[Someone wrote:]
> > I once used a multisession CD-ROM (don't recall the brand) whose authoring
> > software and device driver allowed for incremental backups. The driver
> > would present the multisession CD-ROM as one filesystem where you only saw
> > the most recent version of a given file. It was pretty slick.
> That would be a lot like having a CD-ROM filesystem that acted like an
> inherited filesystem. Thus, you could do a backup on track 1 and then
> incrementally write only the files that had changed to subsequent tracks.
> When you mounted the CD-ROM you'd see only the latest versions of the
> files that were backed up. I remember their being an IFS in the kernel
> sometime ago, but it disappeared (I think (?)).
I don't know about isofs internals, but I thought you could do this without
any special support on the reader? When laying down the new session I believe
directory entries can be written which refer to files in previous sessions,
if the file is unchanged. If it is changed, the file is written to the new
session and the new directory entry points to that. If it doesn't exist, no
directory entry is written. Or are the directories from all the sessions
overlaid, in which case whiteouts would be needed?
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