mtd2block should not expand sparse loopback files

[Johannes Niess]

Am Dienstag, 30. Mai 2006 13:03 schrieb Jörn Engel:
> On Mon, 29 May 2006 08:29:03 -0500, Josh Boyer wrote:
> > On 5/27/06, Johannes Niess <linux at johannes-niess.de> wrote:
> > >I guess that the "fill with 1's" flash strategy is taking its toll
> > > together with the "Clean" markers. Can I switch that off? Using
> > >"mkfs.jffs2 --no-cleanmarkers"  does not help, as does  --eraseblock=0.
> >
> > No you can't switch it off.  The filesystem will add them itself.
>
> For now.  I have a patch pending that removes the cleanmarker
> generation from jffs2.  Still needs some polishing, though.
>
> Basically, if the mtd can do implicit erase, like any RAM, disk or
> file-based device, there is no point in the cleanmarkers and jffs2
> doesn't write them.  There might be other cases where they can be
> omitted at well.

Hi Jörn,

That is great news. If your patch is still applicable to a released vanilla 
kernel  (or not requiring too many other patches) I'd volunteer as beta 
tester. I see potential of wide spread use in "compact" linux distributions. 
It makes it very easy to use a full scale distribution in reduced space.

I'm quite sure that you have seen the difference of mtd wanting 1's all over 
the place and a sparse file returning implicit 0's when reading in the holes. 
I've no idea whether this is relevant.

I had a quick look at the source if I could find the relevant parts and do 
some very nasty hacking. Given my very limited C programming skills ("C++ 
very easy", approx. 100 pages) and using Perl if I feel the need for some 
hobby programming, I had no chance.

Following up on Josh's hint to e2compr I had the feeling that 
"e2compr.infradead.org" would be an address to describe the current 
status :-)  But that stuff has patches to kernel 2.6.10 . I don't consider it 
being "alive" enough to be usefull.

Thank you again for developing mtd/jffs2!

Johannes
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