+ * To ensure good performance preferentially use the physical block size
+ * for proper alignment. The physical size is supposed to be the internal
+ * sector size used by the device. This is often 4096 byte for AF devices,
+ * while a smaller 512 byte logical size is supported for compatibility.
+ *
+ * Unfortunately, many drives still misreport their physical sector size.
+ * For devices which are known to lie you may need to manually set this
+ * at pool creation time with 'zpool create -o ashift=12 ...'.
+ *
+ * When the physical block size interface isn't available, we fall back to
+ * the logical block size interface and then the older hard sector size.
+ */
+#ifdef HAVE_BDEV_PHYSICAL_BLOCK_SIZE
+# define vdev_bdev_block_size(bdev) bdev_physical_block_size(bdev)
+#else
+# ifdef HAVE_BDEV_LOGICAL_BLOCK_SIZE
+# define vdev_bdev_block_size(bdev) bdev_logical_block_size(bdev)
+# else
+# define vdev_bdev_block_size(bdev) bdev_hardsect_size(bdev)
+# endif /* HAVE_BDEV_LOGICAL_BLOCK_SIZE */
+#endif /* HAVE_BDEV_PHYSICAL_BLOCK_SIZE */
+
+/*
+ * 2.6.37 API change
+ * The WRITE_FLUSH, WRITE_FUA, and WRITE_FLUSH_FUA flags have been
+ * introduced as a replacement for WRITE_BARRIER. This was done to
+ * allow richer semantics to be expressed to the block layer. It is
+ * the block layers responsibility to choose the correct way to
+ * implement these semantics.
+ *
+ * The existence of these flags implies that REQ_FLUSH an REQ_FUA are
+ * defined. Thus we can safely define VDEV_REQ_FLUSH and VDEV_REQ_FUA
+ * compatibility macros.