[syslinux] [PATCH] Proposal for a pacifier option with mkdiskimage

[Thomas Schmitt]

Hi,

me:
> > [mkdiskimage] -s does not prevent zeroizing on block device. Probably
> > because truncate() fails.

hpa:
> Yes, we should probably fix that.  The tool was originally designed for
> images, not for hardware devices, and it doesn't make much sense to zero
> the whole hardware device like that.

Maybe for privacy reasons ?
But indeed: -s should skip zeroizing, regardless of truncate.

Additionally the argument of truncate is currently wrong by a
factor of 512:
  $ mkdiskimage_orig.in -s image.img 250 64 32
  $ ls -l image.img
  -rw-r--r-- 1 xyz xyz  512000 2014-01-28 08:33 image.img


How about this ?
Tested with USB stick and image file, with and without -s:
-------------------------------------------------------------------------
--- mkdiskimage_orig.in    2014-01-23 12:23:34.000000000 +0100
+++ mkdiskimage_with_lower_s.in    2014-01-28 08:25:02.000000000 +0100
@@ -217,8 +217,11 @@ print OUTPUT "\x55\xaa";
 $totalsize = $c*$h*$s;
 $tracks    = $c*$h;
 
-# If -s is given, try to simply use truncate...
-unless ($opt{'s'} && truncate(OUTPUT, $totalsize)) {
+# If -s is given, simply use truncate. Do not care for success. Failure is
+# normal with Linux block devices.
+if ($opt{'s'}) {
+    truncate(OUTPUT, $totalsize * 512);
+} else {
     $track = "\0" x (512*$s);
 
     # Print fractional track
-------------------------------------------------------------------------

One could test for regular file and issue a warning message.
But i assume that access problems would already show up when
the MBR is written.

Is there the risk of 32 bit rollover with "$totalsize * 512"
with Perl on 32 bit machines ?
(My amd64 can handle -M 6000 255 63.)


After my wiki activities i still wonder:

Is mkdiskimage supposed to work on NT/2K/XP/DOS systems ?
Perl plus MS goes quite beyond my horizon.


Have a nice day :)

Thomas