[LTP] [PATCH v2] mmap01: fix check_file() test for file corruption

[Sven Schnelle]

mmap01 reported random test failures. Investigation showed
that check_file() will compare the whole buffer even if less
bytes were read from the file. Adjust check_file() to:

- fail the test if the not the correct amount of data has been read.
- only compare the bytes actually read

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
Changes in v2:

- check return value from SAFE_READ
- only verify bytes actually read

 testcases/kernel/syscalls/mmap/mmap01.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/testcases/kernel/syscalls/mmap/mmap01.c b/testcases/kernel/syscalls/mmap/mmap01.c
index c93c37ceda52..b5798c8d2367 100644
--- a/testcases/kernel/syscalls/mmap/mmap01.c
+++ b/testcases/kernel/syscalls/mmap/mmap01.c
@@ -35,15 +35,18 @@ static void check_file(void)
 {
 	int i, fildes, buf_len = sizeof(STRING) + 3;
 	char buf[buf_len];
+	ssize_t len;
 
 	fildes = SAFE_OPEN(TEMPFILE, O_RDONLY);
-	SAFE_READ(0, fildes, buf, sizeof(buf));
+	len = SAFE_READ(0, fildes, buf, sizeof(buf));
+	if (len != strlen(STRING))
+		tst_res(TFAIL, "Error reading from file\n");
 
-	for (i = 0; i < buf_len; i++)
+	for (i = 0; i < len; i++)
 		if (buf[i] == 'X' || buf[i] == 'Y' || buf[i] == 'Z')
 			break;
 
-	if (i == buf_len)
+	if (i == len)
 		tst_res(TPASS, "Specified pattern not found in file");
 	else
 		tst_res(TFAIL, "Specified pattern found in file");
-- 
2.47.1