On Fri, Oct 21, 2022, Vitaly Kuznetsov wrote: > Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> writes: > > > Sean Christopherson <seanjc@xxxxxxxxxx> writes: > >> Do you happen to know if errno is preserved? I.e. if TEST_ASSERT()'s print of > >> errno will capture the right errno? If so, this and the pthread_join() assert > >> can be: > >> > >> TEST_ASSERT(!r, pthread_cancel() failed on vcpu_id=%d, vcpu->id); > >> > > > > The example from 'man 3 pthread_cancel' makes me think errno is not > > set. 'man 3 errno' confirms that: > > > > " > > Note that the POSIX threads APIs do not set errno on error. Ah, that's annoying. > > Instead, on failure they return an error number as the function result. > > These error numbers have the same meanings as the error numbers returned > > in errno by other APIs. > > " > > > > but nothing stops us from doing something like > > > > #include <errno.h> > > ... > > > > errno = pthread_cancel(thread); > > TEST_ASSERT(!errno, pthread_cancel() failed on vcpu_id=%d, vcpu->id); > > > > I believe. > > ... only the fact that this won't be thread safe :-( i.e. if we also try > setting 'errno' from vcpu_thread() (where the pattern for > pthread_setcanceltype() is exactly the same), we will likely be > reporting the wrong errno. errno is thread safe. From https://man7.org/linux/man-pages/man3/errno.3.html: errno is defined by the ISO C standard to be a modifiable lvalue of type int, and must not be explicitly declared; errno may be a macro. errno is thread-local; setting it in one thread does not affect its value in any other thread. > I think it's better to keep reporting 'r' for now (and maybe think about > pthread* wrappers later). Yeah, definitely a future problem. pthread wrappers are a good idea, I doubt there's a single KVM selftest that wants to do anything but assert on failure.
