[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: growisofs should have a method for padding

| From: Volker Kuhlmann <hidden@paradise.net.nz>

| 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
| either).

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.

Reply to: