conf: Add support of zero-detection for disks

This option allows or disallows detection of zero-writes if it is set to
"on" or "off", respectively.  It can be also set to "unmap" in which
case it will try discarding that part of image based on the value of the
"discard" option.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>

docs/formatdomain.html.in

@@ -2564,6 +2564,18 @@
             (ignore the discard request).
             <span class='since'>Since 1.0.6 (QEMU and KVM only)</span>
           </li>
+          <li>
+            The optional <code>detect_zeroes</code> attribute controls whether
+            to detect zero write requests.  The value can be "off", "on" or
+            "unmap".  First two values turn the detection off and on,
+            respectively.  The third value ("unmap") turns the detection on
+            and additionally tries to discard such areas from the image based
+            on the value of <code>discard</code> above (it will act as "on"
+            if <code>discard</code> is set to "ignore").  NB enabling the
+            detection is a compute intensive operation, but can save file
+            space and/or time on slow media.
+            <span class='since'>Since 1.3.6</span>
+          </li>
           <li>
             The optional <code>iothread</code> attribute assigns the
             disk to an IOThread as defined by the range for the domain

docs/schemas/domaincommon.rng

@@ -1618,6 +1618,9 @@
       <optional>
         <ref name="driverIOThread"/>
       </optional>
+      <optional>
+        <ref name="detect_zeroes"/>
+      </optional>
       <empty/>
     </element>
   </define>
@@ -1702,6 +1705,15 @@
       <ref name="unsignedInt"/>
     </attribute>
   </define>
+  <define name="detect_zeroes">
+    <attribute name='detect_zeroes'>
+      <choice>
+        <value>off</value>
+        <value>on</value>
+        <value>unmap</value>
+      </choice>
+    </attribute>
+  </define>
   <define name="controller">
     <element name="controller">
       <optional>

src/conf/domain_conf.c

@@ -807,6 +807,12 @@ VIR_ENUM_IMPL(virDomainDiskDiscard, VIR_DOMAIN_DISK_DISCARD_LAST,
               "unmap",
               "ignore")
 
+VIR_ENUM_IMPL(virDomainDiskDetectZeroes, VIR_DOMAIN_DISK_DETECT_ZEROES_LAST,
+              "default",
+              "off",
+              "on",
+              "unmap")
+
 VIR_ENUM_IMPL(virDomainDiskMirrorState, VIR_DOMAIN_DISK_MIRROR_STATE_LAST,
               "none",
               "yes",
@@ -7378,6 +7384,14 @@ virDomainDiskDefDriverParseXML(virDomainDiskDefPtr def,
         VIR_FREE(tmp);
     }
 
+    if ((tmp = virXMLPropString(cur, "detect_zeroes")) &&
+        (def->detect_zeroes = virDomainDiskDetectZeroesTypeFromString(tmp)) <= 0) {
+        virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                       _("unknown driver detect_zeroes value '%s'"), tmp);
+        goto cleanup;
+    }
+    VIR_FREE(tmp);
+
     ret = 0;
 
  cleanup:
@@ -19631,6 +19645,7 @@ virDomainDiskDefFormat(virBufferPtr buf,
     const char *copy_on_read = virTristateSwitchTypeToString(def->copy_on_read);
     const char *sgio = virDomainDeviceSGIOTypeToString(def->sgio);
     const char *discard = virDomainDiskDiscardTypeToString(def->discard);
+    const char *detect_zeroes = virDomainDiskDetectZeroesTypeToString(def->detect_zeroes);
 
     if (!type || !def->src->type) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
@@ -19685,7 +19700,7 @@ virDomainDiskDefFormat(virBufferPtr buf,
     if (def->src->driverName || def->src->format > 0 || def->cachemode ||
         def->error_policy || def->rerror_policy || def->iomode ||
         def->ioeventfd || def->event_idx || def->copy_on_read ||
-        def->discard || def->iothread) {
+        def->discard || def->iothread || def->detect_zeroes) {
         virBufferAddLit(buf, "<driver");
         virBufferEscapeString(buf, " name='%s'", def->src->driverName);
         if (def->src->format > 0)
@@ -19709,6 +19724,8 @@ virDomainDiskDefFormat(virBufferPtr buf,
             virBufferAsprintf(buf, " discard='%s'", discard);
         if (def->iothread)
             virBufferAsprintf(buf, " iothread='%u'", def->iothread);
+        if (def->detect_zeroes)
+            virBufferAsprintf(buf, " detect_zeroes='%s'", detect_zeroes);
         virBufferAddLit(buf, "/>\n");
     }
 

src/conf/domain_conf.h

@@ -528,6 +528,15 @@ typedef enum {
     VIR_DOMAIN_DISK_DISCARD_LAST
 } virDomainDiskDiscard;
 
+typedef enum {
+    VIR_DOMAIN_DISK_DETECT_ZEROES_DEFAULT = 0,
+    VIR_DOMAIN_DISK_DETECT_ZEROES_OFF,
+    VIR_DOMAIN_DISK_DETECT_ZEROES_ON,
+    VIR_DOMAIN_DISK_DETECT_ZEROES_UNMAP,
+
+    VIR_DOMAIN_DISK_DETECT_ZEROES_LAST
+} virDomainDiskDetectZeroes;
+
 typedef struct _virDomainBlockIoTuneInfo virDomainBlockIoTuneInfo;
 struct _virDomainBlockIoTuneInfo {
     unsigned long long total_bytes_sec;
@@ -606,6 +615,7 @@ struct _virDomainDiskDef {
     int sgio; /* enum virDomainDeviceSGIO */
     int discard; /* enum virDomainDiskDiscard */
     unsigned int iothread; /* unused = 0, > 0 specific thread # */
+    int detect_zeroes; /* enum virDomainDiskDetectZeroes */
     char *domain_name; /* backend domain name */
 };
 
@@ -2937,6 +2947,7 @@ VIR_ENUM_DECL(virDomainDiskIo)
 VIR_ENUM_DECL(virDomainDeviceSGIO)
 VIR_ENUM_DECL(virDomainDiskTray)
 VIR_ENUM_DECL(virDomainDiskDiscard)
+VIR_ENUM_DECL(virDomainDiskDetectZeroes)
 VIR_ENUM_DECL(virDomainDiskMirrorState)
 VIR_ENUM_DECL(virDomainController)
 VIR_ENUM_DECL(virDomainControllerModelPCI)

src/libvirt_private.syms

@@ -267,6 +267,8 @@ virDomainDiskDefForeachPath;
 virDomainDiskDefFree;
 virDomainDiskDefNew;
 virDomainDiskDefSourceParse;
+virDomainDiskDetectZeroesTypeFromString;
+virDomainDiskDetectZeroesTypeToString;
 virDomainDiskDeviceTypeToString;
 virDomainDiskDiscardTypeToString;
 virDomainDiskErrorPolicyTypeFromString;

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-detect-zeroes.xml

@@ -0,0 +1,45 @@
+<domain type='qemu'>
+  <name>test</name>
+  <uuid>92d7a226-cfae-425b-a6d3-00bbf9ec5c9e</uuid>
+  <memory unit='KiB'>1048576</memory>
+  <currentMemory unit='KiB'>1048576</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc-0.13'>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</emulator>
+    <disk type='file' device='disk'>
+      <driver name='qemu' type='qcow2' discard='unmap' detect_zeroes='unmap'/>
+      <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>
+    <disk type='file' device='cdrom'>
+      <driver discard='ignore' detect_zeroes='off'/>
+      <source file='/var/lib/libvirt/Fedora-14-x86_64-Live-KDE.iso'/>
+      <target dev='hdc' bus='ide'/>
+      <readonly/>
+      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
+    </disk>
+    <controller type='usb' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
+    </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>

tests/qemuxml2xmloutdata/qemuxml2xmlout-disk-drive-detect-zeroes.xml

@@ -0,0 +1 @@
+../qemuxml2argvdata/qemuxml2argv-disk-drive-detect-zeroes.xml

tests/qemuxml2xmltest.c

@@ -566,6 +566,7 @@ mymain(void)
     DO_TEST("disk-source-pool-mode");
 
     DO_TEST("disk-drive-discard");
+    DO_TEST("disk-drive-detect-zeroes");
 
     DO_TEST("virtio-rng-random");
     DO_TEST("virtio-rng-egd");