Syslinux - Jan 2014 - [PATCH] Proposal for a pacifier option with mkdiskimage

Hi,

i too played with mkdiskimage in order to get more Linux examples.

When i applied it to a real 2 GB stick with write speed 4 MB/s
i had enough time to add some pacifier code to the big zeroizer
loop. (-s does not prevent zeroizing on block device. Probably
because truncate() fails.)

My pacifier is combined with what Perl advised me when i tried
"fsync(OUTPUT);". Of course this slows down operation on
regular files substantially.
But otherwise there is on USB sticks a super fast pacifier at
the start and a long time of no visible progress at the end.

So the pacifier is disabled unless option -S is given.
Other than regular files, USB sticks get really synced at
the end of the program in exit(0). At least on my Linux 2.6.
So syncing them intermediately does not impose an overall
time penalty. (And they don't rattle like synced hard disks.)

Would this patch have a chance to be accepted ?
It is based on
 
http://git.kernel.org/cgit/boot/syslinux/syslinux.git/tree/utils/mkdiskimage.in?id=syslinux-6.03-pre1

-------------------------------------------------------------------
--- mkdiskimage.in    2014-01-23 12:23:34.000000000 +0100
+++ mkdiskimage_ts.in 2014-01-23 17:00:59.000000000 +0100
@@ -145,6 +145,7 @@ if ( $file eq '' || $c < 1 || $h < 1 || 
     print STDERR "    -4    use partition entry 4 (standard for
zipdisks)\n";
     print STDERR "    -i    specify the MBR ID\n";
     print STDERR "    -s    output a sparse file (don't allocate all
blocks)\n";
+    print STDERR "    -S    sync after each zeroized cylinder and show
count\n";
     exit 1;
 }
 
@@ -221,12 +222,23 @@ $tracks    = $c*$h;
 unless ($opt{'s'} && truncate(OUTPUT, $totalsize)) {
     $track = "\0" x (512*$s);
 
+    $show_pacifier = $opt{'S'};
+
     # Print fractional track
     print OUTPUT "\0" x (512 * ($s-1));
 
     for ( $i = 1 ; $i < $tracks ; $i++ ) {
+	if ( $show_pacifier && ( $i - 1 ) % $h == 0) {
+	    $cyl_to_write = ( $i - 1 ) / $h + 1;
+	    IO::Handle::sync(OUTPUT);
+	    print STDERR " zeroizing cylinder $cyl_to_write of $c\r";
+	}
 	print OUTPUT $track;
     }
+    if ( $show_pacifier ) {
+	IO::Handle::sync(OUTPUT);
+	print STDERR " $totalsize blocks zeroized.              \n";
+    }
 }
 
 # Print mtools temp file
--------------------------------------------------------------------

Disclaimer: I am not really a Perl programmer.

Double disclaimer: I have never prepared a git-ish patch but i would
                   obey instructions.


Have a nice day :)

Thomas

> It is based on
>  
http://git.kernel.org/cgit/boot/syslinux/syslinux.git/tree/utils/mkdiskimage.in?id=syslinux-6.03-pre1
Just a thought (FWIW).
Perhaps it could be useful to base it on the syslinux4-xx branch:

http://git.zytor.com/?p=syslinux/syslinux.git;a=tree;h=refs/heads/sysl
inux-4.xx;hb=syslinux-4.xx

http://git.zytor.com/?p=syslinux/syslinux.git;a=blob_plain;f=utils/mkd
iskimage.in;hb=syslinux-4.xx

http://git.zytor.com/?p=syslinux/syslinux.git;a=blob_plain;f=utils/mem
diskfind.c;hb=syslinux-4.xx

http://git.zytor.com/?p=syslinux/syslinux.git;a=blob;f=utils/mkdiskima
ge.in;h=533193a1c301d249a89a63fa81dbf081df0bca6c;hb=syslinux-4.xx

http://git.zytor.com/?p=syslinux/syslinux.git;a=blob;f=utils/memdiskfi
nd.c;h=815f8bc1c1b1aad6cdb52ef1dd400983fe2a8ee0;hb=syslinux-4.xx

Regards,
Ady.

Hi,

Ady wrote:
> Perhaps it could be useful to base it on the syslinux4-xx branch:
>
http://git.zytor.com/?p=syslinux/syslinux.git;a=blob_plain;f=utils/mkdiskimage.in;hb=syslinux-4.xx
The mkdiskimage.in in git.kernel.org/.../syslinux-6.03-pre1
is identical with this.

I came to git.kernel.org via
 
http://www.syslinux.org/wiki/index.php/Development#Browse_the_SYSLINUX_source_code
Is 4.xx the recommended branch for changes ?
(Is there an automated migration path to higher versions ?)


Have a nice day :)

Thomas

On 01/23/2014 08:47 AM, Thomas Schmitt wrote:
> Hi,
> 
> i too played with mkdiskimage in order to get more Linux examples.
> 
> When i applied it to a real 2 GB stick with write speed 4 MB/s
> i had enough time to add some pacifier code to the big zeroizer
> loop. (-s does not prevent zeroizing on block device. Probably
> because truncate() fails.)
> 
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.

	-hpa

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