[libvirt] [re-send][PATCH 1/3] add qemu driver hook

[li guang]

在 2012-10-08一的 21:54 -0600，Eric Blake写道：
> On 10/08/2012 08:33 PM, li guang wrote:
> > 在 2012-10-08一的 20:05 -0600，Eric Blake写道：
> >> On 10/08/2012 07:51 PM, liguang wrote:
> >>> this hook aimed at migration only, it supposed
> >>> to be used as a helper of migrate --copy-storage-*
> >>> features to remove the unreasonable limitation
> >>> of pre-exist disk images at migration target.
> >>> someone can add more functions to hook files.
> >>
> >> NACK.  Instead of writing a hook that runs outside of libvirt and has to
> >> be installed to be of use, we should instead fix libvirt to do the file
> >> creation itself.  That is, you should be patching
> >> src/qemu/qemu_migration.c to detect when copy-storage-* has been passed,
> > 
> > really? sorry, I don't know any implicit libvirt development rules,
> > but, as I see, there are none hooks used by libvirt until now, why 
> > don't we use them instead of just design and obsolete?
> 
> The problem with doing this as a python hook instead of directly in the
> libvirt code is that you still got the sVirt SELinux labeling wrong.
> Really, the file MUST be created by the libvirt C code, as that is the
> code that knows what SELinux label to apply to the new file.
> Furthermore, hooks are reserved for the user.  We should not be making
> libvirt rely on the installation of hooks for correct operation of the
> normal case.
> 
> > can't hooks be installed just like other libvirt files?
> > then, create files by python or c have difference?
> 
> Hooks are limited in what they can do - they are documented as being
> unable to call back in to other libvirt calls.  They are also less
> efficient - why spawn a python process, when we already have all the
> information to create the file in C code?
> 
> Ultimately, I'd like to see this wart of --copy-storage fixed, but fixed
> properly in the C code and not by adding a hook file.
> 

OK, I see, thanks a lot!

-- 
liguang    lig.fnst at cn.fujitsu.com
FNST linux kernel team