[Gllug] Undelete...?

Nix nix at esperi.org.uk
Tue Feb 10 01:33:47 UTC 2004

On Sat, 7 Feb 2004, Ian Norton mused:
> On Thu, Feb 05, 2004 at 07:59:00PM +0000, Richard Huxton wrote:
>> Note that I wasn't suggesting these files should be kept permanently, just 
>> relink them to another (semi-special) location while the free-space they 
>> represent isn't needed. If the disk is low on space, your files won't survive 
>> long - if it isn't low on space, why not keep them?
> This sounds like to me just how fragmentation happens :-)

No, there's a good idea there: link the files into a semi-hidden area of the
disk and track their original location (perhaps by encoding it in the new
filename a-la Emacs save files).

Then add a new kind of file: `weak regular files'. Revise the FS block
allocator to consider blocks allocated by weak regular files just like
free space, except that before allocating blocks in that area,
free up the weak regular file to which they are allocated.

The downside is that the last step requires a disk block -> inode
mapping, which filesystems like ffs, ext[23] and so on simply don't
maintain. reiserfs does, though, and this mapping is useful for
things like transparent background compression / CoW as well; so
it's a good potential design for future filesystems.

(Like the one I'm slowly designing. Thanks for the idea! :) )

`note to the crown prosecution service: Machine guns dont have a
 'stun' setting.' --- mjw
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