stage2: 99-elf-stats for squashfs tuning

This kind of test was proposed by led@ to gather statistics
on chroot's contents going to become squashfs (the script
optimizations lowering added overhead from ~10 sec down
to a subsecond range were also proposed by him).

Intentionally not documented in doc/variables.txt due to
the rather lowlevel nature of the probe (at least so far).

The knobs involved are SQUASHFS (the additional effort kicks
in only for "tight" case) and GLOBAL_SQUASHFS_SORT (must be
non-empty for this extra overhead to occur).

Additional experimentation is needed to find out whether
the difference in squashfs size and performance is worth
the trouble (seems the impact is non-zero but pretty minor).

sub.in/stage2/Makefile

@@ -31,17 +31,29 @@ $(error STAGE1_KFLAVOUR is utterly empty; cannot guess either)
 endif
 
 # need kernel modules only (which require corresponding kernel-image);
-# these go into work chroot; NB: no vmlinuz there
+# these go into work chroot; NB: no vmlinuz there (unless live-install)
 IMAGE_PACKAGES_REGEXP = $(call kpackages, \
 			$(STAGE1_KMODULES) $(STAGE2_KMODULES), \
 			$(STAGE1_KFLAVOUR))
 
+# see also scripts.d/99-elf-stats
+ifdef GLOBAL_SQUASHFS_SORT
+ifeq (tight,$(SQUASHFS))
+CHROOT_PACKAGES += file
+pack-image: PACK_SQUASHFS_OPTS += -sort /.our/elf.lst
+pack-image: CLEANUP_OUTDIR=
+endif
+endif
+
+GLOBAL_SQUASHFS := $(SQUASHFS)
+
 include $(MKIMAGE_PREFIX)/targets.mk
 
 # NB: it's a collector variable, add()ing to a GLOBAL_ results in lost hair
 GLOBAL_CLEANUP_PACKAGES := $(CLEANUP_PACKAGES)
 
-all: | $(GLOBAL_DEBUG) build-image run-image-scripts pack-image \
+all: |  $(GLOBAL_DEBUG) \
+	build-image run-image-scripts run-scripts pack-image \
 	$(GLOBAL_CLEAN_WORKDIR)
 
 # dummy

sub.in/stage2/scripts.d/99-elf-stats

@@ -0,0 +1,48 @@
+#!/bin/sh -e
+# tally up sizes of chroot's ELF binaries for squashfs tuning
+
+# NB: it's unclear so far whether mksquashfs -sort is beneficial
+if [ -z "$GLOBAL_SQUASHFS_SORT" -o "$GLOBAL_SQUASHFS" != "tight" ]; then
+	echo "SKIP elf-stats: looks like it's not needed" >&2
+	exit 0
+fi
+
+exit_handler()
+{
+	local rc=$1
+	rm -f -- "$TMPFILE"
+	exit $rc
+}
+
+# it's controlled environment
+TMPFILE="$(mktemp)"
+
+trap 'exit_handler $?' EXIT HUP PIPE INT QUIT TERM
+
+# a list of ELF binaries (both executables and shared libraries)
+ELFLIST=/.our/elf.lst
+
+cd "$WORKDIR"
+
+# let's parallelize a bit, chroot should be on tmpfs or just-cached
+du -bsx | cut -f1 > "$TMPFILE" &
+
+elf="$(find {,usr/}{lib*,{,s}bin} \
+		-path lib/modules -prune -o \
+		-path usr/lib/locale -prune -o \
+		-type f \
+	| file -nN -e ascii -e compress -e tar -e elf -f - \
+	| sed -n "/: ELF /s/: .*$//p" \
+	| tee "$ELFLIST.in" \
+	| tr '\n' '\0' \
+	| du -cb --files0-from=- \
+	| tail -1 \
+	| cut -f1)"
+
+wait
+read root < "$TMPFILE"
+
+echo "** live chroot ELF ratio: $((100*$elf/$root))% ($elf/$root)" >&2
+
+# add priorities
+sed 's,^.*$,& 1,' < "$ELFLIST.in" > "$ELFLIST"