#define READ 0
#define WRITE 1
#define READA 2 /* read-ahead - don't block if no resources */
+#define SWRITE 3 /* for ll_rw_block() - wait for buffer lock */
#define SPECIAL 4 /* For non-blockdevice requests in request queue */
#define READ_SYNC (READ | (1 << BIO_RW_SYNC))
#define WRITE_SYNC (WRITE | (1 << BIO_RW_SYNC))