qemu: Support discard for disk

QEMU introduced "discard" option for drive since commit a9384aff53,

<...>
@var{discard} is one of "ignore" (or "off") or "unmap" (or "on") and
controls whether @dfn{discard} (also known as @dfn{trim} or @dfn{unmap})
requests are ignored or passed to the filesystem.  Some machine types
may not support discard requests.
</...>

This patch exposes the support in libvirt.

QEMU supported "discard" for "-drive" since v1.5.0-rc0:

% git tag --contains a9384aff53
contains
v1.5.0-rc0
v1.5.0-rc1

So this only detects the capability bit using virQEMUCapsProbeQMPCommandLine.

docs/formatdomain.html.in

@@ -1702,6 +1702,14 @@
             network. By default copy-on-read is off.
             <span class='since'>Since 0.9.10 (QEMU and KVM only)</span>
           </li>
+          <li>
+            The optional <code>discard</code> attribute controls whether
+            to discard (also known as "trim" or "unmap") requests are
+            ignored or passed to the filesystem. The value can be either
+            "on" (allow the discard request to be passed) or "off" (ingore
+            the discard request).
+            <span class='since'>Since 1.0.6 (QEMU and KVM only)</span>
+          </li>
         </ul>
       </dd>
       <dt><code>boot</code></dt>

docs/schemas/domaincommon.rng

@@ -1311,6 +1311,9 @@
       <optional>
         <ref name="copy_on_read"/>
       </optional>
+      <optional>
+        <ref name="discard"/>
+      </optional>
       <empty/>
     </element>
   </define>
@@ -1407,6 +1410,14 @@
       </choice>
     </attribute>
     </define>
+  <define name="discard">
+    <attribute name='discard'>
+      <choice>
+        <value>on</value>
+        <value>off</value>
+      </choice>
+    </attribute>
+  </define>
   <define name="controller">
     <element name="controller">
       <attribute name="index">

src/conf/domain_conf.c

@@ -743,6 +743,10 @@ VIR_ENUM_IMPL(virDomainTPMModel, VIR_DOMAIN_TPM_MODEL_LAST,
 VIR_ENUM_IMPL(virDomainTPMBackend, VIR_DOMAIN_TPM_TYPE_LAST,
               "passthrough")
 
+VIR_ENUM_IMPL(virDomainDiskDiscard, VIR_DOMAIN_DISK_DISCARD_LAST,
+              "default",
+              "on",
+              "off")
 
 #define VIR_DOMAIN_XML_WRITE_FLAGS  VIR_DOMAIN_XML_SECURE
 #define VIR_DOMAIN_XML_READ_FLAGS   VIR_DOMAIN_XML_INACTIVE
@@ -4534,6 +4538,7 @@ virDomainDiskDefParseXML(virDomainXMLOptionPtr xmlopt,
     char *wwn = NULL;
     char *vendor = NULL;
     char *product = NULL;
+    char *discard = NULL;
     int expected_secret_usage = -1;
     int auth_secret_usage = -1;
 
@@ -4761,6 +4766,7 @@ virDomainDiskDefParseXML(virDomainXMLOptionPtr xmlopt,
                 ioeventfd = virXMLPropString(cur, "ioeventfd");
                 event_idx = virXMLPropString(cur, "event_idx");
                 copy_on_read = virXMLPropString(cur, "copy_on_read");
+                discard = virXMLPropString(cur, "discard");
             } else if (!mirror && xmlStrEqual(cur->name, BAD_CAST "mirror") &&
                        !(flags & VIR_DOMAIN_XML_INACTIVE)) {
                 char *ready;
@@ -5207,6 +5213,14 @@ virDomainDiskDefParseXML(virDomainXMLOptionPtr xmlopt,
         def->copy_on_read = cor;
     }
 
+    if (discard) {
+        if ((def->discard = virDomainDiskDiscardTypeFromString(discard)) <= 0) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("unknown disk discard mode '%s'"), discard);
+            goto error;
+        }
+    }
+
     if (devaddr) {
         if (virDomainParseLegacyDeviceAddress(devaddr,
                                               &def->info.addr.pci) < 0) {
@@ -5326,6 +5340,7 @@ cleanup:
     VIR_FREE(ioeventfd);
     VIR_FREE(event_idx);
     VIR_FREE(copy_on_read);
+    VIR_FREE(discard);
     VIR_FREE(devaddr);
     VIR_FREE(serial);
     virStorageEncryptionFree(encryption);
@@ -13658,6 +13673,7 @@ virDomainDiskDefFormat(virBufferPtr buf,
     const char *event_idx = virDomainVirtioEventIdxTypeToString(def->event_idx);
     const char *copy_on_read = virDomainVirtioEventIdxTypeToString(def->copy_on_read);
     const char *sgio = virDomainDiskSGIOTypeToString(def->sgio);
+    const char *discard = virDomainDiskDiscardTypeToString(def->discard);
 
     char uuidstr[VIR_UUID_STRING_BUFLEN];
 
@@ -13734,6 +13750,8 @@ virDomainDiskDefFormat(virBufferPtr buf,
             virBufferAsprintf(buf, " event_idx='%s'", event_idx);
         if (def->copy_on_read)
             virBufferAsprintf(buf, " copy_on_read='%s'", copy_on_read);
+        if (def->discard)
+            virBufferAsprintf(buf, " discard='%s'", discard);
         virBufferAddLit(buf, "/>\n");
     }
 

src/conf/domain_conf.h

@@ -625,6 +625,14 @@ enum virDomainDiskSGIO {
     VIR_DOMAIN_DISK_SGIO_LAST
 };
 
+enum virDomainDiskDiscard {
+    VIR_DOMAIN_DISK_DISCARD_DEFAULT = 0,
+    VIR_DOMAIN_DISK_DISCARD_ON,
+    VIR_DOMAIN_DISK_DISCARD_OFF,
+
+    VIR_DOMAIN_DISK_DISCARD_LAST
+};
+
 typedef struct _virDomainBlockIoTuneInfo virDomainBlockIoTuneInfo;
 struct _virDomainBlockIoTuneInfo {
     unsigned long long total_bytes_sec;
@@ -707,6 +715,7 @@ struct _virDomainDiskDef {
     bool rawio_specified;
     int rawio; /* no = 0, yes = 1 */
     int sgio; /* enum virDomainDiskSGIO */
+    int discard; /* enum virDomainDiskDiscard */
 
     size_t nseclabels;
     virSecurityDeviceLabelDefPtr *seclabels;
@@ -2464,6 +2473,7 @@ VIR_ENUM_DECL(virDomainDiskIo)
 VIR_ENUM_DECL(virDomainDiskSecretType)
 VIR_ENUM_DECL(virDomainDiskSGIO)
 VIR_ENUM_DECL(virDomainDiskTray)
+VIR_ENUM_DECL(virDomainDiskDiscard)
 VIR_ENUM_DECL(virDomainIoEventFd)
 VIR_ENUM_DECL(virDomainVirtioEventIdx)
 VIR_ENUM_DECL(virDomainDiskCopyOnRead)

src/libvirt_private.syms

@@ -142,6 +142,7 @@ virDomainDiskDefFree;
 virDomainDiskDefGenSecurityLabelDef;
 virDomainDiskDefGetSecurityLabelDef;
 virDomainDiskDeviceTypeToString;
+virDomainDiskDiscardTypeToString;
 virDomainDiskErrorPolicyTypeFromString;
 virDomainDiskErrorPolicyTypeToString;
 virDomainDiskFindByBusAndDst;

src/qemu/qemu_capabilities.c

@@ -229,6 +229,7 @@ VIR_ENUM_IMPL(virQEMUCaps, QEMU_CAPS_LAST,
               "scsi-generic.bootindex", /* 145 */
               "mem-merge",
               "vnc-websocket",
+              "drive-discard",
     );
 
 struct _virQEMUCaps {
@@ -2244,6 +2245,7 @@ struct virQEMUCapsCommandLineProps {
 
 static struct virQEMUCapsCommandLineProps virQEMUCapsCommandLine[] = {
     { "machine", "mem-merge", QEMU_CAPS_MEM_MERGE },
+    { "drive", "discard", QEMU_CAPS_DRIVE_DISCARD },
 };
 
 static int

src/qemu/qemu_capabilities.h

@@ -186,6 +186,7 @@ enum virQEMUCapsFlags {
     QEMU_CAPS_DEVICE_SCSI_GENERIC_BOOTINDEX = 145,  /* -device scsi-generic.bootindex */
     QEMU_CAPS_MEM_MERGE          = 146, /* -machine mem-merge */
     QEMU_CAPS_VNC_WEBSOCKET      = 147, /* -vnc x:y,websocket */
+    QEMU_CAPS_DRIVE_DISCARD      = 148, /* -drive discard=off(ignore)|on(unmap) */
 
     QEMU_CAPS_LAST,                   /* this must always be the last item */
 };

src/qemu/qemu_command.c

@@ -3274,6 +3274,17 @@ qemuBuildDriveStr(virConnectPtr conn ATTRIBUTE_UNUSED,
         }
     }
 
+    if (disk->discard) {
+        if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_DRIVE_DISCARD)) {
+            virBufferAsprintf(&opt, ",discard=%s",
+                              virDomainDiskDiscardTypeToString(disk->discard));
+        } else {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s",
+                           _("discard is not supported by this QEMU binary"));
+            goto error;
+        }
+    }
+
     if (virQEMUCapsGet(qemuCaps, QEMU_CAPS_MONITOR_JSON)) {
         const char *wpolicy = NULL, *rpolicy = NULL;
 

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-discard.args

@@ -0,0 +1,8 @@
+LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test \
+/usr/bin/qemu -S -M pc-0.13 -m 1024 -smp 1 -nographic -nodefaults \
+-monitor unix:/tmp/test-monitor,server,nowait -no-acpi -boot dc -usb \
+-drive file=/var/lib/libvirt/images/f14.img,if=none,id=drive-virtio-disk0,discard=on \
+-device virtio-blk-pci,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,discard=off \
+-device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 \
+-device virtio-balloon-pci,id=balloon0,bus=pci.0,addr=0x3

tests/qemuxml2argvdata/qemuxml2argv-disk-drive-discard.xml

@@ -0,0 +1,37 @@
+<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='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' discard='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'/>
+    <controller type='ide' index='0'/>
+    <controller type='pci' index='0' model='pci-root'/>
+    <memballoon model='virtio'/>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -585,6 +585,9 @@ mymain(void)
             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-drive-discard",
+            QEMU_CAPS_DRIVE, QEMU_CAPS_DRIVE_DISCARD,
+            QEMU_CAPS_DEVICE);
     DO_TEST("disk-snapshot",
             QEMU_CAPS_DRIVE, QEMU_CAPS_DRIVE_CACHE_V2, QEMU_CAPS_DRIVE_FORMAT);
     DO_TEST("event_idx",

tests/qemuxml2xmltest.c

@@ -261,6 +261,8 @@ mymain(void)
     DO_TEST("disk-scsi-disk-vpd");
     DO_TEST("disk-source-pool");
 
+    DO_TEST("disk-drive-discard");
+
     DO_TEST("virtio-rng-random");
     DO_TEST("virtio-rng-egd");