syscalls/readahead02: fail test if readahead did not use any cache

The heuristic of failing the test only if not saving any io has false negatives with overlayfs readahead() bug, but readahead() with overlayfs always warns on "using less cache then expected", when actually, it is using no cache at all.

Add another condition to fail the test if readahead did not use any cache at all, which always detected the overlayfs bug.

Signed-off-by Amir Goldstein <[email protected]>

---

Cyril,

This is a followup for the overlayfs readahead series. With the patches already posted, the test fails sometimes, but most of the times it just gets a warning.

With this additional patch test fails reliably. Note that test only fails between these upstream commits:
good b833a3660394 ("ovl: add ovl_fadvise()")
bad 5b910bd615ba ("ovl: fix GPF in swapfile_activate...")

I have a few more minor fixes for the v2 series, but I will hold them back until v1 is reviewed.

Thanks,
Amir.

 testcases/kernel/syscalls/readahead/readahead02.c | 2 ++
 1 file changed, 2 insertions(+)

testcases/kernel/syscalls/readahead/readahead02.c +2 -1

index b497fb5db..fbcae1df8 100644
@@ -341,6 +341,8 @@ static void test_readahead(unsigned int n)
 		 */
 		if (cached_ra * 1024 > testfile_size / 2)
 			tst_res(TPASS, "using cache as expected");
+		else if (!cached_ra)
+			tst_res(TFAIL, "readahead failed to use any cache");
 		else
 			tst_res(TWARN, "using less cache than expected");
 	} else {
--

2.17.1

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