Re: grub-probe fails to find PC partition due to Apple disklabel

[Pavel Roskin]

Quoting Chris Knadle <address@hidden>:

>    I'm trying to figure out how to get grub to check the first   
> sector.  Mainly
> I'm asking for hints.  I think it involves running a new instance of
> grub_disk_read for the first sector (sector 0 of the partition) within the
> apple_partition_map_iterate function -- something like:
>
>  grub_disk_read(&raw, 0, 0, sizeof (struct grub_apple_part), (char *)&apart))

I'm not sure grub_apple_part would describe the first sector  
correctly.  Besides, you only need two bytes.  Why reuse "apart"?  You  
can use a 16-bit variable and read those two bytes there.

>    But then I want to check the first block against 0x4552, and
> apart.first_phys_block is 32-bits.

Why first_phys_block?  The first field is 16 bit wide and is called "magic".

> Since I want the first (high) 16 bits, I
> think I need to make the comparison in a way such as:
>
>    if ((apart.first_phys_block & 0xFFFF0000) == (0x4552 << 16))

That won't work on little endian systems, including ordinary PC.  You  
are assuming big endian byte order here.  Instead, the data from the  
disk should be converted to CPU-endian from whatever it is and  
compared to the magic value.

--
Regards,
Pavel Roskin