block_resize: Implement qemu driver method

It requires the domain is running, otherwise fails. Resize to a lower
size is supported, but should be used with extreme caution.

In order to prohibit the "size" overflowing after multiplied by
1024. We do checking in the codes. For QMP mode, the default units
is Bytes, the passed size needs to be multiplied by 1024, however,
for HMP mode, the default units is "Megabytes", the passed "size"
needs to be divided by 1024 then.

src/qemu/qemu_driver.c

@@ -7056,6 +7056,96 @@ qemuGetSchedulerParameters(virDomainPtr dom,
                                            VIR_DOMAIN_AFFECT_CURRENT);
 }
 
+/**
+ * Resize a block device while a guest is running. Resize to a lower size
+ * is supported, but should be used with extreme caution.  Note that it
+ * only supports to resize image files, it can't resize block devices
+ * like LVM volumes.
+ */
+static int
+qemuDomainBlockResize (virDomainPtr dom,
+                       const char *path,
+                       unsigned long long size,
+                       unsigned int flags)
+{
+    struct qemud_driver *driver = dom->conn->privateData;
+    virDomainObjPtr vm;
+    qemuDomainObjPrivatePtr priv;
+    int ret = -1, i;
+    char *device = NULL;
+    virDomainDiskDefPtr disk = NULL;
+
+    virCheckFlags(0, -1);
+
+    if (path[0] == '\0') {
+        qemuReportError(VIR_ERR_INVALID_ARG,
+                        "%s", _("empty path"));
+        return -1;
+    }
+
+    if (size > ULLONG_MAX / 1024) {
+        qemuReportError(VIR_ERR_INVALID_ARG,
+                        _("size must be less than %llu"),
+                        ULLONG_MAX / 1024);
+        return -1;
+    }
+
+    qemuDriverLock(driver);
+    vm = virDomainFindByUUID(&driver->domains, dom->uuid);
+    qemuDriverUnlock(driver);
+
+    if (!vm) {
+        char uuidstr[VIR_UUID_STRING_BUFLEN];
+        virUUIDFormat(dom->uuid, uuidstr);
+        qemuReportError(VIR_ERR_NO_DOMAIN,
+                        _("no domain matching uuid '%s'"), uuidstr);
+        goto cleanup;
+    }
+
+    priv = vm->privateData;
+
+    if (qemuDomainObjBeginJob(driver, vm, QEMU_JOB_MODIFY) < 0)
+        goto cleanup;
+
+    if (!virDomainObjIsActive(vm)) {
+        qemuReportError(VIR_ERR_OPERATION_INVALID,
+                        "%s", _("domain is not running"));
+        goto endjob;
+    }
+
+    if ((i = virDomainDiskIndexByName(vm->def, path, false)) < 0) {
+        qemuReportError(VIR_ERR_INVALID_ARG,
+                        _("invalid path: %s"), path);
+        goto cleanup;
+    }
+    disk = vm->def->disks[i];
+
+    if (virAsprintf(&device, "%s%s", QEMU_DRIVE_HOST_PREFIX,
+                    disk->info.alias) < 0) {
+        virReportOOMError();
+        goto endjob;
+    }
+
+    qemuDomainObjEnterMonitor(driver, vm);
+    if (qemuMonitorBlockResize(priv->mon, device, size) < 0) {
+        qemuDomainObjExitMonitor(driver, vm);
+        goto endjob;
+    }
+    qemuDomainObjExitMonitor(driver, vm);
+
+    ret = 0;
+
+endjob:
+    if (qemuDomainObjEndJob(driver, vm) == 0)
+        vm = NULL;
+
+cleanup:
+    VIR_FREE(device);
+    if (vm)
+        virDomainObjUnlock(vm);
+    return ret;
+}
+
 /* This uses the 'info blockstats' monitor command which was
  * integrated into both qemu & kvm in late 2007.  If the command is
  * not supported we detect this and return the appropriate error.
@@ -10849,6 +10939,7 @@ static virDriver qemuDriver = {
     .domainSetSchedulerParameters = qemuSetSchedulerParameters, /* 0.7.0 */
     .domainSetSchedulerParametersFlags = qemuSetSchedulerParametersFlags, /* 0.9.2 */
     .domainMigratePerform = qemudDomainMigratePerform, /* 0.5.0 */
+    .domainBlockResize = qemuDomainBlockResize, /* 0.9.8 */
     .domainBlockStats = qemuDomainBlockStats, /* 0.4.1 */
     .domainBlockStatsFlags = qemuDomainBlockStatsFlags, /* 0.9.5 */
     .domainInterfaceStats = qemudDomainInterfaceStats, /* 0.4.1 */