On a Monday in 2022, Daniel P. Berrangé wrote:
On Fri, Sep 23, 2022 at 05:42:13PM +0200, Peter Krempa wrote:
Introduce a new config option 'xml_validator' into the daemon config
file which will allow users to make libvirt daemons use a custom XML
validator.
The rationale is that validators such as 'jing'[1] provide drastically
better error specification when compared to the native libxml2 validator
we use. A drawback though is that jing is written in Java and thus
unusable by libvirt directly and also not a popular package present in
distros.
For power users and developers it still is worth having this feature to
provide better errors in a native way.
I kinda wonder if those users need it integrated in libvirt
though, as opposed to just calling jing themselves when
needed. It feels like a fairly narrow set of users benefitting
here from this change, made even smaller by the fact that those
users have to remember to reconfigure libvirt to enable this.
I would be more convinced if jing was still packaged for Fedora.
An example showing the quality of the errors:
XML used:
<vcpu placement='static' current='1'>asdf8</vcpu>
native validator:
error: XML document failed to validate against schema: Unable to validate doc against /home/pipo/libvirt/src/conf/schemas/domain.rng
Extra element vcpu in interleave
Invalid sequence in interleave
Element domain failed to validate content
jing:
error: XML document failed to validate against schema: Unable to validate doc against /home/pipo/libvirt/src/conf/schemas/domain.rng
/dev/stdin:6:52: error: character content of element "vcpu" invalid; must be an integer
No doubt the errors are way better, but a power user
can just invoke this script below themselves if they
ever want to understand a XML problem better.
Example script to make this feature work with jing:
#!/bin/bash
java -jar /home/pipo/git/jing-trang/build/jing.jar $1 /dev/stdin 2>&1 || exit 1
[1] https://github.com/relaxng/jing-trang
To me this is only compelling if there's an option we can reasonably
wire up out of the box.
Would switching to a different schema format make finding a validator
with frendlier messages easier?
Jano
With regards,
Daniel
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