Implement MENDER_COPY_BOOT_GAP feature

This is necessary for the U-boot -> EFI -> GRUB integration to be
complete as many boards embedd the U-Boot binary at the start
of the SD/eMMC a.k.a boot-gap.

When MENDER_COPY_BOOT_GAP is enabled, it will be copied from the
input disk image to the output ".sdimg"

MEN-2784

Changelog: Title

Signed-off-by: Mirza Krak <mirza.krak@northern.tech>

configs/beaglebone_black_base_config

@@ -6,6 +6,9 @@
 # There are reported issues with GRUB bootloader integration, fallback to U-boot.
 MENDER_GRUB_EFI_INTEGRATION=n
 
+# We will write a modified bootloader
+MENDER_COPY_BOOT_GAP=n
+
 # 4MB alignment
 MENDER_PARTITION_ALIGNMENT="4194304"
 

configs/mender_convert_config

@@ -120,6 +120,13 @@ MENDER_KERNEL_DEVICETREE=kernel.dtb
 #    https://github.com/intel/bmap-tools
 MENDER_USE_BMAP="n"
 
+# Copy the boot gap, which is the area from sector 1 until first parition,
+# this is done because some images might contain the bootloader embedded here
+# and we need to copy the bootloader to the output image.
+#
+# In most cases you would like this enabled.
+MENDER_COPY_BOOT_GAP="y"
+
 source configs/mender_grub_config
 
 # Function to create Mender Artifact

configs/qemux86-64_config

@@ -14,3 +14,6 @@
 
 MENDER_STORAGE_DEVICE=/dev/sda
 MENDER_DEVICE_TYPE="qemux86_64"
+
+# Nothing to copy
+MENDER_COPY_BOOT_GAP="n"

configs/raspberrypi_config

@@ -1,6 +1,9 @@
 # Raspberry Pi does not support GRUB bootloader integration, fallback to U-boot.
 MENDER_GRUB_EFI_INTEGRATION=n
 
+# Nothing to copy
+MENDER_COPY_BOOT_GAP=n
+
 # 4MB alignment
 MENDER_PARTITION_ALIGNMENT="4194304"
 

configs/rockpro64_config

@@ -1,6 +1,9 @@
 # ROCKPro64 do not support GRUB bootloader integration, fallback to U-boot.
 MENDER_GRUB_EFI_INTEGRATION=n
 
+# We will write a modified bootloader
+MENDER_COPY_BOOT_GAP=n
+
 ROCKPRO64_BINARIES_URL="${MENDER_STORAGE_URL}/mender-convert/armbian/rockpro64/${ROCKPRO64_BINARIES}"
 
 function platform_modify() {

mender-convert-extract

@@ -102,5 +102,8 @@ fi
 # this is done because some images might contain the bootloader embedded here
 # and we might need to keep this area intact when we generate our custom
 # image.
-disk_extract_part "${disk_image}" \
-  1 $(( $(disk_get_part_value ${disk_image} 1 START) - 1)) work/boot-gap.bin
+if [ "${MENDER_COPY_BOOT_GAP}" == "y" ]; then
+  log_info "Extracting boot gap to work/boot-gap.bin"
+  disk_extract_part "${disk_image}" \
+    1 $(( $(disk_get_part_value ${disk_image} 1 START) - 1)) work/boot-gap.bin
+fi

mender-convert-package

@@ -102,6 +102,16 @@ else
   overhead_sectors=$(( ${alignment_sectors} * 6 ))
 fi
 
+# Validate boot-gap.bin size, ensuring it will fit between MBR and boot_part_start
+if [ "${MENDER_COPY_BOOT_GAP}" == "y" ]; then
+  # Add one block for MBR
+  boot_gap_sectors=$(( $(stat --printf="%b" work/boot-gap.bin) + 1))
+  if [ ${boot_gap_sectors} -ge ${boot_part_start} ]; then
+    log_warn "The work/boot-gap.bin file will overwrite the boot partition"
+    log_fatal "Please increase MENDER_PARTITION_ALIGNMENT (2x will typically solve this))"
+  fi
+fi
+
 # Validate boot part size
 actual_boot_size=$(du --apparent-size -s --block-size=512 ${boot_part} | cut -f 1)
 if [ ${actual_boot_size} -gt ${boot_part_sectors} ]; then
@@ -199,6 +209,12 @@ run_and_log_cmd "${PARTED} -s ${sdimg_path} -- unit s mkpart primary ext2 ${root
 run_and_log_cmd "${PARTED} -s ${sdimg_path} -- unit s mkpart primary ext2 ${data_start} ${data_end}"
 run_and_log_cmd "${PARTED} -s ${sdimg_path} print"
 
+# Write boot-gap
+if [ "${MENDER_COPY_BOOT_GAP}" == "y" ]; then
+  log_info "Writing boot gap of size: ${boot_part_sectors} (sectors)"
+  disk_write_at_offset "${output_dir}/boot-gap.bin" "${sdimg_path}" "1"
+fi
+
 # Burn Partitions
 disk_write_at_offset "${boot_part}" "${sdimg_path}" "${boot_part_start}"
 disk_write_at_offset "${output_dir}/rootfs.img" "${sdimg_path}" "${rootfsa_start}"