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Re: [libvirt] [PATCH v2 14/21] conf: Shorten names in virDomainChrSerialTarget enumeration



On Fri, Nov 24, 2017 at 11:10:42 +0100, Andrea Bolognani wrote:
> On Thu, 2017-11-23 at 16:54 +0100, Pavel Hrdina wrote:
> > On Tue, Nov 21, 2017 at 05:42:24PM +0100, Andrea Bolognani wrote:
> > > Now that the target type is no longer formatted on the QEMU command
> > > line, we don't need the values to match the QEMU device names any
> > > longer, so we can shorten the names and reduce redundancy by dropping
> > > the -serial suffix: this also has the nice side-effect that target
> > > type and address type will now match.
> > > 
> > > We still need to parse the old names, and format them when preparing
> > > a migratable XML, to preserve backwards compatibility.
> > 
> > This would be probably nice to rename, but I'm afraid that we cannot
> > do that.  Even though you've made the effort to translate the old
> > name into new name if management application creates the XML using
> > the old name, the issue here is that it will no longer understand
> > what the new name means until the management application is updated.
> > Therefore this change is not backward compatible.
> 
> Is that so? virt-manager at least doesn't seem to have a problem
> with the change.
> 
> Any application that's been coded sensibly will deal with the new
> values in a graceful manner, eg. displaying "unknown model" or
> something along the line rather than failing.

Showing an unknown device and failing is not very different in this
case. The application adds a *-serial device and gets something else
back. We would need to format the old names in the XML everytime and not
in migratable XML only. So this would just add new shorter aliases apps
could use when talking to new libvirt. But they wouldn't use them anyway
because they would lose compatibility with older libvirt.

In other words, NACK to this patch.

Jirka


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