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

[Dietmar Maurer]

> >> What I am looking for is a stripped down patch series with just a
> >> backup block job (no backup archive writer or migration code).  That
> >> would be easily merged and saves you front rebasing this series as QEMU
> changes.
> >
> > That is Patch 2/6?
> 
> Yes.  I sent an RFC series that shows this approach.  It is just a prototype 
> but it
> demonstrates that the NBD approach works and performs reasonably well for a
> quick Python hack.
> 
> The stripped down patch series needs:
> 1. (Optional) query-block virtual_size field if management tool needs to query
> drive size 2. Patch 2/6 with review comments addressed 3. 'block-backup' QMP
> command (and optionally HMP command)
> 
> That's it!

Thanks. I also have an  implementation here using that approach (using nbd.c).
The problem is the performance you get. 28% delay is not acceptable.

In fact, I want to have the fastest possible solution (additional delay = 0).

You want to move the code out of qemu, so that management frameworks
can easily plug their own backup tools. That is perfectly valid, but we should 
do
it in a way that does not influence performance.

So are there any other ideas?