[libvirt] [PATCH 3/3] qemuBuildMemoryBackendStr: Report backend requirement more appropriately

[Michal Privoznik]

So, when building the '-numa' command line, the
qemuBuildMemoryBackendStr() function does quite a lot of checks to
chose the best backend, or to check if one is in fact needed. However,
it returned that backend is needed even for this little fella:

  <numatune>
    <memory mode="strict" nodeset="0,2" />
  </numatune>

This can be guaranteed via CGroups entirely, there's no need to use
memory-backend-ram to let qemu know where to get memory from. Well, as
long as there's no <memnode/> element, which explicitly requires the
backend. Long story short, we wouldn't have to care, as qemu works
either way. However, the problem is migration (as always). Previously,
libvirt would have started qemu with:

  -numa node,memory=X

in this case and restricted memory placement in CGroups. Today, libvirt
creates more complicated command line:

  -object memory-backend-ram,id=ram-node0,size=X
  -numa node,memdev=ram-node0

Again, one wouldn't find anything wrong with these two approaches.
Both work just fine. Unless you try to migrated from the older libvirt
into the newer one. These two approaches are, unfortunately, not
compatible. My suggestion is, in order to allow users to migrate, lets
use the older approach for as long as the newer one is not needed.

Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
---
 src/qemu/qemu_command.c                                       | 6 ++++--
 tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.args     | 5 +++++
 tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.xml      | 2 +-
 tests/qemuxml2argvdata/qemuxml2argv-numatune-auto-prefer.args | 5 +++++
 tests/qemuxml2argvtest.c                                      | 5 +++++
 5 files changed, 20 insertions(+), 3 deletions(-)
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.args
 create mode 100644 tests/qemuxml2argvdata/qemuxml2argv-numatune-auto-prefer.args

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 9c25788..cbe105e 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -4699,7 +4699,9 @@ qemuBuildMemoryBackendStr(unsigned long long size,
     props = NULL;
 
     if (!hugepage) {
-        if ((nodemask || force) &&
+        bool nodeSpecified = virDomainNumatuneNodeSpecified(def->numatune, guestNode);
+
+        if ((userNodeset || nodeSpecified || force) &&
             !virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_RAM)) {
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                            _("this qemu doesn't support the "
@@ -4709,7 +4711,7 @@ qemuBuildMemoryBackendStr(unsigned long long size,
 
         /* report back that using the new backend is not necessary to achieve
          * the desired configuration */
-        if (!nodemask) {
+        if (!userNodeset && !nodeSpecified) {
             ret = 1;
             goto cleanup;
         }
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.args b/tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.args
new file mode 100644
index 0000000..481f72f
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.args
@@ -0,0 +1,5 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu-system-x86_64 -S -M pc-q35-2.3 -m 128 \
+-smp 2,maxcpus=6,sockets=6,cores=1,threads=1 \
+-nographic -monitor unix:/tmp/test-monitor,server,nowait -no-acpi \
+-boot c -net none -serial none -parallel none
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.xml b/tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.xml
index 01bbb3d..fe7c465 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.xml
+++ b/tests/qemuxml2argvdata/qemuxml2argv-cputune-numatune.xml
@@ -1,4 +1,4 @@
-<domain type='kvm'>
+<domain type='qemu'>
   <name>dummy2</name>
   <uuid>4d92ec27-9ebf-400b-ae91-20c71c647c19</uuid>
   <memory unit='KiB'>131072</memory>
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-numatune-auto-prefer.args b/tests/qemuxml2argvdata/qemuxml2argv-numatune-auto-prefer.args
new file mode 100644
index 0000000..0b1b0f5
--- /dev/null
+++ b/tests/qemuxml2argvdata/qemuxml2argv-numatune-auto-prefer.args
@@ -0,0 +1,5 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/kvm -S -M pc -m 64 -smp 1 \
+-numa node,nodeid=0,cpus=0,mem=64 \
+-nographic -monitor unix:/tmp/test-monitor,server,nowait \
+-no-acpi -boot c -usb -net none -serial none -parallel none
diff --git a/tests/qemuxml2argvtest.c b/tests/qemuxml2argvtest.c
index 2de92eb..07a581f 100644
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@@ -1260,6 +1260,9 @@ mymain(void)
     DO_TEST("cputune-zero-shares", QEMU_CAPS_NAME);
     DO_TEST_PARSE_ERROR("cputune-iothreadsched-toomuch", QEMU_CAPS_NAME);
     DO_TEST_PARSE_ERROR("cputune-vcpusched-overlap", QEMU_CAPS_NAME);
+    DO_TEST("cputune-numatune", QEMU_CAPS_SMP_TOPOLOGY,
+            QEMU_CAPS_OBJECT_MEMORY_RAM,
+            QEMU_CAPS_OBJECT_MEMORY_FILE);
 
     DO_TEST("numatune-memory", NONE);
     DO_TEST_PARSE_ERROR("numatune-memory-invalid-nodeset", NONE);
@@ -1272,6 +1275,8 @@ mymain(void)
     DO_TEST_FAILURE("numatune-memnode-no-memory", NONE);
 
     DO_TEST("numatune-auto-nodeset-invalid", NONE);
+    DO_TEST("numatune-auto-prefer", QEMU_CAPS_OBJECT_MEMORY_RAM,
+            QEMU_CAPS_OBJECT_MEMORY_FILE);
     DO_TEST_FAILURE("numatune-static-nodeset-exceed-hostnode",
                     QEMU_CAPS_OBJECT_MEMORY_RAM);
     DO_TEST_PARSE_ERROR("numatune-memnode-nocpu", NONE);
-- 
2.0.5