Re: 2.7 block ramblings (was Re: DMA for ide-scsi?)

Matt Domsch
2003-09-15T01:07:32Z

On Sun, Sep 14, 2003 at 05:26:54PM -0500, Alan Cox wrote:
> On Sad, 2003-09-13 at 17:11, Matt Domsch wrote:
> > system-unique disk signature to the boot disk (int13 device 80h)
> > "BOOT" or something - we've got 4 bytes available in the msdos label
> > for it
>
> int 13 is still available during the 16bit boot up phase of the kernel.
> It does strike me as playing with fire, but an alternative approach
> might work. Read the first 4K off the boot disk, stuff it somewhere
> temporary and then in 32bit compare it with the disk starts..

This is essentially what we are proposing, only instead of reading 4K,
read 1 sector and stash the 4-byte disk signature where we can get at
it later, and export it via edd.o for comparison later. This much is
easy, as the empty_zero_page has 512 bytes free for reading the sector
in setup.S, and 4 bytes we can use to stash the signature until
setup.c runs where we can copy it somewhere safe. Then export it via
edd.o through /proc (2.4) or /sys (2.6).

The thing that writes the signature to disk can be anything that can
issue int13 calls. Right now we do it in a FreeDOS app, but a special
loadlin/syslinux/isolinux used for OS installation may be simpler and
not require a FreeDOS environment be run ever.

-Matt

--
Matt Domsch
Sr. Software Engineer, Lead Engineer
Dell Linux Solutions www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com