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Re: [libvirt] [PATCH 0/3] libxl: Add a test suite for libxl_domain_config generator



On Thu, Jul 27, 2017 at 03:24:38PM -0600, Jim Fehlig wrote:
> On 07/26/2017 05:07 PM, Marek Marczykowski-Górecki wrote:
> > On Fri, Jul 14, 2017 at 05:59:57PM -0600, Jim Fehlig wrote:
> > > On 07/01/2017 08:16 PM, Marek Marczykowski-Górecki wrote:
> > > > On Sun, Feb 26, 2017 at 07:02:24PM -0700, Jim Fehlig wrote:
> > > > > Long ago danpb posted some patches to test libvirt domXML to
> > > > > libxl_domain_config conversion
> > > > > 
> > > > > https://www.redhat.com/archives/libvir-list/2014-May/msg01102.html
> > > > > 
> > > > > Some of the prerequisite patches were pushed, but we've never managed
> > > > > to push patches actually providing the conversion tests. I sent several
> > > > > follow-ups to Dan's work but never converged on a satisfactory solution
> > > > > for all the Xen versions supported by libvirt. The last attempt was in
> > > > > Sept 2014
> > > > > 
> > > > > https://www.redhat.com/archives/libvir-list/2014-September/msg00698.html
> > > > > 
> > > > > I tried to revive the work in Jan 2015, but that also stalled
> > > > > 
> > > > > https://www.redhat.com/archives/libvir-list/2015-January/msg00924.html
> > > > > 
> > > > > Fast-forward over 2.5 years from the first attempt and libvirt no longer
> > > > > supports older Xen versions 4.2 and 4.3 that were proving to be problematic.
> > > > > Starting with Xen 4.5 libxl added support for libxl_domain_config_from_json,
> > > > > which provides a way to implement the conversion tests that work with all
> > > > > Xen versions >= 4.5 (including latest xen.git master).
> > > > 
> > > > Few more months have passed...
> > > 
> > > And a few more weeks :-). Sorry for the delay. Slowly catching up on libvirt
> > > mail after some time away...
> > 
> > It's me this time...
> > 
> > > > FWIW, I've tested it with Xen 4.6. The patch needs very minor update:
> > > >    - s/VIRT_TEST_MAIN_PRELOAD/VIR_TEST_MAIN_PRELOAD/
> > > >    - add xencaps argument to libxlBuildDomainConfig cal >
> > > > 
> > > > After that, it works! When I made some test to fail, reported error is
> > > > not so helpful ("libvirt: Xen Light Driver error : internal error:
> > > > Expected and actual libxl_domain_config objects do not compare"), but it
> > > > do catch failures.
> > > > Then, if I change strcmp to virTestCompareToString, the output is much
> > > > more helpful.
> > > 
> > > Thanks for the improvements. I noticed you included them in your V2 of patch
> > > 3/3. I assume you needed patches 1 and 2 as well?
> > 
> > Yes, in this tests shape. But see below.
> > 
> > > > I'd really love to have it merged, mostly because I want to add more tests
> > > > using this framework (see "Add setting CPU features (CPUID) with
> > > > libxenlight driver" thread).
> > > 
> > > I really dislike patches 1 and 2. They remove very useful checks IMO.
> > > Shortly after posting the series in Feb, I tried mocking the emulator
> > > checks. I failed quite a bit before coming up with something that worked,
> > > yet not so satisfying :-). I'll attach the (now rather old) patches for
> > > reference.
> > 
> > My independent try to this test approach ("tests: check domain XML to
> > libxl structures conversion") had much simpler (but uglier) solution for
> > this problem: use /bin/true as emulator path (replaced in runtime, just
> > after loading XML from file).
> 
> Ah, clever and devious. For that matter all the test files could be changed
> to <emulator>/bin/true</emulator> :-).
> 
> > > Do you have time to update these old patches, test, and repost to the list?
> > > Or perhaps have better ideas on mocking, or approaches that avoid the need
> > > for 1/3 and 2/3.
> > 
> > If using /bin/true as emulator path is acceptable, I can finish this and
> > post updated version.
> 
> Did you have any comment on the approach taken in the attachments to this
> thread? Particularly the patch titled "libxl: make emulator checks
> mockable"?

I don't see how macros could solve this - those are expanded at
individual files compilation time. And you don't recompile the driver
for tests.
Something that could work would be putting those two functions into
separate shared object, then override using LD_PRELOAD or something like
this. But it would require significant change in the driver structure
just for tests. Alternatively something similar could be done by
covering lower level functions (virFileExists, virCommandRun, or even
open, stat etc).
Using /bin/true is much simpler anyway.

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?

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