Re: [libvirt] [Xen-devel] [PATCH 0/5] Testing libvirt XML -> libxl_domain_config conversion
On Fri, 2014-05-30 at 18:24 +0100, Daniel P. Berrange wrote:
At the Xen Hackathon I learnt that libxl provides an API which
can serialize a libxl_domain_config instance to a JSON document.
This is exactly what we need for testing the XML -> libxl_domain_config
conversion process, so I spent the afternoon trying to get such a test
working. The result is that we can now just add pairs of XML, JSON
files to libvirt to test handling of new config features.
I hit a couple of small issues with libxl, which I worked around, when
writing this test which I why I'm copying xen-devel
- libxl_ctx_alloc() will call xs_daemon_open and xc_interface_open,
and stat /var/run/xenstored.pid to see if Xen is actually running.
This fails when run on non-Xen hosts (and also possibly if run
unprivileged).
I used an evil LD_PRELOAD hack to stub out xs_daemon_open and
xc_interface_open to return (void*)0x1, and also turn
xc_interface_close and xs_daemon_close to no-ops, and make
stat() always return success for xenstored.pid.
This works (evidenced by the fact that if something was needing
these xs/xc handles they would have crashed referencing 0x1),
but at the same time it might be an idea to have an officially
supported "non live" mode for libxl_ctx_alloc() turned on by a
flag of some sort.
Yes, we absolutely should have this.
- The libxl_json.h header file is relying on conditionals that
are only set by Xen's build process
eg HAVE_YAJL_YAJL_VERSION_H
It looks like this header has ended up with a mixture of library
internal and user facing stuff, which is wrong. I think splitting the
internal stuff into libxl_json_internal.h or similar would solve this.
I'll take a look.
I hacked around this, but it is a little dirty too. libvirt
already links to libyajl for the QEMU driver, but we don't
really need the raw YAJL objects. It'd be nice to have a
char * libxl_domain_config_as_json(libxl_domain_config *p)
as a higher level wrapper around libxl_domain_config_gen_json
avoiding the pain of dealing with YAJL's different APIs.
Ian J mentioned to me that he thought there was already such a
method, but AFAICT, the only such code is in the 'xl' command
line tool itself (xl_cmdimpl.c - printf_info_one_json)
That was me not Ian J I think.
The function you need is libxl_domain_config_to_json (which is
autogenerated, so in _libxl_types.[hc]). I think the general
libxl_*_to_json support has been there since Xen 4.2, but IIRC
libxl_domain_config only got moved into the autogenerated/IDL layer in
4.3.
For compatibility with 4.2 you could probably use libxl_*_to_json on the
various members of libxl_domain_config individually, or just punt on the
unit tests in that case of course...
Ian.