[libvirt] [PATCH 5/5] qemu: Use memory-backing-file only when needed

[Martin Kletzander]

We are using memory-backing-file even when it's not needed, for example
if user requests hugepages for mamory backing, but does not specify any
pagesize, neither memory node pinning.  This causes migrations to fail
when migrating from older libvirt that did not do this.  So similarly to
commit 7832fac84741d65e851dbdbfaf474785cbfdcf3c which does it for
memory-backend-ram, this commit makes is more generic and
backend-agnostic, so the backend is not used if there is no specific
pagesize of hugepages requested, no nodeset the memory node should be
bound to, no memory access change required, and so on.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1266856

Signed-off-by: Martin Kletzander <mkletzan at redhat.com>
---
 src/qemu/qemu_command.c                            | 36 ++++++++++------------
 .../qemuxml2argv-hugepages-numa.args               |  6 ++--
 2 files changed, 19 insertions(+), 23 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 321a5e931350..7ff3e535a543 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -5120,12 +5120,6 @@ qemuBuildMemoryBackendStr(unsigned long long size,
     }

     if (pagesize || hugepage) {
-        if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE)) {
-            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
-                           _("this qemu doesn't support hugepage memory backing"));
-            goto cleanup;
-        }
-
         if (pagesize) {
             /* Now lets see, if the huge page we want to use is even mounted
              * and ready to use */
@@ -5204,29 +5198,31 @@ qemuBuildMemoryBackendStr(unsigned long long size,
             goto cleanup;
     }

-    if (!hugepage && !pagesize) {
-
-        if ((userNodeset || nodeSpecified || force) &&
-            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_RAM)) {
+    /* If none of the following is requested... */
+    if (!pagesize && !userNodeset && !memAccess && !nodeSpecified && !force) {
+        /* report back that using the new backend is not necessary
+         * to achieve the desired configuration */
+        ret = 1;
+    } else {
+        /* otherwise check the required capability */
+        if (STREQ(*backendType, "memory-backend-file") &&
+            !virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE)) {
             virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
                            _("this qemu doesn't support the "
-                             "memory-backend-ram object"));
+                             "memory-backend-file object"));
             goto cleanup;
+        } else if (STREQ(*backendType, "memory-backend-ram") &&
+                   !virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_RAM)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("this qemu doesn't support the "
+                             "memory-backend-ram object"));
         }

-        /* report back that using the new backend is not necessary to achieve
-         * the desired configuration */
-        if (!userNodeset && !nodeSpecified) {
-            *backendProps = props;
-            props = NULL;
-            ret = 1;
-            goto cleanup;
-        }
+        ret = 0;
     }

     *backendProps = props;
     props = NULL;
-    ret = 0;

  cleanup:
     virJSONValueFree(props);
diff --git a/tests/qemuxml2argvdata/qemuxml2argv-hugepages-numa.args b/tests/qemuxml2argvdata/qemuxml2argv-hugepages-numa.args
index 37511b109b6e..3496cf1a732d 100644
--- a/tests/qemuxml2argvdata/qemuxml2argv-hugepages-numa.args
+++ b/tests/qemuxml2argvdata/qemuxml2argv-hugepages-numa.args
@@ -4,9 +4,9 @@ LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=spice \
 -M pc-i440fx-2.3 \
 -m size=1048576k,slots=16,maxmem=1099511627776k \
 -smp 2 \
--object memory-backend-file,id=ram-node0,prealloc=yes,\
-mem-path=/dev/hugepages2M/libvirt/qemu,size=1073741824 \
--numa node,nodeid=0,cpus=0-1,memdev=ram-node0 \
+-mem-prealloc \
+-mem-path /dev/hugepages2M/libvirt/qemu \
+-numa node,nodeid=0,cpus=0-1,mem=1024 \
 -object memory-backend-file,id=memdimm0,prealloc=yes,\
 mem-path=/dev/hugepages1G/libvirt/qemu,size=1073741824,host-nodes=1-3,policy=bind \
 -device pc-dimm,node=0,memdev=memdimm0,id=dimm0 \
-- 
2.6.0