Re: ext4 features

[Bill Davidsen]

Peter Zijlstra wrote:
> On Tue, 2006-07-04 at 11:22 +0200, Petr Tesarik wrote:
> > On Mon, 2006-07-03 at 23:25 +0200, Diego Calleja wrote:
> > > El Mon, 03 Jul 2006 15:46:55 -0600,
> > > "Jeff V. Merkey" <jmerkey@xxxxxxxxxxxxxxxxxxxxx> escribiÃ:
> > >
> > > > Add a salvagable file system to ext4, i.e. when a file is deleted, you 
> > > > just rename it and move it to a directory called DELETED.SAV and recycle 
> > > > the files as people allocate new ones.  Easy to do (internal "mv" of 
> > >
> > > Easily doable in userspace, why bother with kernel programming
> > Yes and no. A simple mv is better done in userspace, but what I'd
> > _really_ appreciate would be a true kernel salvage (similar to the way
> > NetWare does things). That means marking the file as deleted in the
> > directory, marking its blocks as deleted but avoiding the use of those
> > blocks. The kernel would then prefer allocating new blocks from
> > elsewhere but once the filesystem runs out of space, it would start
> > allocating from the deleted files area and marking the blocks as well as
> > the corresponding files purged.
> >
> > Salvaging files would be done with a separate tool. Of course, if you
> > delete more files with the same name in the same directory, you'd need
> > to tell that tool which one of them you want to salvage. Yes, I really
> > mean you'd have more than one deleted file with the same name in the
> > directory.
> >
> > Anyway, I doubt we want such feature for ext4, because to make things
> > efficient, you'd need to provide some kind of pointer from the deleted
> > (but not yet purged) blocks to the corresponding file. Hard links are
> > also problematic and there is a whole lot of other troubles I haven't
> > even thought of.
>
> Wouldn't such a scheme interfere with the block allocator algorithms,
> and hence increase the risk of fragmentation? Schemes like this realy
> put my hairs on end,
>
>   1) if you don't want to lose your data, make backups; 
>   2) if I mean to delete a file, I want it gone proper. Silently keeping
>      it about is not unix like;
>   3) don't aid third parties in recovering your removed data. If I want
>      them to have it I'll give it to them.
>
> Peter
If you wanted to add a feature which would overwrite the file when 
removed or truncated I'd be happy. Yes I know about attributes and dban, 
and I have a version of rm which does that if people use it, but would 
be nice to have it on the whole filesystem. It's not proof against a 
TLA, but nice for casual snooping.

--
Bill Davidsen <davidsen@xxxxxxx>
  Obscure bug of 2004: BASH BUFFER OVERFLOW - if bash is being run by a
normal user and is setuid root, with the "vi" line edit mode selected,
and the character set is "big5," an off-by-one errors occurs during
wildcard (glob) expansion.

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