[source] base-files: add a hint in sysupgrade that shows what to do when the image metadata check fails

[LEDE Commits]

nbd pushed a commit to source.git, branch master:
https://git.lede-project.org/81b5e8e5d21437a65ebfb98112a0709f4020af36

commit 81b5e8e5d21437a65ebfb98112a0709f4020af36
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Sat Nov 26 18:43:59 2016 +0100

    base-files: add a hint in sysupgrade that shows what to do when the image metadata check fails
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 package/base-files/files/lib/upgrade/fwtool.sh | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/package/base-files/files/lib/upgrade/fwtool.sh b/package/base-files/files/lib/upgrade/fwtool.sh
index 984c173..49f02b7 100644
--- a/package/base-files/files/lib/upgrade/fwtool.sh
+++ b/package/base-files/files/lib/upgrade/fwtool.sh
@@ -9,6 +9,9 @@ fwtool_check_image() {
 
 	if ! fwtool -q -i /tmp/sysupgrade.meta "$1"; then
 		echo "Image metadata not found"
+		[ "$REQUIRE_IMAGE_METADATA" = 1 -a "$FORCE" != 1 ] && {
+			echo "Use sysupgrade -F to override this check when downgrading or flashing to vendor firmware"
+		}
 		[ "$REQUIRE_IMAGE_METADATA" = 1 ] && return 1
 		return 0
 	fi