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snap_flags = (libvirt.VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY |
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libvirt.VIR_DOMAIN_SNAPSHOT_CREATE_NO_METADATA |
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libvirt.VIR_DOMAIN_SNAPSHOT_CREATE_REUSE_EXT)
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QUIESCE = libvirt.VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE
-
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try:
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domain.snapshotCreateXML(snapshot_xml,
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snap_flags | QUIESCE)
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return
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except libvirt.libvirtError:
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LOG.exception(_LE('Unable to create quiesced VM snapshot, '
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'attempting again with quiescing disabled.'))
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try:
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domain.snapshotCreateXML(snapshot_xml, snap_flags)
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except libvirt.libvirtError:
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LOG.exception(_LE('Unable to create VM snapshot, '
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'failing volume_snapshot operation.'))
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- raise
它这里的逻辑是,先带VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE执行一遍,如果出错,再不带VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE flag执行,在libvirt过程中,VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE会在流程中加入通过qga接口冻结虚机文件系统的过程:
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/* If quiesce was requested, then issue a freeze command, and a
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* counterpart thaw command when it is actually sent to agent.
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* The command will fail if the guest is paused or the guest agent
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* is not running, or is already quiesced. */
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if (flags & VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE) {
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int freeze = qemuDomainSnapshotFSFreeze(driver, vm, NULL, 0);
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if (freeze < 0) {
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/* the helper reported the error */
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if (freeze == -2)
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thaw = -1; /* the command is sent but agent failed */
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goto endjob;
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}
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thaw = 1;
- }
这也是qemu链表式快照推荐的使用流程,参考 或 http://blog.chinaunix.net/uid-20940095-id-3588831.html
按字面意思来理解,尝试静默方式失败后,就应该是动静更大、更粗暴的方式咯,可是后一次尝试的flags组合确不会做暂停虚机等保护动作,直接调用qemu的blkdev-snapshot接口;所以对他这个做法有点疑问,希望高手指点,最后是libvirt对这个接口的一部分注释:
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If @flags includes VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY, then the
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snapshot will be limited to the disks described in @xmlDesc, and no
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VM state will be saved. For an active guest, the disk image may be
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inconsistent (as if power had been pulled), and specifying this
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with the VIR_DOMAIN_SNAPSHOT_CREATE_HALT flag risks data loss.
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If @flags includes VIR_DOMAIN_SNAPSHOT_CREATE_QUIESCE, then the
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libvirt will attempt to use guest agent to freeze and thaw all
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file systems in use within domain OS. However, if the guest agent
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is not present, an error is thrown. Moreover, this flag requires
- VIR_DOMAIN_SNAPSHOT_CREATE_DISK_ONLY to be passed as well.