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

[Harald Seiler <hws@denx.de>]

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.

 .../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.
+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
-- 
2.25.4