虚拟机libvirt os machine取值

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nova代码里获取libvirt里 os type 的machine的，如果这里获取和qemu不一致，会报如下错误：

libvirtError: internal error: process exited while connecting to monitor: 2017-10-10T06:45:38.821223Z qemu-kvm: -machine pc-i440fx-rhel7.3.0,accel=kvm,usb=off,dump-guest-core=off: unsupported machine type2017-10-10 14:45:39.131 150753 ERROR oslo_messaging.rpc.server Use -machine help to list supported machines

一般可以用virsh dumpxml instance-name 可以看到 os type 段

  <os>    <type arch='x86_64' machine='pc-i440fx-2.6'>hvm</type>    <boot dev='hd'/>    <smbios mode='sysinfo'/>  </os>

获取qemu-kvm支持的machine列表

[root@nova02 ~]# /usr/libexec/qemu-kvm -machine helpSupported machines are:pc                   Standard PC (i440FX + PIIX, 1996) (alias of pc-i440fx-2.6)pc-i440fx-2.6        Standard PC (i440FX + PIIX, 1996) (default)pc-i440fx-2.5        Standard PC (i440FX + PIIX, 1996)pc-i440fx-2.4        Standard PC (i440FX + PIIX, 1996)pc-i440fx-2.3        Standard PC (i440FX + PIIX, 1996)pc-i440fx-2.2        Standard PC (i440FX + PIIX, 1996)pc-i440fx-2.1        Standard PC (i440FX + PIIX, 1996)pc-i440fx-2.0        Standard PC (i440FX + PIIX, 1996)pc-i440fx-1.7        Standard PC (i440FX + PIIX, 1996)pc-i440fx-1.6        Standard PC (i440FX + PIIX, 1996)pc-i440fx-1.5        Standard PC (i440FX + PIIX, 1996)pc-i440fx-1.4        Standard PC (i440FX + PIIX, 1996)pc-1.3               Standard PC (i440FX + PIIX, 1996)pc-1.2               Standard PC (i440FX + PIIX, 1996)pc-1.1               Standard PC (i440FX + PIIX, 1996)pc-1.0               Standard PC (i440FX + PIIX, 1996)pc-0.15              Standard PC (i440FX + PIIX, 1996)pc-0.14              Standard PC (i440FX + PIIX, 1996)pc-0.13              Standard PC (i440FX + PIIX, 1996)pc-0.12              Standard PC (i440FX + PIIX, 1996)pc-0.11              Standard PC (i440FX + PIIX, 1996)pc-0.10              Standard PC (i440FX + PIIX, 1996)q35                  Standard PC (Q35 + ICH9, 2009) (alias of pc-q35-2.6)pc-q35-2.6           Standard PC (Q35 + ICH9, 2009)pc-q35-2.5           Standard PC (Q35 + ICH9, 2009)pc-q35-2.4           Standard PC (Q35 + ICH9, 2009)isapc                ISA-only PCnone                 empty machine

下面看下nova里如何设置这个machine的

    def _machine_type_mappings(self):        mappings = {}        for mapping in CONF.libvirt.hw_machine_type:            host_arch, _, machine_type = mapping.partition('=')            mappings[host_arch] = machine_type        return mappings    def _get_machine_type(self, image_meta, caps):        # The underlying machine type can be set as an image attribute,        # or otherwise based on some architecture specific defaults        mach_type = None        if image_meta.properties.get('hw_machine_type') is not None:            mach_type = image_meta.properties.hw_machine_type        else:            # For ARM systems we will default to vexpress-a15 for armv7            # and virt for aarch64            if caps.host.cpu.arch == fields.Architecture.ARMV7:                mach_type = "vexpress-a15"            if caps.host.cpu.arch == fields.Architecture.AARCH64:                mach_type = "virt"            if caps.host.cpu.arch in (fields.Architecture.S390,                                      fields.Architecture.S390X):                mach_type = 's390-ccw-virtio'            # If set in the config, use that as the default.            if CONF.libvirt.hw_machine_type:                mappings = self._machine_type_mappings()                mach_type = mappings.get(caps.host.cpu.arch)        return mach_type

glance 设置 hw_machine_type

glance image-update --property hw_machine_type=pc-i440fx-2.6 06865811-b430-414a-8ff2-4eeb2b608c77

从以上代码可以得出，如果image镜像信息里有 hw_machine_type 就直接用了，如果没有就判断caps.host.cpu.arch，如果 arch是x86，就会去 CONF.libvirt.hw_machine_type里找，如果都没有，就会返回空

如果arch 是 x86后，生xml后，libvirt会根据情况生成

下面我们来看libvirt是如何生成这个machine的

    if (!(qemuCaps = virQEMUCapsCacheLookup(driver->qemuCapsCache,                                            def->emulator)))           获取qemu cap        goto cleanup;    if (qemuCanonicalizeMachine(def, qemuCaps) < 0)        goto cleanup;

static intqemuCanonicalizeMachine(virDomainDefPtr def, virQEMUCapsPtr qemuCaps){    const char *canon;    if (!(canon = virQEMUCapsGetCanonicalMachine(qemuCaps, def->os.machine)))               return 0;    if (STRNEQ(canon, def->os.machine)) {        char *tmp;        if (VIR_STRDUP(tmp, canon) < 0)            return -1;        VIR_FREE(def->os.machine);        def->os.machine = tmp;      把从qemu获取到的machine赋值给os.mahcine    }    return 0;}

virQEMUCapsNewForBinaryInternal

libvirt这段代码，还不太明白，有可能不对。但是可以肯于的是libvirt获取machine是也是调用qemu的接口，所以会保持libvirt qemu的一致性。

如果中途切了qemu, 导致qemu os machine发生变化，重启下libvirt就可以了。

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