[PATCH] generic/574: fix sporadic failure with test_dummy_encryption

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

When the "test_dummy_encryption" mount option is specified, the
fs-verity file corruption test generic/574 is flaky; it fails about 1%
of the time.  This happens because in the three test cases where a
single byte of the test file is corrupted, sometimes the new byte
happens to be the same as the original.  This is specific to
test_dummy_encryption because the encrypted data is nondeterministic
(and appears random), unlike the unencrypted data.

Fix this by corrupting 5 bytes instead of 1, so that the probability of
failure becomes effectively zero.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 tests/generic/574     | 11 ++++++++---
 tests/generic/574.out |  6 +++---
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/tests/generic/574 b/tests/generic/574
index 246f0858..da776a24 100755
--- a/tests/generic/574
+++ b/tests/generic/574
@@ -135,10 +135,15 @@ corruption_test()
 	fi
 }
 
-corruption_test 131072 0 1
-corruption_test 131072 4095 1
+# Note: these tests just overwrite some bytes without checking their original
+# values.  Therefore, make sure to overwrite at least 5 or so bytes, to make it
+# nearly guaranteed that there will be a change -- even when the test file is
+# encrypted due to the test_dummy_encryption mount option being specified.
+
+corruption_test 131072 0 5
+corruption_test 131072 4091 5
 corruption_test 131072 65536 65536
-corruption_test 131072 131071 1
+corruption_test 131072 131067 5
 
 # Non-zeroed bytes in the final partial block beyond EOF should cause reads to
 # fail too.  Such bytes would be visible via mmap().
diff --git a/tests/generic/574.out b/tests/generic/574.out
index 5b304c83..d43474c5 100644
--- a/tests/generic/574.out
+++ b/tests/generic/574.out
@@ -1,6 +1,6 @@
 QA output created by 574
 
-# Corruption test: file_len=131072 zap_offset=0 zap_len=1
+# Corruption test: file_len=131072 zap_offset=0 zap_len=5
 0dfbe8aa4c20b52e1b8bf3cb6cbdf193  SCRATCH_MNT/file.fsv
 Corrupting bytes...
 Validating corruption (reading full file)...
@@ -14,7 +14,7 @@ Bus error
 Validating corruption (reading just corrupted part via mmap)...
 Bus error
 
-# Corruption test: file_len=131072 zap_offset=4095 zap_len=1
+# Corruption test: file_len=131072 zap_offset=4091 zap_len=5
 0dfbe8aa4c20b52e1b8bf3cb6cbdf193  SCRATCH_MNT/file.fsv
 Corrupting bytes...
 Validating corruption (reading full file)...
@@ -42,7 +42,7 @@ Bus error
 Validating corruption (reading just corrupted part via mmap)...
 Bus error
 
-# Corruption test: file_len=131072 zap_offset=131071 zap_len=1
+# Corruption test: file_len=131072 zap_offset=131067 zap_len=5
 0dfbe8aa4c20b52e1b8bf3cb6cbdf193  SCRATCH_MNT/file.fsv
 Corrupting bytes...
 Validating corruption (reading full file)...
-- 
2.28.0