[source] x86: sysupgrade: move partition table change check to platform_check_image

[LEDE Commits]

neoraider pushed a commit to source.git, branch master:
https://git.lede-project.org/19b84cfff26e4feae8ce4bbbb76567474d975d59

commit 19b84cfff26e4feae8ce4bbbb76567474d975d59
Author: Matthias Schiffer <mschiffer at universe-factory.net>
AuthorDate: Wed May 3 08:57:29 2017 +0200

    x86: sysupgrade: move partition table change check to platform_check_image
    
    The staged sysupgrade will prevent us from using ask_bool in
    platform_do_upgrade; therefore, the check is moved to platform_check_image.
    
    Signed-off-by: Matthias Schiffer <mschiffer at universe-factory.net>
---
 .../linux/x86/base-files/lib/upgrade/platform.sh   | 29 +++++++++++++++++++---
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/target/linux/x86/base-files/lib/upgrade/platform.sh b/target/linux/x86/base-files/lib/upgrade/platform.sh
index d3e9f36..81b349a 100644
--- a/target/linux/x86/base-files/lib/upgrade/platform.sh
+++ b/target/linux/x86/base-files/lib/upgrade/platform.sh
@@ -1,13 +1,37 @@
 platform_check_image() {
+	local diskdev partdev diff
 	[ "$#" -gt 1 ] && return 1
 
 	case "$(get_magic_word "$1")" in
-		eb48|eb63) return 0;;
+		eb48|eb63) ;;
 		*)
 			echo "Invalid image type"
 			return 1
 		;;
 	esac
+
+	export_bootdevice && export_partdevice diskdev 0 || {
+		echo "Unable to determine upgrade device"
+		return 1
+	}
+
+	get_partitions "/dev/$diskdev" bootdisk
+
+	#extract the boot sector from the image
+	get_image "$@" | dd of=/tmp/image.bs count=1 bs=512b 2>/dev/null
+
+	get_partitions /tmp/image.bs image
+
+	#compare tables
+	diff="$(grep -F -x -v -f /tmp/partmap.bootdisk /tmp/partmap.image)"
+
+	rm -f /tmp/image.bs /tmp/partmap.bootdisk /tmp/partmap.image
+
+	if [ -n "$diff" ]; then
+		echo "Partition layout has changed. Full image will be written."
+		ask_bool 0 "Abort" && exit 1
+		return 0
+	fi
 }
 
 platform_copy_config() {
@@ -36,9 +60,6 @@ platform_do_upgrade() {
 			#compare tables
 			diff="$(grep -F -x -v -f /tmp/partmap.bootdisk /tmp/partmap.image)"
 			if [ -n "$diff" ]; then
-				echo "Partition layout is changed.  Full image will be written."
-				ask_bool 0 "Abort" && exit
-
 				get_image "$@" | dd of="/dev/$diskdev" bs=4096 conv=fsync
 				return 0
 			fi