[M] Change in flashrom[master]: tests: Detect gcov file io and unmock io functions

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Evan Benn.

Anastasia Klimchuk has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/69266 )

Change subject: tests: Detect gcov file io and unmock io functions
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Patch Set 6:

(5 comments)

Commit Message:

https://review.coreboot.org/c/flashrom/+/69266/comment/aab6a688_5a3a70bc 
PS6, Line 9: atexit
missing space: atexit -> at exit

Patchset:

PS6: 
I suggest this patch can be split into 3 patches:
1) Adding two new iom_* custom mocks and calling them from tests.c
2) Implementing coverage.c with unwraps, real_io, check_suffix and anything else needed for coverage (probably includes __real_* wraps too)
3) Calling handle_coverage call into mock_open.

1) ans 2) are no-op , the last patch 3) changes the behaviour.

File tests/io_mock.h:

https://review.coreboot.org/c/flashrom/+/69266/comment/4f52fdef_a2862fae 
PS6, Line 110: 	size_t (*iom_fwrite)(void *state, const void *buf, size_t size, size_t len, FILE *fp);
Adding these (iom_fwrite and iom_fdopen) two can go into a separate patch, together with their callsites in tests.c

File tests/tests.c:

https://review.coreboot.org/c/flashrom/+/69266/comment/7ff0aa43_d9238b70 
PS6, Line 52: real_io_mock
I think you can drop _mock, this is just real_io

https://review.coreboot.org/c/flashrom/+/69266/comment/a4436626_5391c09b 
PS6, Line 29: static int unwrap_open(void *state, const char *pathname, int flags, mode_t mode)
            : {
            : 	LOG_ME;
            : 	(void)state;
            : 	return __real_open(pathname, flags, mode);
            : }
            : 
            : static FILE *unwrap_fdopen(void *state, int fd, const char *mode)
            : {
            : 	LOG_ME;
            : 	(void)state;
            : 	return __real_fdopen(fd, mode);
            : }
            : 
            : static size_t unwrap_fwrite(void *state, const void *ptr, size_t size, size_t nmemb, FILE *fp)
            : {
            : 	LOG_ME;
            : 	(void)state;
            : 	return __real_fwrite(ptr, size, nmemb, fp);
            : }
            : 
            : // Mock ios that defer to the real io functions.
            : // These exist so that code coverage can print to real files on disk.
            : static const struct io_mock real_io_mock = {
            : 	.iom_open = unwrap_open,
            : 	.iom_fwrite = unwrap_fwrite,
            : 	.iom_fdopen = unwrap_fdopen,
            : };
Ideally, if this could go to a separate file for example `coverage.c` which would only expose one function: `handle_coverage` (name is my suggestion). This function will be called in `mock_open`.
The rest of code is inside coverage.c: all unwraps, real_io, check_suffix and anything else coverage specific.