Re: [PATCH v2] expand-on-first-boot: Allow expanding extended MBR partitions

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

On 15.06.20 12:10, 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:
>     Changes in v2:
>     - Keep a type `f` EBR as type `f`.
>     - Update comment to better explain what is done.
>     
>     I've built myself a little test-suite to see how this script
>     behaves when given different layouts.  It seems to work just fine
>     now for the following cases:
>     
>     - Expanding last partition of a GPT.
>     - Expanding last partition of an MBR without extended partitions.
>     - Expanding last (logical) partition of an MBR when the last
>       primary partition is the EBR.
>     
>     Having the EBR somewhere in the middle is *not* supported.  The
>     script will fail with an error message, without accidentally
>     ruining the layout.  I think such a case is too rare to be worth
>     supporting.

Ack.

> 
>  .../files/expand-last-partition.sh             | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 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..7175dfd38b7e 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 +17,20 @@ 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 "${BOOT_DEV}" 2>/dev/null | tail -1 | cut -d ' ' -f 1)"
>  
> -# Remove all hints to the current medium (last-lba) and last partition size,
> -# then ask sfdisk to recreate the partitioning
> -sfdisk -d "${BOOT_DEV}" 2>/dev/null | grep -v last-lba | \
> -	sed 's|\('"${LAST_PART}"' .*, \)size=[^,]*, |\1|' | \
> +# Transform the partition table as follows:
> +#
> +# - Remove any 'last-lba' header so sfdisk uses the entire available space.
> +# - If this partition table is MBR and an extended partition container (EBR)
> +#   exists, we assume this needs to be expanded as well; remove its size
> +#   field so sfdisk expands it.
> +# - For the previously fetched last partition, also remove the size field so
> +#   sfdisk expands it.

Very nice.

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

LGTM.

Jan

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