[yocto] How to partition a flash drive (was: Problem creating bootable flash)

[Chris Tapp]

Hi Paul,

On 1 Apr 2013, at 05:16, Paul D. DeRocco wrote:

>> From: Chris Tapp
>> 
>> This should end
>>   of=/dev/sdb
>> 
>> The hddimg file includes the partition info and both 
>> partitions, so you don't need any of the other steps.
> 
> Actually, the .hddimg is a single FAT16 volume, with no partition table,
> which contains files for creating a couple of different RAM disk images,
> which are part of the live-image mechanism.

Sorry, I was trying to do too many things late at night!

I confused myself with the image created using the 'install' boot option ;-)

> I am leaning toward using this live-image mechanism in my project
> permanently, because it almost eliminates the possibility of anything
> corrupting the OS in any persistent way. My application does have a small
> amount of persistent data, and I don't want to use the union or overlay file
> system as a way of adding persistence to the live image, because that sort
> of defeats the security of the live image. So I do indeed want to use a
> truly partitioned flash drive, and put my application data on a separate
> small partition.

Good choice, as unionfs isn't supported in the 3.0 kernel in Yocto.
I've used it before to give persistence using a read-only partition with some
scripts to make it writeable to allow configuration files (etc) to be updated
whilst still giving a decent level of protection.

> 
> What's going wrong is that the code in the MBR created by gparted (and I
> assume by parted) unconditionally uses drive number 0x80 (the first hard
> disk) when it tries to load the zeroth sector from the bootable partition.
> The BIOS, however, is treating this eUSB SSD as a removable drive, and
> calling it drive zero. So it's crashing at the point where the MBR code
> jumps to what is supposed to be the zeroth sector of the partition.
> 
> The code in the boot sector for the FAT16 volume uses whatever drive number
> is in the DL register on entry, and this works fine when booting directly
> from the BIOS into this code with no intervening MBR, so the solution is to
> modify the MBR boot code to do the same thing. This simply involves NOP-ing
> out the MOV DL, 80H instruction. Then, it should successfully boot a
> partitioned flash drive as though it were a hard disk.
> 
> -- 
> 
> Ciao,               Paul D. DeRocco
> Paul                mailto:pderocco at ix.netcom.com 
> 
> 

Chris Tapp

opensource at keylevel.com
www.keylevel.com