Re: [Libvir] Relative paths in domain XML
On Sun, Apr 13, 2008 at 09:28:59AM +0100, Richard W.M. Jones wrote:
What would be really useful is to allow paths (eg. to file-backed
block devices) to be relative in a useful way. This would let you
have the domain XML configuration file & the block device files sit
next to each other to give a machine description:
mydomain.hda.img
mydomain.xml # refers to <source file="mydomain.hda.img">
This isn't possible at the moment as far as I can tell, which means
you need to know which directory the files are located in, and you
can't move them around.
Having relative paths to disk files in the XML isn't useful because
the drivers make no guarentees about where the XML files will be
stored - if indeed they're stored at all. Full-qualified paths to
disks are the only sensible option for domain XML IMHO.
[As an aside, at present the QEMU driver makes no attempt to check
that the source file is an absolute path, it just passes whatever it
finds to the '-hdc' argument to qemu.]
For the command:
virsh define mydomain.xml
One implementation would be to have virsh rewriting paths, but that
requires special knowledge of the XML format in virsh so I don't think
it's a workable idea. Another would be to allow virsh to supply a
'base URI' (basically, the current directory) to the
virDomainDefineXML call.
Any thoughts?
I think this is mixing up two concepts really - the domain XML is used
to represent a specific instantiation of a domain and as such it should
fully specify things like paths.
The use case of keeping disk images & XML alongside each other is really
in the realms of appliance images. The virt-image tool provides a format
for describing appliances and does support having relative paths. It then
turns this into the domain XML for the specific instantiation using a
fully qualfied path.
Dan.
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