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

[Kevin Wolf]

Am 19.09.2013 um 14:55 hat Benoît Canet geschrieben:
> Le Thursday 19 Sep 2013 à 10:57:50 (+0200), Kevin Wolf a écrit :
> > Am 19.09.2013 um 10:26 hat Stefan Hajnoczi geschrieben:
> > > 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
> > 
> > By the way, I think he concrete syntax might have to be a bit different
> > so it can be mapped to QAPI for blockdev-add. I think we'll want to use
> > a JSON list for the children; a mapping to QDict and to the command line
> > is yet to be implemented I guess.
> 
> Hi,
> 
> Just to make sure I'll code the right thing; is the following correct ?
> 
> -drive if=none,file.driver=quorum,format=raw,\
>        file.children=[/nfs1/test.qcow2, /nfs2/test.qcow2, /nfs3/test.qcow2], \
>        file.vote_threshold=2

I was thinking more along the lines of:

    -drive if=none,file.driver=quorum,format=raw,\
           file.children[0].file.filename=/nfs1/test.qcow2, \
           file.children[1].file.filename=/nfs2/test.qcow2, \
           file.children[1].file.cache.direct=on, \
           file.children[2].file.driver=nbd, \
           file.children[2].file.host=localhost, \
           file.vote_threshold=2

The exact syntax doesn't matter all that much as long as it can be
mapped to QAPI, but as you can see this allows specifying detailed
options even for the children. I think this is a requirement.

Kevin