[PATCH v4] riscv: selftests: Fix warnings pointer masking test

[Charlie Jenkins <charlie@xxxxxxxxxxxx>]

When compiling the pointer masking tests with -Wall this warning
is present:

pointer_masking.c: In function ‘test_tagged_addr_abi_sysctl’:
pointer_masking.c:203:9: warning: ignoring return value of ‘pwrite’
declared with attribute ‘warn_unused_result’ [-Wunused-result]
  203 |         pwrite(fd, &value, 1, 0); |
      ^~~~~~~~~~~~~~~~~~~~~~~~ pointer_masking.c:208:9: warning:
ignoring return value of ‘pwrite’ declared with attribute
‘warn_unused_result’ [-Wunused-result]
  208 |         pwrite(fd, &value, 1, 0);

I came across this on riscv64-linux-gnu-gcc (Ubuntu
11.4.0-1ubuntu1~22.04).

Fix this by checking that the number of bytes written equal the expected
number of bytes written.

Fixes: 7470b5afd150 ("riscv: selftests: Add a pointer masking test")
Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
---
Changes in v4:
- Skip sysctl_enabled test if first pwrite failed
- Link to v3: https://lore.kernel.org/r/20241205-fix_warnings_pointer_masking_tests-v3-1-5c28b0f9640d@xxxxxxxxxxxx

Changes in v3:
- Fix sysctl enabled test case (Drew/Alex)
- Move pwrite err condition into goto (Drew)
- Link to v2: https://lore.kernel.org/r/20241204-fix_warnings_pointer_masking_tests-v2-1-1bf0c5095f58@xxxxxxxxxxxx

Changes in v2:
- I had ret != 2 for testing, I changed it to be ret != 1.
- Link to v1: https://lore.kernel.org/r/20241204-fix_warnings_pointer_masking_tests-v1-1-ea1e9665ce7a@xxxxxxxxxxxx
---
 tools/testing/selftests/riscv/abi/pointer_masking.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/riscv/abi/pointer_masking.c b/tools/testing/selftests/riscv/abi/pointer_masking.c
index dee41b7ee3e3..759445d5f265 100644
--- a/tools/testing/selftests/riscv/abi/pointer_masking.c
+++ b/tools/testing/selftests/riscv/abi/pointer_masking.c
@@ -189,6 +189,8 @@ static void test_tagged_addr_abi_sysctl(void)
 {
 	char value;
 	int fd;
+	int ret;
+	char *err_pwrite_msg = "failed to write to /proc/sys/abi/tagged_addr_disabled\n";
 
 	ksft_print_msg("Testing tagged address ABI sysctl\n");
 
@@ -200,18 +202,32 @@ static void test_tagged_addr_abi_sysctl(void)
 	}
 
 	value = '1';
-	pwrite(fd, &value, 1, 0);
+	ret = pwrite(fd, &value, 1, 0);
+	if (ret != 1) {
+		ksft_test_result_skip(err_pwrite_msg);
+		goto err_pwrite;
+	}
+
 	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == -EINVAL,
 			 "sysctl disabled\n");
 
 	value = '0';
-	pwrite(fd, &value, 1, 0);
+	ret = pwrite(fd, &value, 1, 0);
+	if (ret != 1)
+		goto err_pwrite;
+
 	ksft_test_result(set_tagged_addr_ctrl(min_pmlen, true) == 0,
 			 "sysctl enabled\n");
 
 	set_tagged_addr_ctrl(0, false);
 
 	close(fd);
+
+	return;
+
+err_pwrite:
+	close(fd);
+	ksft_test_result_fail(err_pwrite_msg);
 }
 
 static void test_tagged_addr_abi_pmlen(int pmlen)

---
base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37
change-id: 20241204-fix_warnings_pointer_masking_tests-3860e4f35429
-- 
- Charlie