Re: Reinventing the Hurd server bootstrap

[Justus Winter]

Quoting Thomas Schmitt (2015-01-30 14:25:50)
> Hi,
> 
> Justus Winter wrote:
> > 3. Remaster using `grub-mkrescue --output=my-bootshell.iso /=master'.
> 
> The beauty of grub-mkrescue.

Yes, it's super nice :)
> > To start an translator on demand, the file system needs to support
> > storing a passive translator record somewhere.
> > [...]  I don't know if it would be possible to store it on a cd.
> 
> At what time would it have to be written ?
> If it's when the ISO is produced, then one just would have
> to negociate a suitable representation between xorriso and
> Hurd.

Production time.

> If it needs write capability at mount time, then it depends
> on the medium type. It would also break the model of a
> read-only filesystem.

It does not.

> > > I read https://www.debian.org/ports/hurd/hurd-doc-translator
> > Can you be more precise, e.g. cite the paragraph in question?
> 
> I mean the "underlying inode the translator is attached to",
> which gets introduced in #concept, demonstrated as mount point
> in #examples, and referred to in #actpas:
> "[...] the first time the passive translator is accessed,
>  it is automatically read out of the inode and an active
>  translator is started on top of it using the command line
>  that was stored in the inode."
> 
> Is this inode the mount point directory inode in the
> parent filesystem (e.g. in ext2) or is it the root directory
> of the ISO filesystem ?

The former. Though it doesn't need to be a directory node.  On the CD,
/run is a simple empty file.

> (Or does each inode of the ISO get attached a translator ?)

No.

> > ext2fs stores the
> > record in the operating system specific part of the ext2 ondisk
> > format.  That is undesireable for ext2.
> 
> Well, the System Area of ISO 9660 is playground of GRUB2 in
> this case. So it would be unwise to use it for translator
> info without coordination with GRUB2.
> 
> The System Use Area of the "." Directory Record in the
> extent of the ISO 9660 root directory would be a fine
> place for extra info. That's were SUSP and Rock Ridge info
> gets stored.
> One could define a new SUSP field for Hurd translators
> or use my AAIP extension, which i use to store Linux-ish
> xattr and ACL.
>   http://libburnia-project.org/wiki/AAIP
> In the latter case one would define one or more variable
> names in name space "isofs" or "system". (Depends on how
> close one wants to stay with Linux xattr habits.)
> 
> 
> Well, the overall question is: Is it worth an effort ?
> I.e. can the ISO stay read-only and does a passive translator
> provide advantages ?

I guess it could.  Then we wouldn't need to make /dev a tmpfs and
create it's content on demand.  Then again, doing so is easy enough
(with the bootshell).

:)
Justus