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
understanding.
> Both squashfs and ext2/3 target was only tested by me 2 years ago and worked
> boot-wise.
>
> BEWARE:
>
> 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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