Bug#803115: flash-kernel: please provide an option to disable creation of backup files

[Eric Cooper <ecc@cooper-siegel.org>]

Package: flash-kernel
Version: 3.48
Followup-For: Bug #803115

Here's a patch, tested on my Seagate Dockstar.

Default behavior:
    $ sudo flash-kernel
    DTB: kirkwood-dockstar.dtb
    Installing kirkwood-dockstar.dtb into /boot/dtbs/4.2.0-0.bpo.1-kirkwood/kirkwood-dockstar.dtb
    Taking backup of kirkwood-dockstar.dtb.
    Installing new kirkwood-dockstar.dtb.
    flash-kernel: installing version 4.2.0-0.bpo.1-kirkwood
    flash-kernel: appending /usr/lib/linux-image-4.2.0-0.bpo.1-kirkwood/kirkwood-dockstar.dtb to kernel
    Generating kernel u-boot image... done.
    Taking backup of uImage.
    Installing new uImage.
    Generating initramfs u-boot image... done.
    Taking backup of uInitrd.
    Installing new uInitrd.
    Taking backup of dtb.
    Installing new dtb.

New behavior with NO_BACKUP_FILES=true set in /etc/default/flash-kernel:

    $ sudo flash-kernel
    DTB: kirkwood-dockstar.dtb
    Installing kirkwood-dockstar.dtb into /boot/dtbs/4.2.0-0.bpo.1-kirkwood/kirkwood-dockstar.dtb
    Skipping backup of kirkwood-dockstar.dtb.
    Installing new kirkwood-dockstar.dtb.
    flash-kernel: installing version 4.2.0-0.bpo.1-kirkwood
    flash-kernel: appending /usr/lib/linux-image-4.2.0-0.bpo.1-kirkwood/kirkwood-dockstar.dtb to kernel
    Generating kernel u-boot image... done.
    Skipping backup of uImage.
    Installing new uImage.
    Generating initramfs u-boot image... done.
    Skipping backup of uInitrd.
    Installing new uInitrd.
    Skipping backup of dtb.
    Installing new dtb.

>From e111d107a0e9453d0af0eb0ed4708a1aea1f901e Mon Sep 17 00:00:00 2001
From: Eric Cooper <ecc@cmu.edu>
Date: Sat, 7 Nov 2015 13:15:39 -0500
Subject: [PATCH] Add NO_BACKUP_FILES option to /etc/default/flash-kernel.

If set, no backups of kernel, initrd, and dtb files will be created,
to save space on systems with limited storage.

Signed-off-by: Eric Cooper <ecc@cmu.edu>
---
 README    |  9 ++++++---
 functions | 18 ++++++++++++++++--
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/README b/README
index 4ca5a22..bc7493c 100644
--- a/README
+++ b/README
@@ -191,9 +191,12 @@ Configuration files currently supported:
   script snippets. See "Adding U-Boot Commands for Pre-Boot Execution"
   below for more details.
 
-* /etc/default/flash-kernel currently contains a single variable,
-  LINUX_KERNEL_CMDLINE, which should be used by bootscripts to set kernel
-  options.
+* /etc/default/flash-kernel currently contains the following variables:
+    - LINUX_KERNEL_CMDLINE, which should be used by bootscripts to set kernel
+      options.
+    - NO_BACKUP_FILES, which if set to "true" or "yes" will prevent
+      flash-kernel from creating backup versions of kernel, initrd,
+      and dtb files.
 
 
 Adding U-Boot Commands for Pre-Boot Execution
diff --git a/functions b/functions
index 35d872b..9bbef2c 100644
--- a/functions
+++ b/functions
@@ -404,13 +404,27 @@ mkimage_multi() {
 	echo "done." >&2
 }
 
+# Return a nonempty string *unless* NO_BACKUP_FILES is set.
+get_backup_preference() {
+        . /etc/default/flash-kernel
+	case $(echo "$NO_BACKUP_FILES" | tr '[:upper:]' '[:lower:]') in
+	    true|yes|1) ;;
+	    *) echo yes ;;
+	esac
+}
+
 backup_and_install() {
 	local source="$1"
 	local dest="$2"
+	local do_backups=$(get_backup_preference)
 
 	if [ -e "$dest" ]; then
-		echo "Taking backup of $(basename "$dest")." >&2
-		mv "$dest" "$dest.bak"
+		if [ -n "$do_backups" ]; then
+			echo "Taking backup of $(basename "$dest")." >&2
+			mv "$dest" "$dest.bak"
+		else
+			echo "Skipping backup of $(basename "$dest")." >&2
+		fi
 	fi
 	echo "Installing new $(basename "$dest")." >&2
 	mv "$source" "$dest"
-- 
2.6.2