ceph: fix file offset wrapping at 4GB on 32-bit archs

Cast the value before shifting so that we don't run out of bits with a
32-bit unsigned long.  This fixes wrapping of high file offsets into the
low 4GB of a file on disk, and the subsequent data corruption for large
files.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/addr.c

@@ -766,7 +766,8 @@ static int ceph_writepages_start(struct address_space *mapping,
 			/* ok */
 			if (locked_pages == 0) {
 				/* prepare async write request */
-				offset = page->index << PAGE_CACHE_SHIFT;
+				offset = (unsigned long long)page->index
+					<< PAGE_CACHE_SHIFT;
 				len = wsize;
 				req = ceph_osdc_new_request(&client->osdc,
 					    &ci->i_layout,