[Libguestfs] [PATCH 3/3] launch-libvirt: add virtio-net via the standard <interface> element

[Laszlo Ersek]

Starting with version 3.8.0, libvirt allows us to specify the network
address and network mask (as prefix) for SLIRP directly via the
<interface> element in the domain XML:
<https://libvirt.org/formatdomain.html#userspace-slirp-stack>. This means
we don't need the <qemu:commandline> hack for virtio-net on such versions.

Restrict the hack in construct_libvirt_xml_qemu_cmdline() to
libvirt<3.8.0, and generate the proper <interface> element in
construct_libvirt_xml_devices() on libvirt>=3.8.0.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2034160
Suggested-by: Richard W.M. Jones <rjones at redhat.com>
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---

Notes:
    v1:
    
    - Tested with "virt-rescue --network" and "ping", using the "libvirt"
      back-end, after setting "net.ipv4.ping_group_range" properly in sysctl
      on the host. (Libvirt version: libvirt-daemon-7.6.0-3.fc35.x86_64.)
    
    - The generated libvirt XML, per "virsh dumpxml", contains
    
        <devices>
          <interface type='user'>
            <mac address='52:54:00:fe:23:48'/>
            <ip address='169.254.0.0' family='ipv4' prefix='16'/>
            <model type='virtio'/>
            <alias name='net0'/>
            <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
          </interface>
        </devices>
        <qemu:commandline>
          <qemu:env name='TMPDIR' value='/home/lacos/src/v2v/guestfs-tools/tmp'/>
        </qemu:commandline>
    
      and the consequent QEMU cmdline has
    
        -netdev user,net=169.254.0.0/16,id=hostnet0 \
        -device virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:fe:23:48,bus=pci.0,addr=0x2 \
    
    - The full set of PCI addresses that libvirt assigns to the virtio
      devices are, per "virsh dumpxml":
    
        <controller type='scsi' index='0' model='virtio-scsi'>
          <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    
        <controller type='virtio-serial' index='0'>
          <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    
        <interface type='user'>
          <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    
        <rng model='virtio'>
          <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    
    - The same, verified with
    
        virsh -c ... qemu-monitor-command guestfs-... --hmp info qtree
    
      is:
    
        bus: main-system-bus
          dev: i440FX-pcihost, id ""
            bus: pci.0
              dev: virtio-rng-pci, id "rng0"
                addr = 05.0
              dev: virtio-net-pci, id "net0"
                addr = 02.0
              dev: virtio-serial-pci, id "virtio-serial0"
                addr = 04.0
              dev: virtio-scsi-pci, id "scsi0"
                addr = 03.0

 lib/guestfs-internal.h |  3 ++-
 lib/launch-libvirt.c   | 27 +++++++++++++++++++++++++--
 2 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/lib/guestfs-internal.h b/lib/guestfs-internal.h
index e24d570f5aa7..4a19e5c6bb47 100644
--- a/lib/guestfs-internal.h
+++ b/lib/guestfs-internal.h
@@ -173,7 +173,8 @@ cleanup_mutex_unlock (pthread_mutex_t **ptr)
 #endif
 
 /* Place the virtio-net controller in slot 0x1e on the root bus, on normal
- * hardware with PCI. Refer to RHBZ#2034160.
+ * hardware with PCI. Necessary only before libvirt 3.8.0. Refer to
+ * RHBZ#2034160.
  */
 #ifdef HAVE_LIBVIRT_BACKEND
 #if defined(__arm__) || defined(__s390x__)
diff --git a/lib/launch-libvirt.c b/lib/launch-libvirt.c
index 266d88824686..cc714c02efbf 100644
--- a/lib/launch-libvirt.c
+++ b/lib/launch-libvirt.c
@@ -1413,6 +1413,28 @@ construct_libvirt_xml_devices (guestfs_h *g,
       } end_element ();
     } end_element ();
 
+    /* Virtio-net NIC with SLIRP (= userspace) back-end, if networking is
+     * enabled. Starting with libvirt 3.8.0, we can specify the network address
+     * and prefix for SLIRP in the domain XML. Therefore, we can add the NIC
+     * via the standard <interface> element rather than <qemu:commandline>, and
+     * so libvirt can manage the PCI address of the virtio-net NIC like the PCI
+     * addresses of all other devices. Refer to RHBZ#2034160.
+     */
+    if (g->enable_network &&
+        guestfs_int_version_ge (&params->data->libvirt_version, 3, 8, 0)) {
+      start_element ("interface") {
+        attribute ("type", "user");
+        start_element ("model") {
+          attribute ("type", "virtio");
+        } end_element ();
+        start_element ("ip") {
+          attribute ("family", "ipv4");
+          attribute ("address", NETWORK_ADDRESS);
+          attribute ("prefix", NETWORK_PREFIX);
+        } end_element ();
+      } end_element ();
+    }
+
     /* Libvirt adds some devices by default.  Indicate to libvirt
      * that we don't want them.
      */
@@ -1835,9 +1857,10 @@ construct_libvirt_xml_qemu_cmdline (guestfs_h *g,
     } end_element ();
 
     /* Workaround because libvirt user networking cannot specify "net="
-     * parameter.
+     * parameter. Necessary only before libvirt 3.8.0; refer to RHBZ#2034160.
      */
-    if (g->enable_network) {
+    if (g->enable_network &&
+        !guestfs_int_version_ge (&params->data->libvirt_version, 3, 8, 0)) {
       start_element ("qemu:arg") {
         attribute ("value", "-netdev");
       } end_element ();
-- 
2.19.1.3.g30247aa5d201