Re: [PATCH] expand-on-first-boot: Allow expanding extended MBR partitions

[Jan Kiszka <jan.kiszka@siemens.com>]

On 10.06.20 10:02, Harald Seiler wrote:
> Extended partitions cannot be resized like primary partitions because
> both the last logical partition and the EBR primary partition containing
> it need to be expanded.
> 
> To do this, add a second SED directive for removing the parition size of
> the EBR partition.  This part is detected by having either type `f` (Win
> 95 Ext') or `5` (Extended).
> 
> Signed-off-by: Harald Seiler <hws@denx.de>
> ---
> 
> Notes:
>     I have tested this in an ongoing project and it seems to work
>     reliably.  For some reason WIC creates an extended partition of
>     type `f` but this can't be kept because while fdisk can read it,
>     it is only happy about writing the EBR with type `5`.

Wikipedia says about 0x5:

"Extended partition with CHS addressing. It must reside within the first
physical 8 GB of disk, else use 0Fh instead"

So we likely need to account for that case as well.

>     
>     While probably a very uncommon layout, I am not sure how this
>     would behave when the EBR is not the last partition, but
>     somewhere in between.  I am a bit worried it would silently wreak
>     havoc ...

We should probably throw some test patterns at that. Could be done
against a disk image file as well, I suppose.

> 
>  .../expand-on-first-boot/files/expand-last-partition.sh      | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/meta/recipes-support/expand-on-first-boot/files/expand-last-partition.sh b/meta/recipes-support/expand-on-first-boot/files/expand-last-partition.sh
> index 08c69db30529..ddf1a089e87d 100755
> --- a/meta/recipes-support/expand-on-first-boot/files/expand-last-partition.sh
> +++ b/meta/recipes-support/expand-on-first-boot/files/expand-last-partition.sh
> @@ -17,12 +17,13 @@ if [ "${ROOT_DEV}" = "${BOOT_DEV}" ]; then
>  	exit 1
>  fi
>  
> -LAST_PART="$(sfdisk -d ${BOOT_DEV} 2>/dev/null | tail -1 | cut -d ' ' -f 1)"
> +LAST_PART="$(sfdisk -d "${BOOT_DEV}" 2>/dev/null | tail -1 | cut -d ' ' -f 1)"
>  
>  # Remove all hints to the current medium (last-lba) and last partition size,
>  # then ask sfdisk to recreate the partitioning

The comment should likely be updated as well.

>  sfdisk -d "${BOOT_DEV}" 2>/dev/null | grep -v last-lba | \
> -	sed 's|\('"${LAST_PART}"' .*, \)size=[^,]*, |\1|' | \
> +	sed 's|^\(.*, \)size=[^,]*, type=[f5]$|\1type=5|' | \
> +	sed 's|^\('"${LAST_PART}"' .*, \)size=[^,]*, |\1|' | \

Would it make things worse or better to combine both sed expressions
into the same sed call?

>  	sfdisk --force "${BOOT_DEV}"
>  
>  # Inform the kernel about the partitioning change
> 

Jan

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