Re: [libvirt] [PATCH] tests: fix mocking of stat() / lstat() functions

Quite a few of the tests have a need to mock the stat() / lstat() functions and they are taking somewhat different & inconsistent approaches none of which are actually fully correct. This is shown by fact that 'make check' fails on 32-bit hosts. Investigation revealed that the code was calling into the native C library impl, not getting intercepted by our mocks. The POSIX stat() function might resolve to any number of different symbols in the C library. The may be an additional stat64() function exposed by the headers too. On 64-bit hosts the stat & stat64 functions are identical, always refering to the 64-bit ABI. On 32-bit hosts they refer to the 32-bit & 64-bit ABIs respectively. Libvirt uses _FILE_OFFSET_BITS=64 on 32-bit hosts, which causes the C library to transparently rewrite stat() calls to be stat64() calls. Libvirt will never see the 32-bit ABI from the traditional stat() call. We cannot assume this rewriting is done using a macro. It might be, but on GLibC it is done with a magic __asm__ statement to apply the rewrite at link time instead of at preprocessing. In GLibC there may be two additional functions exposed by the headers, __xstat() and __xstat64(). When these exist, stat() and stat64() are transparently rewritten to call __xstat() and __xstat64() respectively. The former symbols will not actally exist in the library at all, only the header. The leading "__" indicates the symbols are a private impl detail of the C library that applications should not care about. Unfortunately, because we are trying to mock replace the C library, we need to know about this internal impl detail. With all this in mind the list of functions we have to mock will depend on several factors - If _FILE_OFFSET_BITS is set, then we are on a 32-bit host, and we only need to mock stat64 and __xstat64. The other stat / __xstat functions exist, but we'll never call them so they can be ignored for mocking. - If _FILE_OFFSET_BITS is not set, then we are on a 64-bit host and we should mock stat, stat64, __xstat & __xstat64. Either may be called by app code. - If __xstat & __xstat64 exist, then stat & stat64 will not exist as symbols in the library, so the latter should not be mocked. The same all applies to lstat() These rules are complex enough that we don't want to duplicate them across every mock file, so this centralizes all the logic in a helper file virmockstathelper.c that should be #included when needed. The code merely need to provide a filename rewriting callback called virMockStatRedirect(). Optionally VIR_MOCK_STAT_HOOK can be defined as a macro if further processing is needed inline. Signed-off-by: Daniel P. Berrangé <berrange(a)redhat.com&gt; --- build-aux/mock-noinline.pl | 3 + cfg.mk | 4 +- tests/qemusecuritymock.c | 131 +++++----------- tests/vircgroupmock.c | 146 +++-------------- tests/virfilewrapper.c | 85 ++-------- tests/virmock.h | 11 -- tests/virmockstathelpers.c | 310 +++++++++++++++++++++++++++++++++++++ tests/virpcimock.c | 93 +---------- tests/virtestmock.c | 140 +---------------- 9 files changed, 396 insertions(+), 527 deletions(-) create mode 100644 tests/virmockstathelpers.c NB I have tested on Fedora 32-bit and 64-bit but have not yet tested on other platforms, so they may break. This is to be investigated before pushing so we don't break other platforms more than they are already broken wrt mocking :-)