qemu: Support copy on read for disk

The new introduced optional attribute "copy_on_read</code> controls whether to copy read backing file into the image file. The value can be either "on" or "off". Copy-on-read avoids accessing the same backing file sectors repeatedly and is useful when the backing file is over a slow network. By default copy-on-read is off.
2025-02-20 18:32:20 +00:00 · 2012-01-12 17:31:14 +08:00 · 2012-01-12 17:31:14 +08:00 · 5edfcaae6f
commit 5edfcaae6f
parent b54de0830a
12 changed files with 137 additions and 2 deletions
--- a/docs/formatdomain.html.in
+++ b/docs/formatdomain.html.in
@ -1202,6 +1202,15 @@
            <b>In general you should leave this option alone, unless you
            are very certain you know what you are doing.</b>
          </li>
+          <li>
+            The optional <code>copy_on_read</code> attribute controls
+            wether to copy read backing file into the image file. The
+            value can be either "on" or "off".
+            Copy-on-read avoids accessing the same backing file sectors
+            repeatedly and is useful when the backing file is over a slow
+            network. By default copy-on-read is off.
+            <span class='since'>Since 0.9.10 (QEMU and KVM only)</span>
+          </li>
        </ul>
      </dd>
      <dt><code>boot</code></dt>
--- a/docs/schemas/domaincommon.rng
+++ b/docs/schemas/domaincommon.rng
@ -958,6 +958,9 @@
      <optional>
        <ref name="event_idx"/>
      </optional>
+      <optional>
+        <ref name="copy_on_read"/>
+      </optional>
      <empty/>
    </element>
  </define>
@ -1025,6 +1028,14 @@
      </choice>
    </attribute>
  </define>
+  <define name="copy_on_read">
+    <attribute name='copy_on_read'>
+      <choice>
+        <value>on</value>
+        <value>off</value>
+      </choice>
+    </attribute>
+  </define>
  <define name="controller">
    <element name="controller">
      <choice>
--- a/src/conf/domain_conf.c
+++ b/src/conf/domain_conf.c
@ -209,6 +209,11 @@ VIR_ENUM_IMPL(virDomainVirtioEventIdx, VIR_DOMAIN_VIRTIO_EVENT_IDX_LAST,
              "on",
              "off")

+VIR_ENUM_IMPL(virDomainDiskCopyOnRead, VIR_DOMAIN_DISK_COPY_ON_READ_LAST,
+              "default",
+              "on",
+              "off")
+
 VIR_ENUM_IMPL(virDomainDiskSnapshot, VIR_DOMAIN_DISK_SNAPSHOT_LAST,
              "default",
              "no",
@ -2783,6 +2788,7 @@ virDomainDiskDefParseXML(virCapsPtr caps,
    char *iotag = NULL;
    char *ioeventfd = NULL;
    char *event_idx = NULL;
+    char *copy_on_read = NULL;
    char *devaddr = NULL;
    virStorageEncryptionPtr encryption = NULL;
    char *serial = NULL;
@ -2911,6 +2917,7 @@ virDomainDiskDefParseXML(virCapsPtr caps,
                iotag = virXMLPropString(cur, "io");
                ioeventfd = virXMLPropString(cur, "ioeventfd");
                event_idx = virXMLPropString(cur, "event_idx");
+                copy_on_read = virXMLPropString(cur, "copy_on_read");
            } else if (xmlStrEqual(cur->name, BAD_CAST "auth")) {
                authUsername = virXMLPropString(cur, "username");
                if (authUsername == NULL) {
@ -3226,6 +3233,17 @@ virDomainDiskDefParseXML(virCapsPtr caps,
        def->event_idx = idx;
    }

+    if (copy_on_read) {
+        int cor;
+        if ((cor = virDomainDiskCopyOnReadTypeFromString(copy_on_read)) <= 0) {
+            virDomainReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                                 _("unknown disk copy_on_read mode '%s'"),
+                                 copy_on_read);
+            goto error;
+        }
+        def->copy_on_read = cor;
+    }
+
    if (devaddr) {
        if (virDomainParseLegacyDeviceAddress(devaddr,
                                              &def->info.addr.pci) < 0) {
@ -3319,6 +3337,7 @@ cleanup:
    VIR_FREE(iotag);
    VIR_FREE(ioeventfd);
    VIR_FREE(event_idx);
+    VIR_FREE(copy_on_read);
    VIR_FREE(devaddr);
    VIR_FREE(serial);
    virStorageEncryptionFree(encryption);
@ -9878,6 +9897,7 @@ virDomainDiskDefFormat(virBufferPtr buf,
    const char *iomode = virDomainDiskIoTypeToString(def->iomode);
    const char *ioeventfd = virDomainIoEventFdTypeToString(def->ioeventfd);
    const char *event_idx = virDomainVirtioEventIdxTypeToString(def->event_idx);
+    const char *copy_on_read = virDomainVirtioEventIdxTypeToString(def->copy_on_read);
    const char *startupPolicy = virDomainStartupPolicyTypeToString(def->startupPolicy);

    char uuidstr[VIR_UUID_STRING_BUFLEN];
@ -9918,7 +9938,7 @@ virDomainDiskDefFormat(virBufferPtr buf,
    virBufferAddLit(buf, ">\n");

    if (def->driverName || def->driverType || def->cachemode ||
-        def->ioeventfd || def->event_idx) {
+        def->ioeventfd || def->event_idx || def->copy_on_read) {
        virBufferAddLit(buf, "      <driver");
        if (def->driverName)
            virBufferAsprintf(buf, " name='%s'", def->driverName);
@ -9936,6 +9956,8 @@ virDomainDiskDefFormat(virBufferPtr buf,
            virBufferAsprintf(buf, " ioeventfd='%s'", ioeventfd);
        if (def->event_idx)
            virBufferAsprintf(buf, " event_idx='%s'", event_idx);
+        if (def->copy_on_read)
+            virBufferAsprintf(buf, " copy_on_read='%s'", copy_on_read);
        virBufferAddLit(buf, "/>\n");
    }

--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@ -308,6 +308,14 @@ enum virDomainVirtioEventIdx {
    VIR_DOMAIN_VIRTIO_EVENT_IDX_LAST
 };

+enum virDomainDiskCopyOnRead {
+    VIR_DOMAIN_DISK_COPY_ON_READ_DEFAULT = 0,
+    VIR_DOMAIN_DISK_COPY_ON_READ_ON,
+    VIR_DOMAIN_DISK_COPY_ON_READ_OFF,
+
+    VIR_DOMAIN_DISK_COPY_ON_READ_LAST
+};
+
 enum virDomainDiskSnapshot {
    VIR_DOMAIN_DISK_SNAPSHOT_DEFAULT = 0,
    VIR_DOMAIN_DISK_SNAPSHOT_NO,
@ -384,6 +392,7 @@ struct _virDomainDiskDef {
    int iomode;
    int ioeventfd;
    int event_idx;
+    int copy_on_read;
    int snapshot; /* enum virDomainDiskSnapshot */
    int startupPolicy; /* enum virDomainStartupPolicy */
    unsigned int readonly : 1;
@ -1969,6 +1978,7 @@ VIR_ENUM_DECL(virDomainDiskSecretType)
 VIR_ENUM_DECL(virDomainDiskSnapshot)
 VIR_ENUM_DECL(virDomainIoEventFd)
 VIR_ENUM_DECL(virDomainVirtioEventIdx)
+VIR_ENUM_DECL(virDomainDiskCopyOnRead)
 VIR_ENUM_DECL(virDomainController)
 VIR_ENUM_DECL(virDomainControllerModelSCSI)
 VIR_ENUM_DECL(virDomainControllerModelUSB)
--- a/src/libvirt_private.syms
+++ b/src/libvirt_private.syms
@ -290,6 +290,8 @@ virDomainDeviceTypeToString;
 virDomainDiskBusTypeToString;
 virDomainDiskCacheTypeFromString;
 virDomainDiskCacheTypeToString;
+virDomainDiskCopyOnReadTypeFromString;
+virDomainDiskCopyOnReadTypeToString;
 virDomainDiskDefAssignAddress;
 virDomainDiskDefForeachPath;
 virDomainDiskDefFree;
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@ -147,6 +147,7 @@ VIR_ENUM_IMPL(qemuCaps, QEMU_CAPS_LAST,

              "virtio-blk-pci.scsi",
              "blk-sg-io",
+              "drive-copy-on-read",
    );

 struct qemu_feature_flags {
@ -1026,6 +1027,8 @@ qemuCapsComputeCmdFlags(const char *help,
            qemuCapsSet(flags, QEMU_CAPS_DRIVE_READONLY);
        if (strstr(help, "aio=threads|native"))
            qemuCapsSet(flags, QEMU_CAPS_DRIVE_AIO);
+        if (strstr(help, "copy-on-read=on|off"))
+            qemuCapsSet(flags, QEMU_CAPS_DRIVE_COPY_ON_READ);
    }
    if ((p = strstr(help, "-vga")) && !strstr(help, "-std-vga")) {
        const char *nl = strstr(p, "\n");
--- a/src/qemu/qemu_capabilities.h
+++ b/src/qemu/qemu_capabilities.h
@ -120,6 +120,7 @@ enum qemuCapsFlags {

    QEMU_CAPS_VIRTIO_BLK_SCSI    = 80, /* virtio-blk-pci.scsi */
    QEMU_CAPS_VIRTIO_BLK_SG_IO   = 81, /* support for SG_IO commands, reportedly added in 0.11 */
+    QEMU_CAPS_DRIVE_COPY_ON_READ = 82, /* -drive copy-on-read */

    QEMU_CAPS_LAST,                   /* this must always be the last item */
 };
--- a/src/qemu/qemu_command.c
+++ b/src/qemu/qemu_command.c
@ -1929,6 +1929,17 @@ qemuBuildDriveStr(virConnectPtr conn ATTRIBUTE_UNUSED,
        virBufferAddLit(&opt, ",cache=off");
    }

+    if (disk->copy_on_read) {
+        if (qemuCapsGet(qemuCaps, QEMU_CAPS_DRIVE_COPY_ON_READ)) {
+            virBufferAsprintf(&opt, ",copy-on-read=%s",
+                              virDomainDiskCopyOnReadTypeToString(disk->copy_on_read));
+        } else {
+            qemuReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                            _("copy_on_read is not supported by this QEMU binary"));
+            goto error;
+        }
+    }
+
    if (qemuCapsGet(qemuCaps, QEMU_CAPS_MONITOR_JSON)) {
        const char *wpolicy = NULL, *rpolicy = NULL;

--- a/tests/qemuhelptest.c
+++ b/tests/qemuhelptest.c
@ -592,7 +592,8 @@ mymain(void)
            QEMU_CAPS_PCI_ROMBAR,
            QEMU_CAPS_NO_ACPI,
            QEMU_CAPS_VIRTIO_BLK_SCSI,
-            QEMU_CAPS_VIRTIO_BLK_SG_IO);
+            QEMU_CAPS_VIRTIO_BLK_SG_IO,
+            QEMU_CAPS_DRIVE_COPY_ON_READ);
    DO_TEST("qemu-1.0", 1000000, 0, 0,
            QEMU_CAPS_VNC_COLON,
            QEMU_CAPS_NO_REBOOT,
--- a/tests/qemuxml2argvdata/qemuxml2argv-disk-copy_on_read.args
+++ b/tests/qemuxml2argvdata/qemuxml2argv-disk-copy_on_read.args
@ -0,0 +1,11 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
+/usr/bin/qemu -S -M pc-0.13 -m 1024 -smp 1 -nodefaults \
+-monitor unix:/tmp/test-monitor,server,nowait -no-acpi \
+-boot dc -device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x6 \
+-drive file=/var/lib/libvirt/images/f14.img,if=none,id=drive-virtio-disk0,copy-on-read=on \
+-device virtio-blk-pci,scsi=off,bus=pci.0,addr=0x4,drive=drive-virtio-disk0,id=virtio-disk0 \
+-drive file=/var/lib/libvirt/Fedora-14-x86_64-Live-KDE.iso,if=none,media=cdrom,id=drive-ide0-1-0 \
+-device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 \
+-device virtio-net-pci,tx=bh,vlan=0,id=net0,mac=52:54:00:e5:48:58,bus=pci.0,addr=0x3 \
+-net user,vlan=0,name=hostnet0 -serial pty -usb -vnc 127.0.0.1:-809 -std-vga \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x5
--- a/tests/qemuxml2argvdata/qemuxml2argv-disk-copy_on_read.xml
+++ b/tests/qemuxml2argvdata/qemuxml2argv-disk-copy_on_read.xml
@ -0,0 +1,50 @@
+<domain type='qemu'>
+  <name>test</name>
+  <memory>1048576</memory>
+  <vcpu>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' copy_on_read='on'/>
+      <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 name='qemu' type='raw'/>
+      <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' unit='0'/>
+    </disk>
+    <interface type='user'>
+      <mac address='52:54:00:e5:48:58'/>
+      <model type='virtio'/>
+      <driver name='vhost' txmode='iothread'/>
+    </interface>
+    <controller type='virtio-serial' index='0'>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
+    </controller>
+    <serial type='pty'>
+      <target port='0'/>
+    </serial>
+    <console type='pty'>
+      <target type='serial' port='0'/>
+    </console>
+    <graphics type='vnc' port='5091' autoport='no' listen='127.0.0.1'/>
+    <video>
+      <model type='vga' vram='9216' heads='1'/>
+      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
+    </video>
+  </devices>
+</domain>
--- a/tests/qemuxml2argvtest.c
+++ b/tests/qemuxml2argvtest.c
@ -439,6 +439,10 @@ mymain(void)
            QEMU_CAPS_DRIVE, QEMU_CAPS_VIRTIO_IOEVENTFD,
            QEMU_CAPS_VIRTIO_TX_ALG, QEMU_CAPS_DEVICE,
            QEMU_CAPS_VIRTIO_BLK_SCSI, QEMU_CAPS_VIRTIO_BLK_SG_IO);
+    DO_TEST("disk-copy_on_read", false,
+            QEMU_CAPS_DRIVE, QEMU_CAPS_DRIVE_COPY_ON_READ,
+            QEMU_CAPS_VIRTIO_TX_ALG, QEMU_CAPS_DEVICE,
+            QEMU_CAPS_VIRTIO_BLK_SCSI, QEMU_CAPS_VIRTIO_BLK_SG_IO);
    DO_TEST("disk-snapshot", false,
            QEMU_CAPS_DRIVE, QEMU_CAPS_DRIVE_CACHE_V2, QEMU_CAPS_DRIVE_FORMAT);
    DO_TEST("event_idx", false,