Mailinglist Archive: opensuse-arm (74 mails)

[Marcus Schäfer <ms@xxxxxxx>]

Hi,

> The start sector 2048 is the only thing that matters here to some tools.
> The sdcard standard requires all devices to have a single FAT32 partition
> starting at sector 8192, while some ancient (broken) versions of xloader
> required the first partition to start at sector 63, which is what old
> versions of fdisk used to do ms-dos compatibility.
>
> With the two partition layouts above, the first one is halfway sensible,
> because it actually fits the entire drive into the C/H/S layout with 122*
> 62*1017 blocks. The second one is not strictly valid in some tools because
> larger than 1024 cylinders should only be used together with 255 heads
> and 63 sectors on devices that have more than 8GB. For a 4GB card, the
> most reliable layout would be 128 heads and 32 sectors, because that lets
> you align the partitions to 4 MB while also allowing fdisk to detect
> the layout (which it cannot do otherwise). This trick does not work for 8GB
> cards though.
>
> What I think we do in Linaro is to always force a 255*63*xxxx layout
> when creating the partitions and aligning the partitions to 4MB but not
> a cylinder boundary.

I think what we do in kiwi is close to that. the geometry information
if not set by options is taken from what parted thinks about it.
As this happens through loop devices when the image is build the
faked geomtry used by the loop driver is always 255*63*xxxx.

The start sectors are aligned to be %8 clean and the to the cylinder
boundary. So far I did not had any trouble with that setup on 4G
SD cards (did not try on 8G cards though). For MLO loading I think
only the start address might matter... not sure

The start sector is set to 2048 because it's the default :)
It's possible to override that with

   kiwi --create ... --start-sector XX

at build time of the image

Regards,
Marcus
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