Hello!
I cannot promise I'll do the coding myself, but I've been thinking of
a safe approach to savedefault implementation, and I'd like to share
some of my thoughts.
GRUB should support only one kind of writing to the disk, namely
writing to one sector at a specified offset. Even that is not
trivial, as we should try to support BIOS, openfirmware and ATA. And
maybe we should try to support RAID at some point.
There should be a utility capable of creating a "blessed sector" where
GRUB would be allowed to write. Choosing the location is up to that
utility and the user running it. It could be a bootloader area of a
partition, a sector on the first track of the hard drive or a file on
the filesystem.
The utility must ensure that GRUB can write to that sector safely at
the boot time. In particular, it should be indeed aligned at the
sector boundary, it should not be compressed or fragmented. If it's
on RAID, the bootloader should know what to do. Only GRUB and the
utility should ever write to that sector. Using any other tools
should be discouraged.
What could be in the "blessed sector":
version of the utility that created it
minimal version of GRUB allowed to write
sector size
sector number on the drive
data length
modification time?
counter, which is incremented on write?
drives and sectors to write copies to?
settings, perhaps stored as 0-terminated strings in the format key=value
GRUB should read the sector first, perhaps using the filesystem. It
should check that its version is at least the required one. Then it
should re-read the sector by the sector number. The data should be
exactly the same. That should allow writing by the sector number.
The command for writing should save variables from the environment.
Likewise, reading from the file should copy variables to the
environment.
--
Regards,
Pavel Roskin
_______________________________________________
Grub-devel mailing list
Grub-devel@gnu.org
http://lists.gnu.org/mailman/listinfo/grub-devel
