add libvirt nodeinfo datasource

[memetb]

This feature allows querying the host machine's nodeinfo through the libvirt protocol.

This is useful for, among other things, obtaining the target machine's architecture to select a guest image.

// main.tf
provider "libvirt" {
  uri = "qemu+ssh://${var.target}/system?sshauth=privkey&no_verify"
}

data "libvirt_nodeinfo" "host" {}

locals {
  arch = data.libvirt_nodeinfo.host.arch
  images = {
    "debian-x86_64" = "/srv/images/debian-12-backports-generic-amd64.qcow2",
    "debian-aarch64"  = "/srv/images/debian-12-backports-generic-arm64.qcow2",
  }
  image_path = local.images["debian-${local.arch}"]
}

output image_path {
  value = local.image_path
}

Which will create the following output:

$~/terraform-provider-libvirt/testing$ TF_VAR_target=chromium terraform apply 
data.libvirt_nodeinfo.host: Reading...
data.libvirt_nodeinfo.host: Read complete after 1s [id=d4e1bf70-6374-45b7-a970-fb584a1b4062]

Changes to Outputs:
  + image_path = "/srv/images/debian-12-backports-generic-arm64.qcow2"

You can apply this plan to save these new output values to the Terraform state, without changing any real infrastructure.

Do you want to perform these actions?
  Terraform will perform the actions described above.
  Only 'yes' will be accepted to approve.

  Enter a value: yes


Apply complete! Resources: 0 added, 0 changed, 0 destroyed.

Outputs:

image_path = "/srv/images/debian-12-backports-generic-arm64.qcow2"
$~/terraform-provider-libvirt/testing$ terraform show 
# data.libvirt_nodeinfo.host:
data "libvirt_nodeinfo" "host" {
    arch                      = "aarch64"
    cores                     = 2
    dies                      = 1
    features                  = [
        "fp",
        "asimd",
        "evtstrm",
        "aes",
        "pmull",
        "sha1",
        "sha2",
        "crc32",
        "cpuid",
    ]
    host                      = "qemu+ssh://chromium/system?sshauth=privkey&no_verify=true"
    id                        = "d4e1bf70-6374-45b7-a970-fb584a1b4062"
    live_migration_support    = true
    live_migration_transports = [
        "tcp",
        "rdma",
    ]
    model                     = "cortex-a72"
    sockets                   = 1
    threads                   = 1
    topology                  = []
    vendor                    = "ARM"
}


Outputs:

image_path = "/srv/images/debian-12-backports-generic-arm64.qcow2"

[memetb]

My bad, this appears to have been merged in #1042 - after I started the feature, before I pushed this PR.

[memetb]

I've made this a draft until the issue #1074 is discussed