Allow for custom image partition schemes.

This commit provides preliminary support for custom partitioning schemes/image file types.
For discussion refer to: issue #10:
#10

This change assumes some artefacts provided by PR #28 are available:
#28
Specifically: br_image_dir() and br_image_path() functions.

This change does **not** address integration within brickstrap.sh itself (should be trivial, though).

brickstrap-image.sh

@@ -0,0 +1,180 @@
+#!/bin/bash
+#
+# This file is part of brickstrap.
+#
+# brickstrap - create a foreign architecture rootfs using kernel namespaces,
+#              multistrap, and qemu usermode emulation and create a disk image
+#              using libguestfs
+#
+# Copyright (C) 2016 Johan Ouwerkerk <[email protected]>
+#
+
+#
+# Note: this file is not meant to be executed, source it as a library of
+# functions instead. Variables used by the functions (other than stack) are
+# namespaced using the 'BR_' or 'BRP_' prefixes. Function names are namespaced
+# similarly, using the 'br_' and 'brp_' prefixes. See docs/namespacing.md for
+# more information on namespacing in brickstrap.
+#
+
+#
+# Default image type 'driver'.
+# This function creates a 'boot+root' MBR type image (type extension: img).
+# $1: path to the image file to generate.
+#
+function brp_image_default_driver()
+{
+    debug "IMAGE_FILE_SIZE: ${IMAGE_FILE_SIZE}"
+    [ $# -eq 1 -a -n "$1" ] && guestfish -N \
+        "$1"=bootroot:vfat:ext4:${IMAGE_FILE_SIZE}:48M:mbr \
+        part-set-mbr-id /dev/sda 1 0x0b : \
+        set-label /dev/sda2 EV3_FILESYS : \
+        mount /dev/sda2 / : \
+        tar-in "$(br_tarball_path)" / : \
+        mkdir-p /media/mmc_p1 : \
+        mount /dev/sda1 /media/mmc_p1 : \
+        glob mv /boot/flash/* /media/mmc_p1/ : \
+
+    # Hack to set the volume label on the vfat partition since guestfish does
+    # not know how to do that. Must be null padded to exactly 11 bytes.
+    echo -e -n "EV3_BOOT\0\0\0" | \
+        dd of="$1" bs=1 seek=32811 count=11 conv=notrunc >/dev/null 2>&1
+}
+
+#
+# Displays an error message if a image type driver failed to create an image
+# file successfully. Returns the given status code.
+# $1: the status code returned by the driver function
+# $2: the name of the partitioning/imaging scheme implemented in the disk image
+# $3: the file path of the disk image
+#
+function brp_image_err_msg()
+{
+    error "Unable to create image: '$3'.
+Driver ($(brp_get_image_type_driver "$2")) returned status code: $1"
+    return $1
+}
+
+#
+# Create a disk image file (type). This function looks up the
+# relevant driver and invokes it with the given path. Before creating the image
+# this function checks it does not already exist or, if it does, that it may be
+# overwritten.
+# $1: the name of the partitioning/imaging scheme implemented in the disk image
+#
+function brp_create_image_type()
+{
+    if [ $# -eq 0 -o -z "$1" ]; then
+        error "Image type required!"
+        return 1
+    elif [ -z "$(brp_get_image_type_driver "$1")" ]; then
+        error "Unable to create image: '$2'.
+No driver for image type: '$1'"
+        return 1
+    fi
+    BRP_CUR_IMG=$(br_image_path "$1" "$(brp_get_image_type_extension $1)")
+    debug "IMAGE: $BRP_CUR_IMG"
+    if [ -z "$BR_FORCE" -a -f "$BRP_CUR_IMG" ]; then
+        error "$BRP_CUR_IMG already exists. Use -f option to overwrite."
+        return 1
+    else
+        eval "$(brp_get_image_type_driver "$1")" "$BRP_CUR_IMG" || \
+            brp_image_err_msg "$?" "$1" "$BRP_CUR_IMG"
+    fi
+}
+
+#
+# Look up the driver function for a given image type name.
+# $1: the name of the partitioning/imaging scheme implemented in the disk image
+#
+function brp_get_image_type_driver()
+{
+    [ $# -eq 1 -a -n "$1" ] && case "$1" in
+        default)
+            echo -n brp_image_default_driver
+        *)
+            eval echo -n "\$BRP_IMG_DRV_REGISTRY_$1"
+    esac
+}
+
+#
+# Look up the file type extension for a given image type name.
+# $1: the name of the partitioning/imaging scheme implemented in the disk image
+#
+function brp_get_image_type_extension()
+{
+    [ $# -eq 1 -a -n "$1" ] && case "$1" in
+        default)
+            echo -n img
+        *)
+            eval echo -n "\$BRP_IMG_EXT_REGISTRY_$1"
+    esac
+}
+
+#
+# Register a custom driver with brickstrap for a custom image type.
+# $1: the name of the partitioning/imaging scheme implemented in the disk image
+# $2: name of the function which will create the image (type), taking the image
+#     file path as argument.
+# $3: the image file type extension, without leading dot.
+#
+function br_register_image_type()
+{
+    [ $# -eq 3 -a -n "$1" -a -n "$2" -a -n "$3" ] && \
+    if [ -z "$(brp_get_image_type_driver "$1")" ]; then
+        eval "BRP_IMG_DRV_REGISTRY_$1=$2"
+        eval "BRP_IMG_EXT_REGISTRY_$1=$3"
+    else
+        fail "Rejected duplicate driver '$2' for image type: '$1'
+Previous setting was: $(brp_get_image_type_driver "$1")"
+    fi
+}
+
+#
+# Creates disk image files for a given list of image types to create.
+# $1: list of image types for which an image file should be created
+# $2: list of previously created images (if applicable). This is used to avoid
+#    attempting to generate the same image twice.
+#
+function brp_create_image_types()
+{
+    BRP_IMAGE_TYPE_RETURN_CODE=0
+    [ $# -eq 1 -a -n "$1" ] && for BRP_CUR_IMG in "$1"; do
+        eval BRP_CUR_IMG="$BRP_CUR_IMG"
+        echo "$2" | fgrep -q "'$BRP_CUR_IMG'" || \
+            brp_create_image_type "$BRP_CUR_IMG" || \
+                BRP_IMAGE_TYPE_RETURN_CODE=$?
+    done && return $BRP_IMAGE_TYPE_RETURN_CODE
+}
+
+#
+# Creates disk images for the configured image types.
+#
+function brp_create_images()
+{
+    info "Creating image files..."
+    debug "TARBALL: $(br_tarball_path)"
+    [ ! -f "$(br_tarball_path)" ] && fail "Could not find $(br_tarball_path)"
+
+    # source custom-image driver scripts
+    if br_list_paths custom-image -r >/dev/null; then
+        br_for_each_path "$(br_list_paths custom-image -r)" brp_run_hook_impl \
+            'loading'
+    fi
+
+    mkdir -p "$(br_image_dir)"
+
+    BRP_IMAGE_RETURN_CODE=0
+    if [ -n "$BR_IMAGE_TYPES" ]; then
+        brp_create_image_types "$BR_IMAGE_TYPES" || BRP_IMAGE_RETURN_CODE=$?
+    fi
+    if [ -n "$IMAGE_TYPES" ]; then
+        brp_create_image_types "$IMAGE_TYPES" "$BR_IMAGE_TYPES" || \
+            BRP_IMAGE_RETURN_CODE=$?
+    fi
+    if [ -z "$BR_IMAGE_TYPES" -a -z "$IMAGE_TYPES" ]; then
+        brp_create_image_type img || BRP_IMAGE_RETURN_CODE=$?
+    fi
+
+    return $BRP_IMAGE_RETURN_CODE
+}