e2k: add /write.sh into ISO images

There's some peculiarity in writing ISO images for e2k
onto USB Flash media: we need to arrange a partition
and ext2 filesystem with its label passed to propagator;
the former part is what's expected, and the latter one
is what this script does.

Thanks to aerodisk.ru guys for catching a brown paper bag
class typo making format() try to affect the image and not
the drive, by the way.

features.in/e2k/lib/50-e2k-write.sh

@@ -0,0 +1,46 @@
+#!/bin/sh -efu
+# ALT: write Elbrus boot media
+# public domain 2020 Michael Shigorin <mike@altlinux.org>
+
+error() { echo "$@" >&2; exit 1; }
+usage() { error "Usage: $0 /path/to/alt-e2k.iso /dev/sdX1_or_/dev/sr0"; }
+
+[ $# = 2  ] || usage
+[ -s "$1" ] || usage
+[ -b "$2" ] || usage
+
+checkuid() { [ "$(id -u)" = 0 ] || error "$0: need to run as root"; }
+format() { mkfs.ext2 -E packed_meta_blocks=1,num_backup_sb=1 -L altinst "$1"; }
+
+case "$2" in
+/dev/sr[0-9]*|dvd*|cd*)
+	grep -qw "^$2" /proc/mounts && checkuid && umount -v "$2"
+	echo "Writing DVD image..."
+	growisofs -dvd-compat -Z "$2"="$1"
+	;;
+/dev/sd*)
+	grep -q "^$1" /proc/mounts && error "$1 mounted already"
+	checkuid
+	[ "$(blkid -o value -s LABEL "$2")" = "altinst" ] || format "$2"
+	src="$(mktemp -d)"
+	dst="$(mktemp -d)"
+	echo -n "mounting image... "
+	mount -o loop,ro "$1" "$src"; echo "done"
+	echo -n "mounting drive... "
+	mount -o noatime "$2" "$dst"; echo "done"
+	echo "copying contents..."
+	rsync -Pavc --inplace --delete --numeric-ids "$src/" "$dst/" ||
+		cp -avt "$dst" -- "$src"/{.disk,*}
+	grep -q "^default=.*_flash$" "$dst/boot.conf" || {
+		echo -n "updating default boot target... "
+		sed -i 's,default=install$,&_flash,' "$dst/boot.conf"
+		echo "done"
+	}
+	echo -n "unmounting media... "
+	umount "$src" "$dst"
+	echo "done."
+	;;
+*)
+	usage
+	;;
+esac

features.in/e2k/lib/50-e2k.mk

@@ -0,0 +1,4 @@
+WHATEVER += files/write.sh
+
+files/write.sh:
+	@install -pDm755 lib/50-e2k-write.sh files/write.sh