On Fri, May 3, 2019 at 5:33 AM Logan Gunthorpe logang@deltatee.com wrote:
On 2019-05-03 12:48 a.m., Brendan Higgins wrote:
On Thu, May 2, 2019 at 8:15 PM Logan Gunthorpe logang@deltatee.com wrote:
On 2019-05-01 5:01 p.m., Brendan Higgins wrote:
+/*
- struct kunit_try_catch - provides a generic way to run code which might fail.
- @context: used to pass user data to the try and catch functions.
- kunit_try_catch provides a generic, architecture independent way to execute
- an arbitrary function of type kunit_try_catch_func_t which may bail out by
- calling kunit_try_catch_throw(). If kunit_try_catch_throw() is called, @try
- is stopped at the site of invocation and @catch is catch is called.
I found some of the C++ comparisons in this series a bit distasteful but wasn't going to say anything until I saw the try catch.... But looking into the implementation it's just a thread that can exit early which seems fine to me. Just a poor choice of name I guess...
Guilty as charged (I have a long history with C++, sorry). Would you prefer I changed the name? I just figured that try-catch is a commonly understood pattern that describes exactly what I am doing.
It is a commonly understood pattern, but I don't think it's what the code is doing. Try-catch cleans up an entire stack and allows each level of the stack to apply local cleanup. This implementation simply exits a thread and has none of that complexity. To me, it seems like an odd abstraction here as it's really just a test runner that can exit early (though I haven't seen the follow-up UML implementation).
Yeah, that is closer to what the UML specific version does, but that's a conversation for another time.
I would prefer to see this cleaned up such that the abstraction matches more what's going on but I don't feel that strongly about it so I'll leave it up to you to figure out what's best unless other reviewers have stronger opinions.
Cool. Let's revisit this with the follow-up patchset.
[snip]
+static void __noreturn kunit_abort(struct kunit *test) +{
kunit_set_death_test(test, true);kunit_try_catch_throw(&test->try_catch);/** Throw could not abort from test.** XXX: we should never reach this line! As kunit_try_catch_throw is* marked __noreturn.*/WARN_ONCE(true, "Throw could not abort from test!\n");+}
int kunit_init_test(struct kunit *test, const char *name) { spin_lock_init(&test->lock); @@ -77,6 +103,7 @@ int kunit_init_test(struct kunit *test, const char *name) test->name = name; test->vprintk = kunit_vprintk; test->fail = kunit_fail;
test->abort = kunit_abort;There are a number of these function pointers which seem to be pointless to me as you only ever set them to one function. Just call the function directly. As it is, it is an unnecessary indirection for someone reading the code. If and when you have multiple implementations of the function then add the pointer. Don't assume you're going to need it later on and add all this maintenance burden if you never use it..
Ah, yes, Frank (and probably others) previously asked me to remove unnecessary method pointers; I removed all the totally unused ones. As for these, I don't use them in this patchset, but I use them in my patchsets that will follow up this one. These in particular are present so that they can be mocked out for testing.
Adding indirection and function pointers solely for the purpose of mocking out while testing doesn't sit well with me and I don't think it should be a pattern that's encouraged. Adding extra complexity like this to a design to make it unit-testable doesn't seem like something that makes sense in kernel code. Especially given that indirect calls are more expensive in the age of spectre.
Indirection is a pretty common method to make something mockable or fakeable. Nevertheless, probably an easier discussion to have once we have some examples to discuss.
Also, mocking these particular functions seems like it's an artifact of how you've designed the try/catch abstraction. If the abstraction was more around an abort-able test runner then it doesn't make sense to need to mock out the abort/fail functions as you will be testing overly generic features of something that don't seem necessary to the implementation.
[snip]
+void kunit_generic_try_catch_init(struct kunit_try_catch *try_catch) +{
try_catch->run = kunit_generic_run_try_catch;try_catch->throw = kunit_generic_throw;+}
Same here. There's only one implementation of try_catch and I can't really see any sensible justification for another implementation. Even if there is, add the indirection when the second implementation is added. This isn't C++ and we don't need to make everything a "method".
These methods are for a UML specific implementation in a follow up patchset, which is needed for some features like crash recovery, death tests, and removes dependence on kthreads.
I know this probably sounds like premature complexity. Arguably it is in hindsight, but I wrote those features before I pulled out these interfaces (they were actually both originally in this patchset, but I dropped them to make this patchset easier to review). I can remove these methods and add them back in when I actually use them in the follow up patchsets if you prefer.
Yes, remove them now and add them back when you use them in follow-up patches. If reviewers find problems with the follow-up patches or have a better suggestion on how to do what ever it is you are doing, then you just have this unnecessary code and there's wasted developer time and review bandwidth that will need to be spent cleaning it up.
Fair enough. Next patchset will have the remaining unused indirection you pointed out removed.
Thanks!