Re: Ext2fs for pupa

[Yoshinori Okuji]

Hi Marco,

 --- Marco Gerards <address@hidden> wrote:
> I was wondering if it is interested to add ext3 support, so it is
> possible to boot from a broken ext3 fs.  Does it happen often that
> GRUB can't boot from a broken ext3 partition?

I'm really interested. Indeed, I was trying to implement ext3 support when I
was rewriting ext2 support for GRUB.

But, for your question, I must say that it is rare. Probably it is because GRUB
only accesses few blocks in a filesystem (i.e. /boot/grub/* and kernels in the
root directory or the boot directory). Journaling support is still useful,
however.
 
> So, does it make sense to implement this?  Do you have some other
> suggestions?

One caution is that you need to expect that memory would exhaust if you load
journals in memory. As GRUB/PUPA should run in 4MB and the journal size could
be at most 400MB, it is impossible to store all of them in memory. But if you
fetch each journal every time from a disk, it would be too slow.

Thus I think you will have to implement a cache mechanism such as LRU. This is
too difficult in GRUB, but this shouldn't be difficult in PUPA, because you
have basic memory management functions. You might be able to get an idea from
the reiserfs code in GRUB, but I'm sure that you will do a better solution with
PUPA. :)

Thanks,
Okuji