@@ 1,5 1,5 @@
;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2014, 2015, 2016, 2017 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2016, 2017 David Craven <david@craven.ch>
;;;
;;; This file is part of GNU Guix.
@@ 72,22 72,33 @@
"Bind-mount SOURCE at TARGET."
(mount source target "" MS_BIND))
+(define (seek* fd/port offset whence)
+ "Like 'seek' but return -1 instead of throwing to 'system-error' upon
+EINVAL. This makes it easier to catch cases like OFFSET being too large for
+FD/PORT."
+ (catch 'system-error
+ (lambda ()
+ (seek fd/port offset whence))
+ (lambda args
+ (if (= EINVAL (system-error-errno args))
+ -1
+ (apply throw args)))))
+
(define (read-superblock device offset size magic?)
"Read a superblock of SIZE from OFFSET and DEVICE. Return the raw
superblock on success, and #f if no valid superblock was found. MAGIC?
takes a bytevector and returns #t when it's a valid superblock."
(call-with-input-file device
(lambda (port)
- (seek port offset SEEK_SET)
-
- (let ((block (make-bytevector size)))
- (match (get-bytevector-n! port block 0 (bytevector-length block))
- ((? eof-object?)
- #f)
- ((? number? len)
- (and (= len (bytevector-length block))
- (and (magic? block)
- block))))))))
+ (and (= offset (seek* port offset SEEK_SET))
+ (let ((block (make-bytevector size)))
+ (match (get-bytevector-n! port block 0 (bytevector-length block))
+ ((? eof-object?)
+ #f)
+ ((? number? len)
+ (and (= len (bytevector-length block))
+ (and (magic? block)
+ block)))))))))
(define (sub-bytevector bv start size)
"Return a copy of the SIZE bytes of BV starting from offset START."