[GitHub] [cloudstack] bwsw edited a comment on issue #3839: FEATURE-3823: kvm agent hooks

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bwsw edited a comment on issue #3839: FEATURE-3823: kvm agent hooks
URL: https://github.com/apache/cloudstack/pull/3839#issuecomment-588851139
 
 
   @andrijapanicsb 
   @svenvogel 
   
   ```groovy
   package groovy
   
   import com.sun.deploy.xml.XMLNode
   import groovy.util.XmlParser
   import groovy.util.Node
   import groovy.xml.XmlUtil
   
   class CacheDeviceAdder {
       def highSpeedDir = "/mnt/nvme0/"
       final def ramGBDivider = 1024
   
       Node diskXmlSpec(String swapFile) {
           return new XmlParser().parseText(
                   "    <disk type='file' device='disk'>\n" +
                   "      <driver name='qemu' type='qcow2' cache='none'/>\n" +
                   "      <source file='$swapFile'/>\n" +
                   "      <target dev='vdb' bus='ide'/>\n" +
                   "      <alias name='ide0-0-1'/>\n" +
                   "      <address type='drive' controller='0' bus='0' 
target='0' unit='1'/>\n" +
                   "    </disk>")
       }
   
       String transform(Object logger, String xml) {
           def vmDef = new XmlParser().parseText(xml)
           // get VM ram amount
           def memory = Integer.parseInt(vmDef.memory.text()) / ramGBDivider
           // get VM ram name
           def name = vmDef.name.text()
           def swapFile = highSpeedDir + name + ".qcow2"
           // remove swap device if exists
           "rm -f ${swapFile}".execute()
           def volCmd = "qemu-img create -f qcow2 ${swapFile} ${memory}G"
           // create new swap device
           volCmd.execute()
           def diskSpec = diskXmlSpec(swapFile)
           // update XML definition
           vmDef.devices[0].append(diskSpec)
           // return new XML definition
           return groovy.xml.XmlUtil.serialize(vmDef)
       }
   
       Object stop(Object logger, String vmName) {
           def swapFile = highSpeedDir + vmName.toString() + ".qcow2"
           // remove unused swap device
           "rm -f ${swapFile}".execute()
       }
   
       Object start(Object logger, String vmName) {
       }
   }
   
   new CacheDeviceAdder()
   ```
   
   This is a very simple hook which utilizes stop and transform cases:
   - When transform is used, it adds a highspeed volume which size is eq to VM 
RAM size, which can be used as a swap.
   - When stop, it removes an unused swap device from FS.
   - Start is not used, no idea how to use it in the current case.
   
   It's very primitive and avoids many checks, but allows getting a general 
idea.
   
   Again, I'll add the documentation, when somebody wants to approve the 
idea... Because, right now there is very simple documentation:
   
   - Configure hook paths and methods in the agent.properties
   - Implement hooks in the form: 
   
   ```groovy
   package groovy
   
   class AnyNameNoMatter {
          String method(Object logger, String xml) {
               return null // for onStart, onStop
               return xml // for xml transformation
         }
   }
   
   new AnyNameNoMatter()
   ```
   

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