src/seek_sanity_test: discover allocation size

Try to discover the allocation size.  For NFS, the st_blksize is
optimized for the network, and will usually be much larger than the
allocation size of the exported filesystem, which may trigger
preallocation strategies in the exported filesystem causing the seek
tests here to fail.

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

1 files changed, 34 insertions, 7 deletions

diff --git a/src/seek_sanity_test.c b/src/seek_sanity_test.c
index 18262c2b04..a6dd48cc25 100644
--- a/src/seek_sanity_test.c
+++ b/src/seek_sanity_test.c
@@ -700,8 +700,8 @@ static int run_test(struct testrec *tr)
 
 static int test_basic_support(void)
 {
-	int ret = -1, fd;
-	off_t pos;
+	int ret = -1, fd, shift;
+	off_t pos = 0, offset = 1;
 	char *buf = NULL;
 	int bufsz, filsz;
 
@@ -715,6 +715,35 @@ static int test_basic_support(void)
 	if (ret)
 		goto out;
 
+	/* try to discover the actual alloc size */
+	while (pos == 0 && offset < alloc_size) {
+		offset <<= 1;
+		ftruncate(fd, 0);
+		pwrite(fd, "a", 1, offset);
+		pos = lseek(fd, 0, SEEK_DATA);
+	}
+
+	/* bisect */
+	shift = offset >> 2;
+	while (shift && offset < alloc_size) {
+		ftruncate(fd, 0);
+		pwrite(fd, "a", 1, offset);
+		pos = lseek(fd, 0, SEEK_DATA);
+		offset += pos ? -shift : shift;
+		shift >>= 1;
+	}
+	if (!shift)
+		offset += pos ? 0 : 1;
+	alloc_size = offset;
+
+	if (pos == -1) {
+		fprintf(stderr, "Kernel does not support llseek(2) extension "
+			"SEEK_DATA. Aborting.\n");
+		ret = -1;
+		goto out;
+	}
+
+	ftruncate(fd, 0);
 	bufsz = alloc_size * 2;
 	filsz = bufsz * 2;
 
@@ -734,12 +763,10 @@ static int test_basic_support(void)
 		goto out;
 
 	/* Is SEEK_DATA and SEEK_HOLE supported in the kernel? */
-	pos = lseek(fd, 0, SEEK_DATA);
-	if (pos != -1)
-		pos = lseek(fd, 0, SEEK_HOLE);
+	pos = lseek(fd, 0, SEEK_HOLE);
 	if (pos == -1) {
-		fprintf(stderr, "Kernel does not support llseek(2) extensions "
-			"SEEK_HOLE and/or SEEK_DATA. Aborting.\n");
+		fprintf(stderr, "Kernel does not support llseek(2) extension "
+			"SEEK_HOLE. Aborting.\n");
 		ret = -1;
 		goto out;
 	}