[libvirt PATCH 0/2] Always validate XML for (hypervisor-)cpu-compare

[Peter Krempa]

On Thu, Apr 15, 2021 at 10:14:02 +0100, Daniel P. Berrangé wrote:
> On Thu, Apr 15, 2021 at 10:40:52AM +0200, Tim Wiederhake wrote:
> > XML schema validation for `virsh (hypervisor-)cpu-compare` has to be
> > enabled explicitly by passing the `--validate` flag. Having invalid
> > XML domain / cpu specification that appear to work can lead to hard
> > to find problems down the line, when e.g. migration of VMs does not
> > work as expected.
> > 
> > This series fixes a bug in the validation code and logs the schema
> > validation error to libvirtd's log file. User facing behaviour stays
> > unchanged.
> 
> I'm sceptical this is going to be beneficial. RNG validation error
> messages can be obscure at the best of times. I almost always need
> to look at the original input XML to understand what the RNG error
> really means. IOW just having the RNG error logged is unlikely to
> be enough to help people see what went wrong, assuming anyone even
> pays attention to the log.

And in addition to that (now speaking generally about also other APIs
which take XML and have voluntary validation) users can have a working
XML for their use case which may be invalid.

Spamming the logs in such case may be a double edged sword; in some
cases users might fix the XML if they notice something's wrong or in
other cases they may get their logs spammed with a irrelevant error.