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Re: [PATCH] Workaround for usb boot failure on some mainboards
From: |
Lennart Sorensen |
Subject: |
Re: [PATCH] Workaround for usb boot failure on some mainboards |
Date: |
Wed, 22 Sep 2010 12:14:46 -0400 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Wed, Sep 22, 2010 at 05:45:34PM +0200, Thomas Frauendorfer | Miray Software
wrote:
> On some boards, like the AsRock K7S41GX, Grub fails to boot from
> superfloppy fat32 formated usb sticks.
>
> The reason for the boot failure is that the bios of the mentioned
> board replaces byte 0x24 of the bpb with the value 0x00 when it's read
> through the bios function.
> In fat16 this byte contains the Disc unit number, so this causes no real
> harm there.
> In fat32 this byte is part of the sectors per FAT information, so by
> modifying this value the bios makes Grub unable to read the fat system.
>
> The attached workaround reads the backup bpb information on fat32
> filesystems and uses the sectors per fat information stored there.
>
> PS: I'm sorry if this mail is a duplicate, but I sent it before but I
> wasn't subscribed so it might have been blocked/dropped before
Wouldn't that be a bug in the BIOS? Don't go writing to a drive you
don't know what contains. It could be something other tahn fat16 after
all (what if it was a linux kernel with a bootheader on it and not a
filesystem at all?)
Sounds like the BIOS needs fixing badly. Nothing wrong with making
grub more robust against corrupt filesystems, but it doesn't actually
fix the bug in the BIOS.
--
Len Sorensen