qemu: Check for drop-cache capability

QEMU 4.0.0 and newer automatically drops caches at the end of migration.
Let's check for this capability so that we can allow migration when disk
cache is turned on.
Signed-off-by: NJiri Denemark <jdenemar@redhat.com>
Acked-By: NPeter Krempa <pkrempa@redhat.com>

src/qemu/qemu_capabilities.c

@@ -536,6 +536,7 @@ VIR_ENUM_IMPL(virQEMUCaps,
 
               /* 335 */
               "bochs-display",
+              "migration-file-drop-cache",
     );
 
 
@@ -1279,6 +1280,7 @@ static struct virQEMUCapsStringFlags virQEMUCapsQMPSchemaQueries[] = {
     { "query-iothreads/ret-type/poll-max-ns", QEMU_CAPS_IOTHREAD_POLLING },
     { "query-display-options/ret-type/+egl-headless/rendernode", QEMU_CAPS_EGL_HEADLESS_RENDERNODE },
     { "nbd-server-add/arg-type/bitmap", QEMU_CAPS_NBD_BITMAP },
+    { "blockdev-add/arg-type/+file/drop-cache", QEMU_CAPS_MIGRATION_FILE_DROP_CACHE },
 };
 
 typedef struct _virQEMUCapsObjectTypeProps virQEMUCapsObjectTypeProps;

src/qemu/qemu_capabilities.h

@@ -517,6 +517,7 @@ typedef enum { /* virQEMUCapsFlags grouping marker for syntax-check */
 
     /* 335 */
     QEMU_CAPS_DEVICE_BOCHS_DISPLAY, /* -device bochs-display */
+    QEMU_CAPS_MIGRATION_FILE_DROP_CACHE, /* migration with disk cache on is safe for type='file' disks */
 
     QEMU_CAPS_LAST /* this must always be the last item */
 } virQEMUCapsFlags;

tests/qemucapabilitiesdata/caps_4.0.0.aarch64.xml

@@ -164,6 +164,7 @@
   <flag name='bitmap-merge'/>
   <flag name='nbd-bitmap'/>
   <flag name='bochs-display'/>
+  <flag name='migration-file-drop-cache'/>
   <version>4000000</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>61700758</microcodeVersion>

tests/qemucapabilitiesdata/caps_4.0.0.ppc64.xml

@@ -169,6 +169,7 @@
   <flag name='bitmap-merge'/>
   <flag name='nbd-bitmap'/>
   <flag name='bochs-display'/>
+  <flag name='migration-file-drop-cache'/>
   <version>4000000</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>42900758</microcodeVersion>

tests/qemucapabilitiesdata/caps_4.0.0.riscv32.xml

@@ -167,6 +167,7 @@
   <flag name='bitmap-merge'/>
   <flag name='nbd-bitmap'/>
   <flag name='bochs-display'/>
+  <flag name='migration-file-drop-cache'/>
   <version>4000000</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>0</microcodeVersion>

tests/qemucapabilitiesdata/caps_4.0.0.riscv64.xml

@@ -167,6 +167,7 @@
   <flag name='bitmap-merge'/>
   <flag name='nbd-bitmap'/>
   <flag name='bochs-display'/>
+  <flag name='migration-file-drop-cache'/>
   <version>4000000</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>0</microcodeVersion>

tests/qemucapabilitiesdata/caps_4.0.0.s390x.xml

@@ -131,6 +131,7 @@
   <flag name='query-current-machine'/>
   <flag name='bitmap-merge'/>
   <flag name='nbd-bitmap'/>
+  <flag name='migration-file-drop-cache'/>
   <version>4000000</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>39100758</microcodeVersion>

tests/qemucapabilitiesdata/caps_4.0.0.x86_64.xml

@@ -206,6 +206,7 @@
   <flag name='nbd-bitmap'/>
   <flag name='x86-max-cpu'/>
   <flag name='bochs-display'/>
+  <flag name='migration-file-drop-cache'/>
   <version>4000000</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>43100758</microcodeVersion>

tests/qemucapabilitiesdata/caps_4.1.0.x86_64.xml

@@ -208,6 +208,7 @@
   <flag name='cpu-unavailable-features'/>
   <flag name='canonical-cpu-features'/>
   <flag name='bochs-display'/>
+  <flag name='migration-file-drop-cache'/>
   <version>4000050</version>
   <kvmVersion>0</kvmVersion>
   <microcodeVersion>43100759</microcodeVersion>