Re: [Qemu-devel] Merging the quorum block driver

[Stefan Hajnoczi]

On Wed, Sep 18, 2013 at 05:05:27PM +0200, Benoît Canet wrote:
> Le Tuesday 17 Sep 2013 à 14:44:13 (+0200), Stefan Hajnoczi a écrit :
> > Hi Benoit,
> > Kevin and I had a chance to chat face-to-face and we discussed what
> > concrete changes are necessary to merge quorum (without solving all the
> > other block layers problems at once).
> > 
> > I think quorum could be merged relatively quickly (and without massive
> > BlockFilter investments) by changing the following:
> > 
> > 1. Defining children on the command-line
> > 
> > Existing "filter" drivers use the protocol filename to embed their
> > children, for example the blkverify driver.  This is a big hack because
> > we have no proper syntax or escaping for the embedded drive definitions
> > in the file= option.
> > 
> > This was one of the main arguments against merging quorum.  Now that
> > Kevin has implemented driver-specific open options (see
> > block/qcow2.c:qcow2_runtime_opts), it is possible for the quorum driver
> > to open children specific on the command-line:
> > 
> >   -drive if=none,file.driver=quorum,format=raw,\
> >          file.children0.file=/nfs1/test.qcow2,\
> >          file.children1.file=/nfs2/test.qcow2,\
> >          file.children2.file=/nfs3/test.qcow2
> 
> Hello Stefan,
> 
> I started writing the code.
> 
> How would the quorum treshold be specified with this command line style ?

Kevin can correct me but I think:

  -drive ...,file.vote_threshold=2

BlockDrivers can have custom options.  The voting threshold is a good
example.

quorum_open() can check for "vote_threshold" in its options qdict.

Stefan