[libvirt] [PATCH 2/9] tests: qemuxml2xml: Always use different output file

[Laine Stump]

On 01/28/2016 03:30 PM, Cole Robinson wrote:
> Most qemuxml2xml tests expect that the input XML is unchanged after
> parsing. This is unlike 99% of new qemu configs in the wild, which after
> initial parsing end up with stable PCI device addresses. The xml2xml bit
> doesn't currently hit that code path though, so most XML testing indeed
> does not change.
>
> Future patches will add that PCI address bits, which means most test cases
> will have different output. So let's do away with the hardcoded same vs
> different test split, and always track a separate output file. Tests can
> still have same input and output, it just necessitates 2 separate XML files.
> ---
>   .../qemuxml2xmlout-aarch64-aavmf-virtio-mmio.xml   |  49 +++++

If there's going to be a ton of new files added anyway, this is a good 
chance to shorten the names of all the files (and avoid needing to do it 
to so many more files later). I've always thought it was pointless to 
have a file called

    qemuxml2xmloutdata/qemuxml2xmlout-blah.xml

why not just:

    qemuxml2xmloutdata/blah.xml

?? I recall there being problems with running make rpm (or maybe make 
distcheck?) because some filename in one of these directories was beyond 
the tarfile name length limit or something like that.

I went back and read Martin's opinion about adding all these files, and 
your response. It's true that we aren't *explicitly* testing the PCI 
address assignment directly in the xml2xml tests now. It does end up 
being tested in the xml2argvtests though (except for devices that are at 
fixed PCI addresses which don't show up on the qemu commandline, e.g.  
builtin IDE controller in 440fx or builtin SATA on q35). Of course it 
would be a lot easier to see what's going on if the XML files could be 
compared, rather than trying to compare qemu commandlines and 
backtracking to find the offending device in the XML :-)

Do you know what percentage of these files end up being different 
between source and result after all your changes are done? If it's 
all/most of them, then I think it would be a lot of extra effort for no 
gain to setup symbolic links now only to have them broken a few commits 
later.

(A bit of thinking out loud follows...)

Anyway, even once we add the PCI address assignment into the 
qemuxml2xmltest, we still may have a considerable number of tests that 
have the PCI address in the source xml already anyway. Also, I think too 
many of the tests have been created with the following formula:

1) copy testfiles for some random existing test
2) add on a line or two that tests the new feature

This has the upside of testing combinations of items that might not 
otherwise be tested, but there's nothing methodical about it, and we're 
ending up testing the same bits hundreds of times in exactly the same 
way. *AND* (the most important) if something is purposefully changed in 
one of those bits that is unnecessarily copied to a couple hundred tests 
(e.g. the output now has a PCI address in the element), then that change 
must be accompanied by changes to hundreds of test output files.

It might be useful to eliminate a bunch of this duplication of tests. 
But of course that would be *very* tedious, and the potential for 
accidentally removing a useful and unique combination would be high 
(especially if we fell to the temptation of letting a newcomer do such a 
trimming as a "starter" project).

(anyway...)

It would be nice if we could move all the tests that are there merely 
for checking genericxml2xml over to that test in advance of this change 
in order to reduce the churn, but I understand your reluctance to do 
that - it will involve a lot more subjective decisions about what was 
the purpose of various test cases (and for some of those the only clue 
you may have is the name of the data file), so it seems like a large 
annoying bookkeeping job when what you really need is to make ARM work 
correctly :-)

Since we already have hundreds of test files, and this seems to be 
moving in the right direction (although taking a nasty side-step), I'm 
inclined to ACK this patch. We should maybe put it to some kind of 
informal vote, though, just to make sure everyone's concerns are 
properly addressed (and maybe someone will come up with a bright idea)