[LTP] [PATCH v4 6/6] syscalls/readahead02: test readahead using posix_fadvise()

[Amir Goldstein <amir73il@gmail.com>]

The call to posix_fadvise(POSIX_FADV_WILLNEED) should have the same
effect as the call to readahead() syscall.

Repeat the test cases for local file and overlayfs file with
posix_fadvise().

The new test case is a regression test for kernel commit b833a3660394
("ovl: add ovl_fadvise()") which fixes a regression of fadvise() on
an overlay file that was introduced by kernel commit 5b910bd615ba
("ovl: fix GPF in swapfile_activate of file from overlayfs over xfs").

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 .../kernel/syscalls/readahead/readahead02.c   | 41 +++++++++++++++----
 1 file changed, 34 insertions(+), 7 deletions(-)

diff --git a/testcases/kernel/syscalls/readahead/readahead02.c b/testcases/kernel/syscalls/readahead/readahead02.c
index 73c8a6ce6..44475487e 100644
--- a/testcases/kernel/syscalls/readahead/readahead02.c
+++ b/testcases/kernel/syscalls/readahead/readahead02.c
@@ -54,12 +54,30 @@ static struct tst_option options[] = {
 static struct tcase {
 	const char *tname;
 	int use_overlay;
+	int use_fadvise;
 } tcases[] = {
-	{ "readahead on file", 0 },
-	{ "readahead on overlayfs file", 1 },
+	{ "readahead on file", 0, 0 },
+	{ "readahead on overlayfs file", 1, 0 },
+	{ "POSIX_FADV_WILLNEED on file", 0, 1 },
+	{ "POSIX_FADV_WILLNEED on overlayfs file", 1, 1 },
 };
 
+static int fadvise_willneed(int fd, off_t offset, size_t len)
+{
+	/* Should have the same effect as readahead() syscall */
+	return posix_fadvise(fd, offset, len, POSIX_FADV_WILLNEED);
+}
+
+static int libc_readahead(int fd, off_t offset, size_t len)
+{
+	return readahead(fd, offset, len);
+}
+
+typedef int (*readahead_func_t)(int, off_t, size_t);
+static readahead_func_t readahead_func = libc_readahead;
+
 static int readahead_supported = 1;
+static int fadvise_supported = 1;
 
 static int has_file(const char *fname, int required)
 {
@@ -135,7 +153,6 @@ static void create_testfile(int use_overlay)
 	free(tmp);
 }
 
-
 /* read_testfile - mmap testfile and read every page.
  * This functions measures how many I/O and time it takes to fully
  * read contents of test file.
@@ -163,7 +180,7 @@ static void read_testfile(int do_readahead, const char *fname, size_t fsize,
 	if (do_readahead) {
 		cached_start = get_cached_size();
 		do {
-			TEST(readahead(fd, offset, fsize - offset));
+			TEST(readahead_func(fd, offset, fsize - offset));
 			if (TST_RET != 0) {
 				SAFE_CLOSE(fd);
 				return;
@@ -241,6 +258,9 @@ static void test_readahead(unsigned int n)
 
 	create_testfile(tc->use_overlay);
 
+	/* Use either readahead() syscall or POSIX_FADV_WILLNEED */
+	readahead_func = tc->use_fadvise ? fadvise_willneed : libc_readahead;
+
 	/* find out how much can cache hold if we read whole file */
 	read_testfile(0, testfile, testfile_size, &read_bytes, &usec, &cached);
 	cached_high = get_cached_size();
@@ -263,13 +283,20 @@ static void test_readahead(unsigned int n)
 	read_testfile(1, testfile, testfile_size, &read_bytes_ra,
 		      &usec_ra, &cached_ra);
 	if (TST_RET != 0) {
-		if (TST_ERR == EINVAL &&
-		    (!tc->use_overlay || !readahead_supported)) {
+		/* posix_fadvise returns error number (not in errno) */
+		if (tc->use_fadvise && (TST_ERR = TST_RET) == EINVAL &&
+		    (!tc->use_overlay || !fadvise_supported)) {
+			fadvise_supported = 0;
+			tst_res(TCONF, "fadvise not supported on %s",
+				tst_device->fs_type);
+		} else if (TST_ERR == EINVAL &&
+			   (!tc->use_overlay || !readahead_supported)) {
 			readahead_supported = 0;
 			tst_res(TCONF, "readahead not supported on %s",
 				tst_device->fs_type);
 		} else {
-			tst_res(TFAIL | TTERRNO, "readahead failed on %s",
+			tst_res(TFAIL | TTERRNO, "%s failed on %s",
+				tc->use_fadvise ? "fadvise" : "readahead",
 				tc->use_overlay ? "overlayfs" :
 				tst_device->fs_type);
 		}
-- 
2.17.1