Re: Google Summer of Code 2014 - Rewriting Virtual-Box Driver

Laine Stump <laine@xxxxxxxxx> · Tue, 11 Mar 2014 10:29:45 -0600



    On 03/11/2014 08:35 AM, prashanth
      sunder wrote:

    
                        Hello,

                        
                      I am applying for the project idea "Rewriting
                      Virtual-Box Driver" suggested by Michal Privoznik(mprivozn@xxxxxxxxxx)
                      in the "Qemu" ideas page (http://wiki.qemu.org/Google_Summer_of_Code_2014).
                      

                      In the short span of time that I had after my
                      discussion with Mr. Privoznik, the current Virtual
                      Box driver code is not structured very well(lot of
                      #ifdef's in the current code) and very hard to
                      read. 

                      
                      Since libvirt has to support all versions of
                      Virtual Box, the current code decides on what code
                      to compile based on the value of the macro 

                      VBOX_API_VERSION 

                      
                      that is checked during ./configure. 

                      
                    The only thing after discussion that we were able to
                    come up with is putting 

                  
                  version specific code under particular files and only
                  compile the those necessary 

                
                files during "make"

                
              For instance, 

              if a function X() supports version A, B, C we will have
              function X() in vbox_A.c just for version A, function X()
              in vbox_B.c just for version B and so on.

              
            Any other suggestions than the above mentioned one which 

            can be used to fix the problem??

          
    Just a couple things off the top of my head (keeping in mind that
    I've never actually used virtual box or the virtual box driver, but
    only have suffered the pain of reviewing a few virtualbox driver
    patches :-)

    
    1) I recall that there is a lot of *almost* identical code for the
    various versions. Rather than just moving those nearly identical
    pieces of code into different files for each version, it would make
    maintenance simpler if the essence of the difference between
    versions could be extracted into smaller lower-level functions that
    had as little shared code as possible, and were called from common
    top-level functions.

    
    2) If possible, it would be nice if the code for all versions of
    virtualbox was always compiled, and the decision of which set of
    functions to use was made at runtime. (Basically, each incompatible
    vbox version would have a separate "backend driver" in libvirt
    parlance, and the dispatch table for the backend drivers would
    essentially be the list of low-level functions from item (1)). This
    way it would be possible to upgrade to a new virtualbox version
    without requiring a lock-step update to a libvirt that had been
    compiled for the new virtualbox version.

    
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