cli: --disk: Add driver.metadata_cache options

Properly setting the metadata cache size can provide better performance
in case of using big qcow2 images.

This patch introduces two driver options:
* driver.metadata_cache.max_size
* driver.metadata_cache.max_size.unit

E.g. --disk ...,driver.type=qcow2,\
     driver.metadata_cache.max_size=2,\
     driver.metadata_cache.max_size.unit=MiB

BTW, Metadata cache size control is currently supported only for qcow2.
Regarding how to properly caluclate the cache size of qcow2, Please refer
to qemu's documentation.

Signed-off-by: Lin Ma <lma@suse.com>

tests/data/cli/compare/virt-install-many-devices.xml

@@ -423,6 +423,15 @@
       </source>
       <target dev="vdu" bus="virtio"/>
     </disk>
+    <disk type="file" device="disk">
+      <driver name="qemu" type="qcow2">
+        <metadata_cache>
+          <max_size unit="KiB">2048</max_size>
+        </metadata_cache>
+      </driver>
+      <source file="/tmp/disk1.qcow2"/>
+      <target dev="vdv" bus="virtio"/>
+    </disk>
     <controller type="usb" index="0" model="ich9-ehci1">
       <address type="pci" domain="0" bus="0" slot="4" function="7"/>
     </controller>

tests/test_cli.py

@@ -605,6 +605,7 @@ source.reservations.managed=no,source.reservations.source.type=unix,source.reser
 --disk path=/fooroot.img,size=.0001,transient=on
 --disk source.dir=/
 --disk type=nvme,source.type=pci,source.managed=no,source.namespace=2,source.address.domain=0x0001,source.address.bus=0x02,source.address.slot=0x00,source.address.function=0x0
+--disk /tmp/disk1.qcow2,size=16,driver.type=qcow2,driver.metadata_cache.max_size=2048,driver.metadata_cache.max_size.unit=KiB
 
 
 --network user,mac=12:34:56:78:11:22,portgroup=foo,link_state=down,rom_bar=on,rom_file=/tmp/foo

virtinst/cli.py

@@ -3497,6 +3497,8 @@ class ParserDisk(VirtCLIParser):
         "driver.io": "io",
         "driver.name": "driver_name",
         "driver.type": "driver_type",
+        "driver.metadata_cache.max_size": "metadata_cache.max_size",
+        "driver.metadata_cache.max_size.unit": "metadata_cache.max_size.unit",
     }
 
     def _add_advertised_aliases(self):
@@ -3696,6 +3698,11 @@ class ParserDisk(VirtCLIParser):
         cls.add_arg("driver.queues", "driver_queues")
         cls.add_arg("driver.error_policy", "error_policy")
 
+        cls.add_arg("driver.metadata_cache.max_size",
+                    "driver_metadata_cache_max_size")
+        cls.add_arg("driver.metadata_cache.max_size.unit",
+                    "driver_metadata_cache_max_size_unit")
+
         cls.add_arg("iotune.read_bytes_sec", "iotune_rbs")
         cls.add_arg("iotune.write_bytes_sec", "iotune_wbs")
         cls.add_arg("iotune.total_bytes_sec", "iotune_tbs")

virtinst/devices/disk.py

@@ -481,6 +481,11 @@ class DeviceDisk(Device):
     driver_iothread = XMLProperty("./driver/@iothread", is_int=True)
     driver_queues = XMLProperty("./driver/@queues", is_int=True)
 
+    driver_metadata_cache_max_size = XMLProperty(
+        "./driver/metadata_cache/max_size", is_int=True)
+    driver_metadata_cache_max_size_unit = XMLProperty(
+        "./driver/metadata_cache/max_size/@unit")
+
     error_policy = XMLProperty("./driver/@error_policy")
     serial = XMLProperty("./serial")
     wwn = XMLProperty("./wwn")