Re: Scripting - write to HD support?

[Hollis Blanchard <hollis@penguinppc.org>]

On Fri, 2006-10-06 at 20:43 +0200, Marco Gerards wrote:
> "Markus Laire" <malaire@gmail.com> writes:
> 
> > On 10/5/06, Marco Gerards <mgerards@xs4all.nl> wrote:
> >> I'm looking forwards to your ideas, questions, suggestions, criticism
> >> and bug reports. :-)
> >
> > Will there be any support for writing data to HD? Even a simple
> > support for writing some data to HD would allow quite a lot of ideas
> > to be implemented in grub which would be impossible with read-only
> > access.

I agree this would be a great feature.

> The disk support in GRUB 2 supports writing to disk.  However, it is
> not used.
> 
> > Full support for writing to filesystems is likely far too much to ask.
> 
> Right.
> 
> > But what about a possibility to create a certain file in advance (e.g.
> > /boot/grub/mydata filled with e.g. 1MB of zeroes) and then an ability
> > to write to that file without changing the size of the file.
> 
> Writing zero's reliable.  For example, filesystem implementations
> might change this into a sparse file.  Another problem could be
> reiserfs, which stores metadata and data in the same sectors, IIRC.
> 
> So instead of using zero's, we could of course use ones.  For reiserfs
> we would have to look how big the file has to be to make sure metadata
> won't share this sector.
> 
> But still, it is something we have to be extremely careful with.  And
> a more important question is: Why do you want this, do you have
> specific uses for such feature in mind?  I can think of things like
> fallback, etc.

Yeah, we should focus on enabling some specific features.

> > Alternative idea would be to create a partition (without any
> > filesystem) specifically for saving some data from grub, and then grub
> > would just give a read/write access to that partition as a single
> > block of data.
> 
> I don't like this, it will make it hard or impossible to install GRUB
> on certain systems.

I like this; it's nice and simple. It's also similar to the situation
with Open Firmware and NVRAM. This approach could extend to NVRAM on
other systems as well...

Systems without a free partition just wouldn't be able to take advantage
of the feature.

-Hollis