VM Screenshot

Summary

Allow users to take screenshot of a running VM

Owner

• Name: Saif Abu Saleh (sabusale)

Description

Users need a way to see the current state of their VMs for debug purposes, when they don’t have console access

UI

Not supported

VDSM

VDSM will call Libvirt screenshot API [2]

Libvirt will call QEMU to capture the screenshot

then VDSM will return ppm file content as base64 string

Backend

Backend will call VDSM to capture screenshot and will receive base64 string screenshot and then base64 string will be converted to byte array and returned

REST API

Rest API will call Backend to capture the screenshot

Rest API call is synchronous operation

Rest API implementation is intended for debugging only

API call Example:

/vms/{vm:id}/screenshot

      POST /vms/1234/screenshot
      Accept: application/xml

Response is a byte array of the screenshot

iVBORw0K..

Image format issues

ppm is not a standard screenshot format, and users may have issues to see the screenshot, and it is not straight forward to display it in HTML[4], unlike e.g. png base64

issue[5] opened to QEMU to add screen dump as PNG

other option is to convert the ppm content to other standard format like png ways to convert it:

• Convert it in VDSM using PIL image library: example
• In Engine use java API to convert it using ImageMagick

Future work

• Add the functionality to web UI

• Libvirt screenshot API provides option to capture screenshot by screen number (in case there are multiple screens).

  for now by default 0 only used(first screen), add the option to take screenshot by screen number

• Change generate screenshot API call to be asynchronous