. readall: use lseek64() to read more than 4GB of a device

. vfs: 64-bit offset support for character device i/o
   (also remove unused dev_bio function)
 . memory: /dev/null and /dev/zero are infinitely large, don't stop
   reading/writing at 4GB

commands/simple/readall.c

@@ -124,8 +124,8 @@ char *argv[];
   /* Read the entire file. Try it in large chunks, but if an error
    * occurs, go to single reads for a while. */
   while (1) {
-	if(lseek(fd, BLOCK_SIZE * b, SEEK_SET) < 0) {
-		perror("lseek");
+	if(lseek64(fd, mul64u(BLOCK_SIZE, b), SEEK_SET, NULL) < 0) {
+		perror("lseek64");
 		return 1;
 	}
 	s = read(fd, a, BLOCK_SIZE * chunk);