[libvirt] [PATCH 08/10] libxl: support domain config modification in virDomainRestoreFlags

[Marek Marczykowski-Górecki]

On Thu, Feb 19, 2015 at 11:59:38AM -0700, Jim Fehlig wrote:
> Marek Marczykowski-Górecki wrote:
> > Signed-off-by: Marek Marczykowski-Górecki <marmarek at invisiblethingslab.com>
> > ---
> >
> > There was a discussion about calling virDomainDefCheckABIStability. The use
> > case I have for this is to start multiple domains from the same savefile.
> 
> Interesting use case...

If you're curious about details, it is used for DisposableVMs in Qubes
OS:
http://theinvisiblethings.blogspot.com/2010/06/disposable-vms.html

Basically to speedup domain startup (with some preloaded applications
etc). Domain state is discarded after its termination (disk image is
read-only).

> >  This require changing:
> >  - UUID
> >  - name
> >  - IP address
> >   
> 
> Did you mean mac address?  I don't see where the
> virtDomain*CheckABIStability() functions check for changes to IP addresses.

Of course, I mean MAC address (in addition to IP address).

> > Those are exactly type of changes blocked by virDomainDefCheckABIStability.
> > Perhaps some "permissive" mode should be introduced to the
> > virDomainDefCheckABIStability function?
> >   
> 
> I'd like to hear what others think about this proposal.  Are UUID and
> name really part of a domain's ABI?

At least by the implementation of virDomainDefCheckABIStability...
Comment says this is to not confuse domain during migration.

> Regards,
> Jim
> 
> >  src/libxl/libxl_driver.c | 17 ++++++++++++-----
> >  1 file changed, 12 insertions(+), 5 deletions(-)
> >
> > diff --git a/src/libxl/libxl_driver.c b/src/libxl/libxl_driver.c
> > index 005cc96..7539d33 100644
> > --- a/src/libxl/libxl_driver.c
> > +++ b/src/libxl/libxl_driver.c
> > @@ -1456,11 +1456,6 @@ libxlDomainRestoreFlags(virConnectPtr conn, const char *from,
> >  #endif
> >  
> >      virCheckFlags(VIR_DOMAIN_SAVE_PAUSED, -1);
> > -    if (dxml) {
> > -        virReportError(VIR_ERR_ARGUMENT_UNSUPPORTED, "%s",
> > -                       _("xml modification unsupported"));
> > -        return -1;
> > -    }
> >  
> >      fd = libxlDomainSaveImageOpen(driver, cfg, from, &def, &hdr);
> >      if (fd < 0)
> > @@ -1469,6 +1464,18 @@ libxlDomainRestoreFlags(virConnectPtr conn, const char *from,
> >      if (virDomainRestoreFlagsEnsureACL(conn, def) < 0)
> >          goto cleanup_unlock;
> >  
> > +    if (dxml) {
> > +        virDomainDefPtr def2 = NULL;
> > +
> > +        if (!(def2 = virDomainDefParseString(dxml, cfg->caps, driver->xmlopt,
> > +                                        1 << VIR_DOMAIN_VIRT_XEN,
> > +                                        VIR_DOMAIN_XML_INACTIVE))) {
> > +            goto cleanup;
> > +        }
> > +        virDomainDefFree(def);
> > +        def = def2;
> > +    }
> > +
> >      if (!(vm = virDomainObjListAdd(driver->domains, def,
> >                                     driver->xmlopt,
> >                                     VIR_DOMAIN_OBJ_LIST_ADD_LIVE |
> >   

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
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