The options specifies metadata cache size policy for a disk.
This is going to be used only for QEMU and only for qcow2 images in
next patch to set qcow2 L2 cache size.

Signed-off-by: Nikolay Shirokovskiy <nshirokovs...@virtuozzo.com>
---
 docs/formatdomain.html.in                          | 11 ++++++
 docs/schemas/domaincommon.rng                      | 11 ++++++
 src/conf/domain_conf.c                             | 17 +++++++++
 src/conf/domain_conf.h                             |  9 +++++
 .../qemuxml2argvdata/disk-metadata_cache_size.xml  | 35 ++++++++++++++++++
 .../disk-metadata_cache_size.xml                   | 41 ++++++++++++++++++++++
 tests/qemuxml2xmltest.c                            |  2 ++
 7 files changed, 126 insertions(+)
 create mode 100644 tests/qemuxml2argvdata/disk-metadata_cache_size.xml
 create mode 100644 tests/qemuxml2xmloutdata/disk-metadata_cache_size.xml

diff --git a/docs/formatdomain.html.in b/docs/formatdomain.html.in
index 7f07bb7..fcffa9c 100644
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@@ -3608,6 +3608,17 @@
             virt queues for virtio-blk. (<span class="since">Since 
3.9.0</span>)
           </li>
           <li>
+            The optional <code>metadata_cache_size</code> attribute specifies
+            metadata cache size policy. Possible values are "default" and
+            "maximum". Using "default" leaves setting cache size to the 
hypervisor,
+            Using "maximum" ensures entire disk cache remains in memory, 
increasing
+            IO but utilizing more memory. This policy helps if workload's
+            disk working set (the amount of disk data used intensively) is too 
large
+            to be covered by cache size by "default" policy.
+            (<span class="since">Since 5.0.0, QEMU 3.0</span>). The option 
makes
+            sense only for non raw images and supported for qcow2 only now.
+          </li>
+          <li>
           For virtio disks,
           <a href="#elementsVirtio">Virtio-specific options</a> can also be
           set. (<span class="since">Since 3.5.0</span>)
diff --git a/docs/schemas/domaincommon.rng b/docs/schemas/domaincommon.rng
index aa50eac..aa8b8ff 100644
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@@ -2003,6 +2003,9 @@
         <ref name="detect_zeroes"/>
       </optional>
       <optional>
+        <ref name="metadata_cache_size"/>
+      </optional>
+      <optional>
         <attribute name='queues'>
           <ref name="positiveInteger"/>
         </attribute>
@@ -2103,6 +2106,14 @@
       </choice>
     </attribute>
   </define>
+  <define name="metadata_cache_size">
+    <attribute name='metadata_cache_size'>
+      <choice>
+        <value>default</value>
+        <value>maximum</value>
+      </choice>
+    </attribute>
+  </define>
   <define name="controller">
     <element name="controller">
       <optional>
diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
index 222bb8c..9488c35 100644
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@@ -889,6 +889,11 @@ VIR_ENUM_IMPL(virDomainDiskDetectZeroes, 
VIR_DOMAIN_DISK_DETECT_ZEROES_LAST,
               "on",
               "unmap")
 
+VIR_ENUM_IMPL(virDomainDiskMetadataCacheSize,
+              VIR_DOMAIN_DISK_METADATA_CACHE_SIZE_LAST,
+              "default",
+              "maximum")
+
 VIR_ENUM_IMPL(virDomainDiskMirrorState, VIR_DOMAIN_DISK_MIRROR_STATE_LAST,
               "none",
               "yes",
@@ -9419,6 +9424,14 @@ virDomainDiskDefDriverParseXML(virDomainDiskDefPtr def,
     }
     VIR_FREE(tmp);
 
+    if ((tmp = virXMLPropString(cur, "metadata_cache_size")) &&
+        (def->metadata_cache_size = 
virDomainDiskMetadataCacheSizeTypeFromString(tmp)) < 0) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("unknown driver metadata_cache_size value '%s'"), 
tmp);
+        goto cleanup;
+    }
+    VIR_FREE(tmp);
+
     ret = 0;
 
  cleanup:
@@ -24193,6 +24206,10 @@ virDomainDiskDefFormatDriver(virBufferPtr buf,
     if (disk->queues)
         virBufferAsprintf(&driverBuf, " queues='%u'", disk->queues);
 
+    if (disk->metadata_cache_size)
+        virBufferAsprintf(&driverBuf, " metadata_cache_size='%s'",
+                          
virDomainDiskMetadataCacheSizeTypeToString(disk->metadata_cache_size));
+
     virDomainVirtioOptionsFormat(&driverBuf, disk->virtio);
 
     return virXMLFormatElement(buf, "driver", &driverBuf, NULL);
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index fae1306..31ce9ab 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -567,6 +567,13 @@ typedef enum {
     VIR_DOMAIN_DISK_DETECT_ZEROES_LAST
 } virDomainDiskDetectZeroes;
 
+typedef enum {
+    VIR_DOMAIN_DISK_METADATA_CACHE_SIZE_DEFAULT = 0,
+    VIR_DOMAIN_DISK_METADATA_CACHE_SIZE_MAXIMUM,
+
+    VIR_DOMAIN_DISK_METADATA_CACHE_SIZE_LAST
+} virDomainDiskMetadataCacheSize;
+
 typedef struct _virDomainBlockIoTuneInfo virDomainBlockIoTuneInfo;
 struct _virDomainBlockIoTuneInfo {
     unsigned long long total_bytes_sec;
@@ -672,6 +679,7 @@ struct _virDomainDiskDef {
     int discard; /* enum virDomainDiskDiscard */
     unsigned int iothread; /* unused = 0, > 0 specific thread # */
     int detect_zeroes; /* enum virDomainDiskDetectZeroes */
+    int metadata_cache_size; /* enum virDomainDiskMetadataCacheSize */
     char *domain_name; /* backend domain name */
     unsigned int queues;
     virDomainVirtioOptionsPtr virtio;
@@ -3408,6 +3416,7 @@ VIR_ENUM_DECL(virDomainDeviceSGIO)
 VIR_ENUM_DECL(virDomainDiskTray)
 VIR_ENUM_DECL(virDomainDiskDiscard)
 VIR_ENUM_DECL(virDomainDiskDetectZeroes)
+VIR_ENUM_DECL(virDomainDiskMetadataCacheSize)
 VIR_ENUM_DECL(virDomainDiskMirrorState)
 VIR_ENUM_DECL(virDomainController)
 VIR_ENUM_DECL(virDomainControllerModelPCI)
diff --git a/tests/qemuxml2argvdata/disk-metadata_cache_size.xml 
b/tests/qemuxml2argvdata/disk-metadata_cache_size.xml
new file mode 100644
index 0000000..121171a
--- /dev/null
+++ b/tests/qemuxml2argvdata/disk-metadata_cache_size.xml
@@ -0,0 +1,35 @@
+<domain type='qemu'>
+  <name>test</name>
+  <uuid>468404ad-d49c-40f2-9e14-02294f9c1be3</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <currentMemory unit='KiB'>1048576</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+    <boot dev='cdrom'/>
+    <boot dev='hd'/>
+    <bootmenu enable='yes'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>restart</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <disk type='file' device='disk'>
+      <driver name='qemu' type='qcow2' metadata_cache_size='maximum'/>
+      <source file='/var/lib/libvirt/images/f14.img'/>
+      <target dev='vda' bus='virtio'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' 
function='0x0'/>
+    </disk>
+    <controller type='usb' index='0'/>
+    <controller type='virtio-serial' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' 
function='0x0'/>
+    </controller>
+    <controller type='ide' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2xmloutdata/disk-metadata_cache_size.xml 
b/tests/qemuxml2xmloutdata/disk-metadata_cache_size.xml
new file mode 100644
index 0000000..2ca7dc4
--- /dev/null
+++ b/tests/qemuxml2xmloutdata/disk-metadata_cache_size.xml
@@ -0,0 +1,41 @@
+<domain type='qemu'>
+  <name>test</name>
+  <uuid>468404ad-d49c-40f2-9e14-02294f9c1be3</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <currentMemory unit='KiB'>1048576</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+    <boot dev='cdrom'/>
+    <boot dev='hd'/>
+    <bootmenu enable='yes'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>restart</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <disk type='file' device='disk'>
+      <driver name='qemu' type='qcow2' metadata_cache_size='maximum'/>
+      <source file='/var/lib/libvirt/images/f14.img'/>
+      <target dev='vda' bus='virtio'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' 
function='0x0'/>
+    </disk>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x2'/>
+    </controller>
+    <controller type='virtio-serial' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' 
function='0x0'/>
+    </controller>
+    <controller type='ide' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' 
function='0x1'/>
+    </controller>
+    <controller type='pci' index='0' model='pci-root'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='virtio'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' 
function='0x0'/>
+    </memballoon>
+  </devices>
+</domain>
diff --git a/tests/qemuxml2xmltest.c b/tests/qemuxml2xmltest.c
index 82e2c0e..4aa845c 100644
--- a/tests/qemuxml2xmltest.c
+++ b/tests/qemuxml2xmltest.c
@@ -1265,6 +1265,8 @@ mymain(void)
     DO_TEST("riscv64-virt",
             QEMU_CAPS_DEVICE_VIRTIO_MMIO);
 
+    DO_TEST("disk-metadata_cache_size", NONE);
+
     if (getenv("LIBVIRT_SKIP_CLEANUP") == NULL)
         virFileDeleteTree(fakerootdir);
 
-- 
1.8.3.1

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