Add support for controlling rootfs size with `IMAGE_*` variables.

* `IMAGE_ROOTFS_SIZE` - The base size of the rootfs. The other two
  variables modify this value

* `IMAGE_ROOTFS_EXTRA_SIZE` - The amount of free space to add to the
  base size of the rootfs

* `IMAGE_OVERHEAD_FACTOR` - Factor determining the amount of free
  space to add to the base size of the rootfs

The final size will be the largest of the two calculations. Please see
the `mender_convert_config` file comments for more information.

Changelog: Commit

Signed-off-by: Kristian Amlie <kristian.amlie@northern.tech>

configs/mender_convert_config

@@ -127,6 +127,41 @@ MENDER_USE_BMAP="n"
 # In most cases you would like this enabled.
 MENDER_COPY_BOOT_GAP="y"
 
+# The size of each of the two rootfs filesystems, in KiB. If this is 0,
+# mender-convert will use the size of the filesystem content as a basis. If the
+# value is -1, mender-convert will use the maximum size that will fit inside the
+# created partition. The size is further modified by IMAGE_ROOTFS_EXTRA_SPACE
+# and IMAGE_OVERHEAD_FACTOR.
+#
+# This variable directly mirrors the variable from the Yocto Project, which is
+# why it is missing a "MENDER_" prefix.
+IMAGE_ROOTFS_SIZE="0"
+
+# The amount of extra free space requested on the rootfs, in KiB. This is added
+# to the value of IMAGE_ROOTFS_SIZE. The size is further modified by
+# IMAGE_OVERHEAD_FACTOR.
+#
+# Note that due to reserved space for the root user on the filesystem, "df" may
+# report a significantly lower number than requested. A more accurate number can
+# be fetched using for example "dumpe2fs" and looking for the "Free blocks"
+# field, but even this value is usually going to be lower than requested due to
+# meta data on the filesystem.
+#
+# This variable directly mirrors the variable from the Yocto Project, which is
+# why it is missing a "MENDER_" prefix.
+IMAGE_ROOTFS_EXTRA_SPACE="0"
+
+# This factor is multiplied by the used space value for the generated rootfs,
+# and if the result is larger than IMAGE_ROOTFS_SIZE + IMAGE_ROOTFS_EXTRA_SPACE,
+# it will be used as the size of the rootfs instead of the other two variables.
+#
+# The actual free space will usually be lower than requested. See comment for
+# IMAGE_ROOTFS_EXTRA_SPACE.
+#
+# This variable directly mirrors the variable from the Yocto Project, which is
+# why it is missing a "MENDER_" prefix.
+IMAGE_OVERHEAD_FACTOR="1.5"
+
 source configs/mender_grub_config
 
 # Function to create Mender Artifact

mender-convert-package

@@ -142,15 +142,32 @@ image_name="${device_type}-${artifact_name}"
 
 actual_rootfs_size=$(sudo du -s --block-size=512 work/rootfs | cut -f 1)
 
-# 50 % free space, not to be confused with rootfs_part_sectors
-rootfs_image_sectors=$(awk -v r1="$actual_rootfs_size" 'BEGIN{printf "%.0f", r1 * 1.50}')
+# KiB -> 512 sectors
+image_rootfs_size_sectors=$((${IMAGE_ROOTFS_SIZE} * 2))
+
+if [ "${IMAGE_ROOTFS_SIZE}" -eq -1 ]; then
+  rootfs_image_sectors="${rootfs_part_sectors}"
+elif [ "${image_rootfs_size_sectors}" -lt "${actual_rootfs_size}" ]; then
+  rootfs_image_sectors="${actual_rootfs_size}"
+else
+  rootfs_image_sectors="${image_rootfs_size_sectors}"
+fi
+
+rootfs_image_sectors=$((${rootfs_image_sectors} + ${IMAGE_ROOTFS_EXTRA_SPACE} * 2))
+
+rootfs_image_sectors_overhead=$(awk -v r1="$actual_rootfs_size" "BEGIN{printf \"%.0f\", r1 * ${IMAGE_OVERHEAD_FACTOR}}")
+if [ "${rootfs_image_sectors_overhead}" -gt "${rootfs_image_sectors}" ]; then
+  rootfs_image_sectors="${rootfs_image_sectors_overhead}"
+fi
 
 if [ ${rootfs_image_sectors} -gt ${rootfs_part_sectors} ]; then
   log_warn "The calculated rootfs partition size $(disk_sectors_to_mb ${rootfs_part_sectors}) MiB is too small."
   log_warn "The actual rootfs image size is $(disk_sectors_to_mb ${rootfs_image_sectors}) MiB"
-  log_fatal "You can try adjusting the MENDER_STORAGE_TOTAL_SIZE_MB variable to increase available space"
+  log_fatal "You can try adjusting the MENDER_STORAGE_TOTAL_SIZE_MB variable to increase available space, or modify one of the variables IMAGE_ROOTFS_SIZE, IMAGE_ROOTFS_EXTRA_SPACE or IMAGE_OVERHEAD_FACTOR to reduce the size of the root filesystem."
 fi
 
+log_info "Rootfs filesystem size will be $(disk_sectors_to_mb ${rootfs_image_sectors}) MiB"
+
 # Extract file-system type from rootfs
 if file ${root_part} | grep -q ext4; then
   image_fs_type="ext4"