Re: [PATCH] wic: allow creation of partitions not in table

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

Hi,

On 05/02/2015 at 10:02:26 +0100, Maciej Borzecki wrote :
> On 02/05 00:03, Alexandre Belloni wrote:
> > For some architectures it is necessary to reserve space on disk without
> > it being present in the partition table.
> >
> > For example, u-boot on i.mx is placed at an offset of 1kB on the sdcard.
> > While it would be possible to create a partition at that offset and
> > place u-boot there, it would then be necessary to update the default
> > u-boot environment to use partition 2 on the mmc instead of partition
> > 1.
> 
> I'm wondering if reusing parition here is the right choice. How about
> making this a separate command, since the operation of putting some
> binary data at a particular location within the image sounds like
> something very specific to wic.
> 
> Could name it 'raw-copy', with options --source and --offset. The
> command would be applied after image assembly is complete. Offset could
> be expressed in bytes by default (plus k/M/G suffix). Source could
> either be a 'bootloader', that implies a default bootloader for this
> target, or a name of a file from $DEPLOY_DIR_IMAGE.
> 
> Assuming IMAGE_BOOTLOADER='u-boot.img' is set somewhere, the kickstart
> could look like:
> 
> part / --source rootfs --ondisk mmcblk --fstype=ext4 --label root --align 4 --start 1M
> raw-copy --source bootloader --offset 1kB
> 
> 
> If at some point we extend the bootloader command to include the name of
> bootloader file:
> 
> part / --source rootfs --ondisk mmcblk --fstype=ext4 --label root --align 4 --start 1M
> bootloader --name u-boot.img
> raw-copy --source bootloader --offset 1kB
> 
> What do you think?
> 

I though about that, I actually created a rawcopy plugin to dump file
into partitions.

The main issue with what you suggest is that you lose the whole
automatic offset calculations. What if the bootloader is larger than 1M
in your example? It will overwrite / You also lose the alignment
calculations unless you add them back in the new class.

Another issue is that you may want to copy multiple files at different
offsets. For example for am335x:
SPL at 128k, backup SPL at 256k, u-boot at 384k in a partition, u-boot
environment in a partition, rootfs.

This would give something like:
part SPL --source rawcopy --sourceparams="file=MLO" --ondisk mmcblk --no-table --align 128
part SPL.backup --source rawcopy --sourceparams="file=MLO" --ondisk mmcblk --no-table --align 128
part uboot --source rawcopy --sourceparams="file=u-boot.img" --ondisk mmcblk --align 128
part uboot.env --source rawcopy --sourceparams="file=u-boot.env" --ondisk mmcblk --align 128
part / --source rootfs --ondisk mmcblk --fstype=ext4 --label root --align 4

So, u-boot and its environment are in separate partitions and can be
updated easily from Linux.

Maybe instead of using part --no-table, we can name it nopart?

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com