[PATCH v2 5/5] qemu: Enable memory-backend-file.discard-data whenever possible

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

https://bugzilla.redhat.com/show_bug.cgi?id=1480668

The cases when we cannot enable this optimization are:
  1) nvdimms
  2) if memAccess='shared'

Otherwise it is safe to enable it.

Signed-off-by: Michal Privoznik <mprivozn@xxxxxxxxxx>
---
 src/qemu/qemu_command.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index 527a35779d..b920f5c3e4 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -3121,6 +3121,13 @@ qemuBuildMemoryBackendStr(virJSONValuePtr *backendProps,
                                   NULL) < 0)
             goto cleanup;
 
+        if (!mem->nvdimmPath && memAccess != VIR_DOMAIN_MEMORY_ACCESS_SHARED &&
+            virQEMUCapsGet(qemuCaps, QEMU_CAPS_OBJECT_MEMORY_FILE_DISCARD) &&
+            virJSONValueObjectAdd(props,
+                                  "B:discard-data", true,
+                                  NULL) < 0)
+            goto cleanup;
+
         switch (memAccess) {
         case VIR_DOMAIN_MEMORY_ACCESS_SHARED:
             if (virJSONValueObjectAdd(props, "b:share", true, NULL) < 0)
-- 
2.16.1

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