Re: growisofs should have a method for padding
| From: Volker Kuhlmann <email@example.com>
| Completely forget all your this-year's redhat references. This problem
| existed at least with kernels 2.2 and 2.4, and is probably as old as
| Linux (see references to it for kernels 1.3 in older mkisofs/cdrecord
| source around the -pad option). In 2.2 it didn't usually show, in 2.4 it
| was difficult to prevent.
I've not experienced it until 2.6.
I often read raw CDs to compare what is on the CD with a .iso file.
My recollection is that before 2.6, there was code to better guess the
size of a volume. I was told this, so I don't know what form the code
| Adding zeros to your image files doesn't change your checksums if you
| compute them properly, ie on the ISO image only. I've got scripts for
| all the above in my scriptutils package. It does damage any signatures
| though, there you ought to use padding with mkisofs.
I think that K3B does an md5sum of the disk, taking its idea of file
length from the drive. This just does not work.
The md5sum command does not take a length argument, so you need to use
dd piped to md5sum, where the dd does the truncating. My (long ago)
experience with this pipeline was quite unpleasant: I think that it busted
the disk cache (as in: the cache was ineffective, not buggy).
| The default 20k padding was nowehre near enough on some DVD ISOs on 2.4.
Default for what? -pad? DVD mastering?
| I agree that it would be useful in growisofs. However a suitable wrapper
| script should fix it too.
| > /usr/bin/growisofs: no mkisofs options are permitted with =, aborting...
| Well, if that "=" is with -Z, then growisofs is told to burn an image,
| where you're already past mkisofs and therefore barfing on mkisofs
| options is a good thing as it may save you a coaster (and makes no sense
mkisofs, a mastering program, implements -pad/-padsize. But I'm
proposing a second meaning: post-mastering padding. Perhaps the
option name should be changed, but I think that the idea is useful.