Re: Interest in DOC and YAFFS? --> YAFFS bootloading

[Marc Singer <elf@buici.com>]

On Tue, Sep 24, 2002 at 09:59:03AM -0700, Russ Dill wrote:
> On Tue, 2002-09-24 at 09:53, Marc Singer wrote:
> > On Tue, Sep 24, 2002 at 12:53:36AM -0700, Russ Dill wrote:
> > > 
> > > > Some people think that writing a new kernel would be easy.  %^)
> > > > 
> > > > The trouble is coming up with a convenient method.  LILO stores a list
> > > > of blocks.  GRUB reads filesystems.  GRUB is better in the long run,
> > > > but harder to implement.
> > > 
> > > I've written a cramfs reader for grub, to use on the DOC, and grub works
> > > great on a DOC. Although the grub code is a bit ugly, and there are a
> > > few gotchas, writing a module is pretty straight forward. That being
> > > said, writing a module to load files of a journaled fs (jffs2), is a bit
> > > more time consuming, but as I understand yaffs is greatly optimized
> > > towards NAND (as apposed to NOR) flash layout and lends itself to easy
> > > reading (same sized blocks, no compression iirc).
> > > 
> > > If I were you, I'd use grub.
> > 
> > That's what I'd expect.
> > 
> > A question, though.  I've been doing compression tests with cramfs.
> > I'm finding that gzip -9 of an ext2 filesystem produces smaller images
> > than mkcramfs.  Have you ever compared the two?
> 
> cramfs is meant to be lean, fast, and low on ram consumption, if you
> compress the whole thing at once, you have to load the whole thing into
> ram to read any of it, so cramfs compresses PAGE_CACHE (4096) sized
> pages at a time

That's what isn't clear.  I made two filesystems with the same
contents.  One cramfs and the other ext2.  The ext2 filesystem
compressed was smaller than the cramfs.  My understanding is that both
must be uncompressed into a ramfs to be used.  If this is correct,
then the only comparable consideration is the size of the compressed
data.