opkg: Save /bin/busybox and make links

This works around a regression in opkg-lede that thoroughly breaks
upgrading the busybox package and also allows all of busybox's utility
links to be managed using update-alternatives.

/bin/busybox is copied instead of hard linked, because /var might be on
a separate file system (e.g. tmpfs).

2 files changed, 51 insertions, 4 deletions

diff --git a/changelog b/changelog
index d14b168..c72e1be 100644
--- a/changelog
+++ b/changelog
@@ -1,8 +1,12 @@
 opkg-lede (0+git20190131.d4ba162-7) trunk
 
-  * opkg-lede: Add a multiarch support wrapper script as "/usr/bin/opkg"
-    and move the real opkg binary back to its default location at
-    "/usr/bin/opkg-cl".
+  * opkg-lede: Add a wrapper script as "/usr/bin/opkg" and move the real
+    opkg binary back to its default location at "/usr/bin/opkg-cl".
+    This wrapper script:
+    - Enables the busybox package to be safely upgraded (opkg-lede
+      attempts to execute gzip after removing busybox, whereas opkg
+      didn't) and
+    - Accepts an -a/--host-architecture option for multiarch support.
 
  -- Patrick McDermott <patrick.mcdermott@libiquity.com>  Thu, 18 Jun 2020 12:50:01 -0400
 
diff --git a/opkg b/opkg
index 54e2886..33ec19f 100755
--- a/opkg
+++ b/opkg
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/busybox sh
 #
 # opkg - Multiarch support wrapper for opkg
 #
@@ -19,6 +19,45 @@
 
 set -eu
 
+BB='/bin/busybox'
+BIN='/var/lib/opkg/bin'
+
+save_bb()
+{
+	local file=
+	local link=
+	local name=
+	local prio=
+
+	"${BB}" mkdir "${BIN}" 2>/dev/null || :
+	"${BB}" cp -p "${BB}" "${BIN}/busybox"
+
+	while read file; do
+		case "${file}" in
+			/bin/busybox) ;;
+			/bin/?* | /sbin/?* | /usr/bin/?* | /usr/sbin/?*)
+				"${BB}" ln -sf 'busybox' "${BIN}/${file##*/}"
+				;;
+		esac
+	done 0<<-EOF
+		$(/usr/bin/opkg-cl files busybox)
+		EOF
+
+	while read link name prio; do
+		"${BB}" ln -sf 'busybox' "${BIN}/${link##*/}"
+	done 0</usr/share/busybox/alternatives
+
+	export PATH="${PATH}:${BIN}"
+	export OPKG_BUSYBOX_SAVED='1'
+
+	return 0
+}
+
+unsave_bb()
+{
+	rm -f "${BIN}/"*
+}
+
 main()
 {
 	local first_arg=
@@ -80,9 +119,13 @@ main()
 		return 1
 	fi
 
+	save_bb
+
 	if /usr/bin/opkg-cl "${@}"; then
+		unsave_bb
 		return 0
 	else
+		unsave_bb
 		return ${?}
 	fi
 }