' state='connected'/>
      <alias name='channel0'/>
      <address type='virtio-serial' controller='0' bus='0' port='1'/>
    </channel>

Thanks!

Solution

I don’t know what the final reason is. I have a loop and am accessing, or more specifically, trying to access a proxy. I changed it to use a timeout of 500ms but it didn't work.

type qemuStatusResponse struct {
    Return struct {
        Exitcode int    `json:"exitcode,omitempty"`
        OutData  string `json:"out-data,omitempty"`
        Exited   bool   `json:"exited,omitempty"`
        ErrData  string `json:"err-data,omitempty"`
    } `json:"return,omitempty"`
}

func (l *LibvirtInstance) waitForCompletion(ctx context.Context, pid int, domain *libvirt.Domain) (response *qemuStatusResponse, err error) {
    response = &qemuStatusResponse{}

    ticker := time.NewTicker(500 * time.Millisecond)
    defer ticker.Stop()
    for {
        select {
        case <-ticker.C:
            result, err := domain.QemuAgentCommand(
                fmt.Sprintf(`
                {
                    "execute": "guest-exec-status",
                    "arguments": {
                        "pid": %d
                    }
                    }`, pid),
                libvirt.DOMAIN_QEMU_AGENT_COMMAND_BLOCK, 0)
            if err != nil {
                return nil, err
            }
            if err := json.Unmarshal([]byte(result), response); err != nil {
                return nil, err
            }
            if response.Return.Exited {
                return response, nil
            }
        case <-ctx.Done():
            return nil, ctx.Err()
        }
    }
}

Additionally, I encountered some stability issues (i.e. when multiple concurrent requests were made to the connection, it would sometimes get corrupted). I found some articles online suggesting adding users to the kvm group. This works for me.

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