[libvirt] [PATCH v2 7/7] qemu: Format 'write-cache' parameter for disk frontends

[Peter Krempa]

The disk cache mode translates to various frontend and backend
attributes for the qemu block layer. For the frontend device the
'writeback' parameter is used and provided as 'write-cache'. Implement
this so that we can later switch to using -blockdev where we will not
pass the cachemode directly any more.

Signed-off-by: Peter Krempa <pkrempa at redhat.com>
---
 src/qemu/qemu_command.c                            | 27 ++++++++++++++++++++++
 .../disk-drive-write-cache.new.args                | 10 ++++----
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c
index a1a9e91e49..08c6e4faac 100644
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@@ -1822,6 +1822,30 @@ qemuCheckIOThreads(const virDomainDef *def,
 }


+static int
+qemuBuildDriveDevCacheStr(virDomainDiskDefPtr disk,
+                          virBufferPtr buf,
+                          virQEMUCapsPtr qemuCaps)
+{
+    bool wb;
+
+    if (disk->cachemode == VIR_DOMAIN_DISK_CACHE_DEFAULT)
+        return 0;
+
+    if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_DISK_WRITE_CACHE))
+        return 0;
+
+    if (qemuDomainDiskCachemodeFlags(disk->cachemode, &wb, NULL, NULL) < 0)
+        return -1;
+
+    virBufferStrcat(buf, ",write-cache=",
+                    virTristateSwitchTypeToString(virTristateSwitchFromBool(wb)),
+                    NULL);
+
+    return 0;
+}
+
+
 char *
 qemuBuildDriveDevStr(const virDomainDef *def,
                      virDomainDiskDefPtr disk,
@@ -2134,6 +2158,9 @@ qemuBuildDriveDevStr(const virDomainDef *def,
         }
     }

+    if (qemuBuildDriveDevCacheStr(disk, &opt, qemuCaps) < 0)
+        goto error;
+
     if (virBufferCheckError(&opt) < 0)
         goto error;

diff --git a/tests/qemuxml2argvdata/disk-drive-write-cache.new.args b/tests/qemuxml2argvdata/disk-drive-write-cache.new.args
index 90414a100f..3973249d18 100644
--- a/tests/qemuxml2argvdata/disk-drive-write-cache.new.args
+++ b/tests/qemuxml2argvdata/disk-drive-write-cache.new.args
@@ -28,16 +28,18 @@ server,nowait \
 -device lsi,id=scsi0,bus=pci.0,addr=0x2 \
 -drive file=/dev/HostVG/QEMUGuest1,format=qcow2,if=none,id=drive-ide0-0-0,\
 cache=writeback \
--device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1 \
+-device ide-hd,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0,bootindex=1,\
+write-cache=on \
 -drive file=/dev/HostVG/QEMUGuest1,format=qcow2,if=none,id=drive-scsi0-0-0,\
 cache=none \
--device scsi-hd,bus=scsi0.0,scsi-id=0,drive=drive-scsi0-0-0,id=scsi0-0-0 \
+-device scsi-hd,bus=scsi0.0,scsi-id=0,drive=drive-scsi0-0-0,id=scsi0-0-0,\
+write-cache=on \
 -drive file=/dev/HostVG/QEMUGuest1,format=qcow2,if=none,id=drive-virtio-disk0,\
 cache=writethrough \
 -device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x3,drive=drive-virtio-disk0,\
-id=virtio-disk0 \
+id=virtio-disk0,write-cache=off \
 -drive file=/dev/HostVG/QEMUGuest1,format=qcow2,if=none,id=drive-usb-disk1,\
 cache=directsync \
 -device usb-storage,bus=usb.0,port=1,drive=drive-usb-disk1,id=usb-disk1,\
-removable=off \
+removable=off,write-cache=off \
 -msg timestamp=on
-- 
2.16.2