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Re: Reinventing the Hurd server bootstrap

From: Thomas Schmitt
Subject: Re: Reinventing the Hurd server bootstrap
Date: Fri, 30 Jan 2015 14:25:50 +0100


Justus Winter wrote:
> 3. Remaster using `grub-mkrescue --output=my-bootshell.iso /=master'.

The beauty of grub-mkrescue. 
More people should use it and increase its weight in GRUB2.

Even in the simple BIOS case, it already hides these expert
options of xorriso:

  --grub2-mbr ...disk.path...
  -c '/boot.catalog'
  -b '/boot/grub/i386-pc/eltorito.img'
  -boot-load-size 4

> 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
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.

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

> 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.
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 ?

Have a nice day :)


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