Re: [Qemu-devel] [PATCH v4 3/6] add backup related monitor commands

[Dietmar Maurer]

> > The management tooI just needs to convert the config - looks quite easy to
> me.
> 
> It's not an easy problem.  This is why there is no central vm-images.com where
> everyone can share/sell virtual appliances.  You cannot trivially convert 
> between
> VMware, oVirt, proxmox, Xen, EC2, etc.

For that case, I added the ability to write several different config files into 
a VMA archive.

So If someone want to distribute an appliance, he can simply add a config file 
for each manager.
 
> > > QEMU must provide the mechanism for point-in-time backups of block
> > > devices - your backup block job implements this.
> > >
> > > Where I disagree with this patch series is that you put the
> > > management tool- specific archive format writer into QEMU.  That is 
> > > outside
> the scope of QEMU.
> > > The management tool should tell QEMU to take the backups of block
> > > devices and do a live migration to file.
> > >
> > > The management tool can use a NBD server if it wants to capture all
> > > the block device backups into a single archive.  And the management
> > > tool can bundle the VM configuration into that archive too.  But
> > > those steps are beyond the scope of QEMU.
> > >
> > > The approach I'm suggesting is more modular.  For example, the
> > > backup block job can also be used to copy out the state of a disk
> > > into a new
> > > qcow2 file.
> >
> > OK, I can try to split the code. But I think I will simply define a
> > 'protocol' instead of using an NBD server (what for?)
> 
> block/nbd.c already exists so it saves you from writing the QEMU-side code to
> export data to another process.

Is there some documentation about that NBD protocol?

> The archive writer program opens a listen socket for each block device that is
> being backed up.  Then it handles NBD WRITE requests from QEMU.

I still think using a specific protocol is wrong. You don't want to use NDB if 
you can directly
talk to some backup server?