feat(padcpio): new helper binary for cpio data alignment

1. Purpose
Improve cpio archive creation performance and space efficiency by
ensuring that file data is aligned within the archive to the filesystem
block size.
For filesystems supporting reflinks (e.g. XFS and Btrfs) this ensures
that cpio archive data can share the same copy-on-write extents as the
archive source files. A GNU cpio binary capable of copy-on-write cloning
data via copy_file_range is required to make proper use of this.

Padding can't be added to cpio archives arbitrarily, so we need to
inject extra files into the archive to provide filesystem alignment.

2. Behaviour
Read a zero terminated file list from stdin. If an input file, when cpio
serialized, is aligned to <padding alignment order> then print it to
stdout.
If the cpio archived file data would be unaligned then create a padding
file in <pad dir> which, when cpio archived before the input file, will
provide cpio alignment and print the pad file path before the input file
path. GNU cpio reorders hardlinks, so avoid extra complexity by
deferring them (unpadded) to the end of the archive.

Signed-off-by: David Disseldorp <ddiss@suse.de>

Author: ddiss

Makefile

@@ -51,7 +51,7 @@ manpages = $(man1pages) $(man5pages) $(man7pages) $(man8pages)
 
 .PHONY: install clean archive rpm srpm testimage test all check AUTHORS CONTRIBUTORS doc dracut-version.sh
 
-all: dracut-version.sh dracut.pc dracut-install skipcpio/skipcpio dracut-util
+all: dracut-version.sh dracut.pc dracut-install skipcpio/skipcpio skipcpio/padcpio dracut-util
 
 %.o : %.c
 	$(CC) -c $(CFLAGS) $(CPPFLAGS) $(KMOD_CFLAGS) $< -o $@
@@ -85,6 +85,9 @@ SKIPCPIO_OBJECTS = skipcpio/skipcpio.o
 skipcpio/skipcpio.o: skipcpio/skipcpio.c
 skipcpio/skipcpio: $(SKIPCPIO_OBJECTS)
 
+skipcpio/padcpio.o: skipcpio/padcpio.c
+skipcpio/padcpio: skipcpio/padcpio.o
+
 UTIL_OBJECTS = util/util.o
 util/util.o: util/util.c
 util/util: $(UTIL_OBJECTS)
@@ -193,6 +196,9 @@ endif
 	if [ -f skipcpio/skipcpio ]; then \
 		install -m 0755 skipcpio/skipcpio $(DESTDIR)$(pkglibdir)/skipcpio; \
 	fi
+	if [ -f skipcpio/padcpio ]; then \
+		install -m 0755 skipcpio/padcpio $(DESTDIR)$(pkglibdir)/padcpio; \
+	fi
 	if [ -f dracut-util ]; then \
 		install -m 0755 dracut-util $(DESTDIR)$(pkglibdir)/dracut-util; \
 	fi
@@ -218,7 +224,7 @@ clean:
 	$(RM) dracut-*.rpm dracut-*.tar.bz2 dracut-*.tar.xz
 	$(RM) dracut-version.sh
 	$(RM) dracut-install install/dracut-install $(DRACUT_INSTALL_OBJECTS)
-	$(RM) skipcpio/skipcpio $(SKIPCPIO_OBJECTS)
+	$(RM) skipcpio/skipcpio $(SKIPCPIO_OBJECTS) skipcpio/padcpio skipcpio/padcpio.o
 	$(RM) dracut-util util/util $(UTIL_OBJECTS)
 	$(RM) $(manpages) dracut.html
 	$(RM) dracut.pc

dracut.spec

@@ -298,6 +298,7 @@ echo 'dracut_rescue_image="yes"' > $RPM_BUILD_ROOT%{dracutlibdir}/dracut.conf.d/
 %{dracutlibdir}/dracut-install
 %{dracutlibdir}/dracut-util
 %{dracutlibdir}/skipcpio
+%{dracutlibdir}/padcpio
 %config(noreplace) %{_sysconfdir}/dracut.conf
 %if 0%{?fedora} || 0%{?suse_version} || 0%{?rhel}
 %{dracutlibdir}/dracut.conf.d/01-dist.conf