aiodio_sparse2: fix up alignment for 4k logical block sized devices

When running xfstests on a 4k logical sector device, I ran into a test
failure in test 198.  The errors were all due to trying to do 512 byte
aligned I/O on a 4k logical sector device.  The attached patch tries to
auto-detect the proper block size if no alignment is specified.  If it
fails for one reason or another, it defaults to 4k alignment.  This
seems to work fine in my test rig.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

src/aio-dio-regress/aiodio_sparse2.c

@@ -19,6 +19,8 @@
 #include <limits.h>
 #include <sys/mman.h>
 #include <sys/wait.h>
+#include <sys/ioctl.h>
+#include <sys/mount.h>
 
 #include <libaio.h>
 
@@ -274,6 +276,23 @@ void dirty_freeblocks(char *filename, int size)
 	unlink(filename2);
 }
 
+static long get_logical_block_size(char *filename)
+{
+	int fd;
+	int ret;
+	int logical_block_size;
+
+	fd = open(filename, O_RDONLY);
+	if (fd < 0)
+		return 4096;
+
+	ret = ioctl(fd, BLKSSZGET, &logical_block_size);
+	close(fd);
+	if (ret < 0)
+		return 4096;
+	return logical_block_size;
+}
+
 void usage()
 {
 	fprintf(stderr, "usage: dio_sparse [-n step] [-s filesize]"
@@ -314,7 +333,7 @@ long long scale_by_kmg(long long value, char scale)
 int main(int argc, char **argv)
 {
 	char filename[PATH_MAX];
-	long alignment = 512;
+	long alignment = 0;
 	int readsize = 65536;
 	int writesize = 65536;
 	int startoffset = 0;
@@ -376,6 +395,8 @@ int main(int argc, char **argv)
 
 	strncpy(filename, argv[argc-1], PATH_MAX);
 
+	if (alignment == 0)
+		alignment = get_logical_block_size(filename);
 	/*
 	 * Create some dirty free blocks by allocating, writing, syncing,
 	 * and then unlinking and freeing.