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Splitted live-snapshot patches + some comments on snapshot internals

Marco Amadori <marco.amadori at gmail.com> writes:

> And now, for something completely RELATED:
> If I'll can I'll try to add a cpio.lzo target before the freeze; it is really 
> useful for slow systems since lzo is a very fast compression library, although 
> it is not a good candidate for replacing the default "cpio.gz" since the 
> latter is supported by busybox and klibc without external dependencies.
> The squashfs target is meant to be built in order to put it side the main 
> filesystem.squashfs on CDRW multisession open media, here an helper to reburn 
> just this snapshot would be great.
> The latter ext2 is meant to ease the creation of the "Cow" persistent media 
> instead of using tmpfs which is the original casper solution for persistence 
> from ubuntu. But this way has proven to be slow in practice, although is the 
> most "unplug power cord" friendly one.

Could you give a better explanation how this tmpfs solution used to
work? I didn't see it and would be interesting for a whole situation

> Both squashfs and ext2/3 target was only tested by me 2 years ago and worked 
> boot-wise. 
> Now cpio.gz is the only guaranteed target (fully tested by me on iso media  
> with the /etc/live-snapshot.list option).
> All other targets will fail until "/live/cow" will became visible again (this 
> bug is related with busybox/klibc recent mount changing, should be like the --
> move support btw).
> Squashfs support at boot was also added to support modules and hence the 
> concept in live-package (at that time) to build differents squashfs 
> incrementally, designed like it shoulded mounting at build time (now by live-
> helper) the chroot from the previous squashfs sets and a writable dir as the 
> cow, source of the new squashfs module block.
> But this could be a nice thing to have in lenny+1 since I just wrote a concept 
> for a old build system.
> A little brainstorming could help here to provide the most useful and flexible 
> "writeable" on a read-only media option to our users. There are many bugs and 
> missing features now, like deleting files (which needs .wh. whiteouts 
> internals of aufs/unionfs, or implementing custom mass delete at boot) or 
> copying only file which are really changed to save spaces.
> Any wishlist or ideas on snapshot/persistent topic here?

I've been using ext3 since ext2 corrupt too easily.

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