Source cleanups.

18 files changed, 502 insertions, 44 deletions

diff --git a/INSTALL b/INSTALL
index e3bc2df..9d98581 100644
--- a/INSTALL
+++ b/INSTALL
@@ -1,4 +1,4 @@
-Use ./configure; make; sudo make test; sudo make install.
+Use ./configure; make; make test; sudo make install.
 
 If building from git, run ./autogen.sh first.
 
diff --git a/LICENSE b/LICENSE
index a2b1204..e0d83e9 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,5 +1,7 @@
 This software is a combination of components distributed under the 3-clause
-BSD, MIT, and FSF unlimited licenses.
+BSD, MIT, and FSF unlimited licenses. Note that libudev, libblkid, and libmount
+are LGPL licensed, so when random-seed is built against those, the terms of the
+LGPL apply for those libraries.
 
 All files that neither have copyright notices at the top nor are listed below
 are distributed under the 3-clause BSD license:
@@ -33,7 +35,9 @@ OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 ---
 
-Autoconf generated files are distributed under the FSF unlimited license located in their respective files (as of writing, aclocal.m4, config.status, configure).
+Autoconf generated files are distributed under the FSF unlimited license
+located in their respective files (as of writing, aclocal.m4, config.status,
+configure).
 
 ---
 
diff --git a/Makefile.in b/Makefile.in
index 455315c..536a372 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -1,7 +1,9 @@
+# SPDX-License-Identifier: BSD-3-Clause
 # @configure_input@
 
 VPATH = @srcdir@:@srcdir@/src
 srcdir = @srcdir@
+abs_builddir = @abs_builddir@
 
 prefix = @prefix@
 exec_prefix = @exec_prefix@
@@ -14,7 +16,7 @@ systemdsystemunitdir = @systemdsystemunitdir@
 default_seed_path_dir = @default_seed_path_dir@
 
 CC = @CC@
-CFLAGS = -Wall -Wextra -pedantic @CFLAGS@ -UNDEBUG -include @abs_builddir@/config.h
+CFLAGS = @CFLAGS@ -UNDEBUG -I$(abs_builddir)
 CPPFLAGS = @CPPFLAGS@
 LDFLAGS = @LDFLAGS@
 
@@ -22,9 +24,12 @@ SRC := random-seed.c sha2.c util.c
 OBJ := $(SRC:.c=.o)
 TEST_FILE := random-seed.test
 
-all: random-seed random-seed.service random-seed-save.service
+all: random-seed systemd/random-seed.service systemd/random-seed-save.service
 
-Makefile: Makefile.in configure.ac
+$(srcdir)/configure: $(srcdir)/aclocal.m4 $(srcdir)/autogen.sh $(srcdir)/configure.ac
+	cd $(srcdir); ./autogen.sh
+
+Makefile: $(srcdir)/configure Makefile.in
 	$(srcdir)/configure
 
 random-seed: $(OBJ)
@@ -35,18 +40,19 @@ util.o: util.c util.h sha2.h
 
 sha2.o: sha2.c sha2.h
 
-random-seed.service random-seed-save.service: Makefile
+systemd/random-seed.service systemd/random-seed-save.service: Makefile
+.in:
 	sed -e 's|@sbindir[@]|$(sbindir)|g' \
 	    -e 's|@default_seed_path_dir[@]|$(default_seed_path_dir)|g' \
 	    $(srcdir)/$@.in > $@
 
 install: all
 	install -D -m755 random-seed $(DESTDIR)$(sbindir)/random-seed
-	install -D -m644 $(srcdir)/random-seed.8 $(DESTDIR)$(mandir)/man8/random-seed.8
+	install -D -m644 $(srcdir)/doc/random-seed.8 $(DESTDIR)$(mandir)/man8/random-seed.8
 ifneq ($(systemdsystemunitdir),)
-	install -D -m644 random-seed.service $(DESTDIR)$(systemdsystemunitdir)/random-seed.service
-	install -D -m644 $(srcdir)/random-seed-save.service $(DESTDIR)$(systemdsystemunitdir)/random-seed-save.service
-	install -D -m644 $(srcdir)/random-seed-save.timer $(DESTDIR)$(systemdsystemunitdir)/random-seed-save.timer
+	install -D -m644 systemd/random-seed.service $(DESTDIR)$(systemdsystemunitdir)/random-seed.service
+	install -D -m644 $(srcdir)/systemd/random-seed-save.service $(DESTDIR)$(systemdsystemunitdir)/random-seed-save.service
+	install -D -m644 $(srcdir)/systemd/random-seed-save.timer $(DESTDIR)$(systemdsystemunitdir)/random-seed-save.timer
 endif
 
 test: $(TEST_FILE)
@@ -56,10 +62,11 @@ $(TEST_FILE): random-seed
 	$(TEST_WRAPPER) ./random-seed load $(TEST_FILE) || [ $$? = 15 ]
 
 clean:
-	$(RM) random-seed random-seed.service random-seed-save.service $(OBJ) $(DEP) $(TEST_FILE)
+	$(RM) random-seed systemd/random-seed.service systemd/random-seed-save.service $(OBJ) $(DEP) $(TEST_FILE)
+	rmdir systemd 2>/dev/null || true
 
 distclean: clean
-	$(RM) -r autom4te.cache config.h config.log config.status Makefile
+	$(RM) -r autom4te.cache config.cache config.h config.log config.status Makefile
 
 .PHONY: all install test clean random-seed.test
 .INTERMEDIATE: $(TEST_FILE)
diff --git a/README b/README
index 6c27edb..1fb5062 100644
--- a/README
+++ b/README
@@ -1,16 +1,14 @@
 random-seed is a random seed management program.  In contrast with other random
 seed implementations, random-seed will credit the random seed to the kernel
 entropy count.  It attempts to prevent inadvertent random seed sharing by
-checking that certain system identifiers, such as the machine ID and filesystem
+checking that certain system identifiers such as the machine ID and filesystem
 ID have not changed between a save and load.  If these identifiers do not
 match, random-seed will still load the random seed, but will not credit the
 entropy.
 
-It is my understanding that other operating systems are either not commonly
-imaged (e.g. BSDs) or have official tools for system image preparation (e.g.
-sysprep for Windows). Therefore, random-seed is Linux specific. However, it
-should be reasonably easy to port by simply adjusting the paths and changing
-getrandom to /dev/random.
+random-seed is intended for distribution use. For a system that is
+administratively guaranteed not to be cloned, consider the random-seed-basic
+project instead.
 
 random-seed requires the following to compile:
 
@@ -18,8 +16,35 @@ random-seed requires the following to compile:
 - GNU make (BSD make is not fine)
 - Bourne-like sh (autoconf compatible, i.e. probably all of them)
 
-If compiling from git, autoconf is also required. random-seed does not use
-automake, gettext, or libtool.
+random-seed also supports linking with libudev or libmount and libblkid. It is
+highly recommended to enable libudev if your target platform includes udevd
+(eudev is supported), as it allows detection of the hard drive ID. Otherwise,
+it is highly recommended to enable libmount and libblkid, as these allow
+reliable detection of the file system UUID. It is assumed that most GNU/Linux
+systems will include the util-linux package that contains these libraries, so
+that should cover almost everybody. Even so, if neither of these are compiled
+in, random-seed will fall back on the statfs(2) system call and use the f_fsid
+field to identify the file system, if the file system type is btrfs, ext2/3/4,
+JFS, NTFS, reiserfs, or UBIFS. If the file system type is none of these, and
+none of the above libraries have been compiled in, random-seed will only use
+the machine ID for cloning detection. However, if you do not have libudev, you
+probably also do not use systemd or dbus, so you will probably not have a
+machine ID. In this case, random-seed will never credit the entropy, so you may
+as well use a "dd if=random-seed of=/dev/urandom" script.
 
-random-seed requires Linux 3.11 or higher supporting the getrandom(2) system
-call.
+When compiling from git, autoconf, aclocal, and autoconf-archive are required.
+aclocal is provided by the automake package on most operating systems. [1]
+
+random-seed is Linux-specific, as it is my understanding that other operating
+systems are either not commonly imaged (e.g. BSDs) or have official tools for
+system image preparation (e.g. sysprep for Windows). However, it should be
+reasonably easy to port by simply adjusting the paths and changing getrandom to
+/dev/random.
+
+random-seed supports a daemonize mode. This is recommended on systems without
+a centralized timer synchronization mechanism similar to Android or systemd.
+random-seed uses under 100 KB of RAM and negligible CPU when daemonized.
+
+[1] Automake has a "Future of aclocal" section in its manual. This section has
+contained the text "aclocal is expected to disappear" since its inception in
+2003, more than 15 years ago as of writing.
diff --git a/autogen.sh b/autogen.sh
index afcd93c..ae9d8c7 100755
--- a/autogen.sh
+++ b/autogen.sh
@@ -1,9 +1,10 @@
 #!/bin/sh
+# SPDX-License-Identifier: BSD-3-Clause
 
 set -e
 
 autoheader &
-aclocal
+aclocal -I m4 --install
 autoconf
 
 wait
diff --git a/configure.ac b/configure.ac
index 813238a..e157917 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,5 +1,10 @@
+# SPDX-License-Identifier: BSD-3-Clause
+
 AC_INIT(random-seed, 0.1)
+AC_CONFIG_MACRO_DIRS([m4])
+
 AC_LANG(C)
+
 AC_CONFIG_HEADERS(config.h)
 AC_PROG_CC
 
@@ -7,7 +12,7 @@ AC_PROG_CC_C99
 AS_IF([test "$ac_cv_prog_cc_c99" = no],
       [AC_MSG_ERROR([a C99 compatible compiler is required])])
 
-CPPFLAGS="$CPPFLAGS -D_GNU_SOURCE -D_DEFAULT_SOURCE -D_POSIX_C_SOURCE=200809L"
+CPPFLAGS="${CPPFLAGS+$CPPFLAGS }-D_GNU_SOURCE -D_DEFAULT_SOURCE -D_POSIX_C_SOURCE=200809L"
 
 PKG_CHECK_VAR(systemdsystemunitdir, systemd, systemdsystemunitdir)
 
@@ -44,4 +49,8 @@ AC_DEFINE_UNQUOTED(DEFAULT_SEED_PATH, "$default_seed_path", [default seed path])
 default_seed_path_dir=${default_seed_path%/*}
 AC_SUBST(default_seed_path_dir)
 
+AX_CHECK_COMPILE_FLAG(-Wall, [CFLAGS="-Wall${CFLAGS+ $CFLAGS}"])
+AX_CHECK_COMPILE_FLAG(-Wextra, [CFLAGS="-Wextra${CFLAGS+ $CFLAGS}"])
+AX_CHECK_COMPILE_FLAG(-pedantic, [CFLAGS="-pedantic${CFLAGS+ $CFLAGS}"])
+
 AC_OUTPUT(Makefile)
diff --git a/random-seed.8 b/doc/random-seed.8
index 484159d..484159d 100644
--- a/random-seed.8
+++ b/doc/random-seed.8
diff --git a/m4/ax_check_compile_flag.m4 b/m4/ax_check_compile_flag.m4
new file mode 100644
index 0000000..dcabb92
--- /dev/null
+++ b/m4/ax_check_compile_flag.m4
@@ -0,0 +1,74 @@
+# ===========================================================================
+#  https://www.gnu.org/software/autoconf-archive/ax_check_compile_flag.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_CHECK_COMPILE_FLAG(FLAG, [ACTION-SUCCESS], [ACTION-FAILURE], [EXTRA-FLAGS], [INPUT])
+#
+# DESCRIPTION
+#
+#   Check whether the given FLAG works with the current language's compiler
+#   or gives an error.  (Warnings, however, are ignored)
+#
+#   ACTION-SUCCESS/ACTION-FAILURE are shell commands to execute on
+#   success/failure.
+#
+#   If EXTRA-FLAGS is defined, it is added to the current language's default
+#   flags (e.g. CFLAGS) when the check is done.  The check is thus made with
+#   the flags: "CFLAGS EXTRA-FLAGS FLAG".  This can for example be used to
+#   force the compiler to issue an error when a bad flag is given.
+#
+#   INPUT gives an alternative input source to AC_COMPILE_IFELSE.
+#
+#   NOTE: Implementation based on AX_CFLAGS_GCC_OPTION. Please keep this
+#   macro in sync with AX_CHECK_{PREPROC,LINK}_FLAG.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
+#   Copyright (c) 2011 Maarten Bosmans <mkbosmans@gmail.com>
+#
+#   This program is free software: you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation, either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <https://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 5
+
+AC_DEFUN([AX_CHECK_COMPILE_FLAG],
+[AC_PREREQ(2.64)dnl for _AC_LANG_PREFIX and AS_VAR_IF
+AS_VAR_PUSHDEF([CACHEVAR],[ax_cv_check_[]_AC_LANG_ABBREV[]flags_$4_$1])dnl
+AC_CACHE_CHECK([whether _AC_LANG compiler accepts $1], CACHEVAR, [
+  ax_check_save_flags=$[]_AC_LANG_PREFIX[]FLAGS
+  _AC_LANG_PREFIX[]FLAGS="$[]_AC_LANG_PREFIX[]FLAGS $4 $1"
+  AC_COMPILE_IFELSE([m4_default([$5],[AC_LANG_PROGRAM()])],
+    [AS_VAR_SET(CACHEVAR,[yes])],
+    [AS_VAR_SET(CACHEVAR,[no])])
+  _AC_LANG_PREFIX[]FLAGS=$ax_check_save_flags])
+AS_VAR_IF(CACHEVAR,yes,
+  [m4_default([$2], :)],
+  [m4_default([$3], :)])
+AS_VAR_POPDEF([CACHEVAR])dnl
+])dnl AX_CHECK_COMPILE_FLAGS
diff --git a/m4/pkg.m4 b/m4/pkg.m4
new file mode 100644
index 0000000..d8549a4
--- /dev/null
+++ b/m4/pkg.m4
@@ -0,0 +1,343 @@
+# pkg.m4 - Macros to locate and utilise pkg-config.   -*- Autoconf -*-
+# serial 11 (pkg-config-0.29.1)
+
+dnl Copyright © 2004 Scott James Remnant <scott@netsplit.com>.
+dnl Copyright © 2012-2015 Dan Nicholson <dbn.lists@gmail.com>
+dnl
+dnl This program is free software; you can redistribute it and/or modify
+dnl it under the terms of the GNU General Public License as published by
+dnl the Free Software Foundation; either version 2 of the License, or
+dnl (at your option) any later version.
+dnl
+dnl This program is distributed in the hope that it will be useful, but
+dnl WITHOUT ANY WARRANTY; without even the implied warranty of
+dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+dnl General Public License for more details.
+dnl
+dnl You should have received a copy of the GNU General Public License
+dnl along with this program; if not, write to the Free Software
+dnl Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+dnl 02111-1307, USA.
+dnl
+dnl As a special exception to the GNU General Public License, if you
+dnl distribute this file as part of a program that contains a
+dnl configuration script generated by Autoconf, you may include it under
+dnl the same distribution terms that you use for the rest of that
+dnl program.
+
+dnl PKG_PREREQ(MIN-VERSION)
+dnl -----------------------
+dnl Since: 0.29
+dnl
+dnl Verify that the version of the pkg-config macros are at least
+dnl MIN-VERSION. Unlike PKG_PROG_PKG_CONFIG, which checks the user's
+dnl installed version of pkg-config, this checks the developer's version
+dnl of pkg.m4 when generating configure.
+dnl
+dnl To ensure that this macro is defined, also add:
+dnl m4_ifndef([PKG_PREREQ],
+dnl     [m4_fatal([must install pkg-config 0.29 or later before running autoconf/autogen])])
+dnl
+dnl See the "Since" comment for each macro you use to see what version
+dnl of the macros you require.
+m4_defun([PKG_PREREQ],
+[m4_define([PKG_MACROS_VERSION], [0.29.1])
+m4_if(m4_version_compare(PKG_MACROS_VERSION, [$1]), -1,
+    [m4_fatal([pkg.m4 version $1 or higher is required but ]PKG_MACROS_VERSION[ found])])
+])dnl PKG_PREREQ
+
+dnl PKG_PROG_PKG_CONFIG([MIN-VERSION])
+dnl ----------------------------------
+dnl Since: 0.16
+dnl
+dnl Search for the pkg-config tool and set the PKG_CONFIG variable to
+dnl first found in the path. Checks that the version of pkg-config found
+dnl is at least MIN-VERSION. If MIN-VERSION is not specified, 0.9.0 is
+dnl used since that's the first version where most current features of
+dnl pkg-config existed.
+AC_DEFUN([PKG_PROG_PKG_CONFIG],
+[m4_pattern_forbid([^_?PKG_[A-Z_]+$])
+m4_pattern_allow([^PKG_CONFIG(_(PATH|LIBDIR|SYSROOT_DIR|ALLOW_SYSTEM_(CFLAGS|LIBS)))?$])
+m4_pattern_allow([^PKG_CONFIG_(DISABLE_UNINSTALLED|TOP_BUILD_DIR|DEBUG_SPEW)$])
+AC_ARG_VAR([PKG_CONFIG], [path to pkg-config utility])
+AC_ARG_VAR([PKG_CONFIG_PATH], [directories to add to pkg-config's search path])
+AC_ARG_VAR([PKG_CONFIG_LIBDIR], [path overriding pkg-config's built-in search path])
+
+if test "x$ac_cv_env_PKG_CONFIG_set" != "xset"; then
+	AC_PATH_TOOL([PKG_CONFIG], [pkg-config])
+fi
+if test -n "$PKG_CONFIG"; then
+	_pkg_min_version=m4_default([$1], [0.9.0])
+	AC_MSG_CHECKING([pkg-config is at least version $_pkg_min_version])
+	if $PKG_CONFIG --atleast-pkgconfig-version $_pkg_min_version; then
+		AC_MSG_RESULT([yes])
+	else
+		AC_MSG_RESULT([no])
+		PKG_CONFIG=""
+	fi
+fi[]dnl
+])dnl PKG_PROG_PKG_CONFIG
+
+dnl PKG_CHECK_EXISTS(MODULES, [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
+dnl -------------------------------------------------------------------
+dnl Since: 0.18
+dnl
+dnl Check to see whether a particular set of modules exists. Similar to
+dnl PKG_CHECK_MODULES(), but does not set variables or print errors.
+dnl
+dnl Please remember that m4 expands AC_REQUIRE([PKG_PROG_PKG_CONFIG])
+dnl only at the first occurence in configure.ac, so if the first place
+dnl it's called might be skipped (such as if it is within an "if", you
+dnl have to call PKG_CHECK_EXISTS manually
+AC_DEFUN([PKG_CHECK_EXISTS],
+[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
+if test -n "$PKG_CONFIG" && \
+    AC_RUN_LOG([$PKG_CONFIG --exists --print-errors "$1"]); then
+  m4_default([$2], [:])
+m4_ifvaln([$3], [else
+  $3])dnl
+fi])
+
+dnl _PKG_CONFIG([VARIABLE], [COMMAND], [MODULES])
+dnl ---------------------------------------------
+dnl Internal wrapper calling pkg-config via PKG_CONFIG and setting
+dnl pkg_failed based on the result.
+m4_define([_PKG_CONFIG],
+[if test -n "$$1"; then
+    pkg_cv_[]$1="$$1"
+ elif test -n "$PKG_CONFIG"; then
+    PKG_CHECK_EXISTS([$3],
+                     [pkg_cv_[]$1=`$PKG_CONFIG --[]$2 "$3" 2>/dev/null`
+		      test "x$?" != "x0" && pkg_failed=yes ],
+		     [pkg_failed=yes])
+ else
+    pkg_failed=untried
+fi[]dnl
+])dnl _PKG_CONFIG
+
+dnl _PKG_SHORT_ERRORS_SUPPORTED
+dnl ---------------------------
+dnl Internal check to see if pkg-config supports short errors.
+AC_DEFUN([_PKG_SHORT_ERRORS_SUPPORTED],
+[AC_REQUIRE([PKG_PROG_PKG_CONFIG])
+if $PKG_CONFIG --atleast-pkgconfig-version 0.20; then
+        _pkg_short_errors_supported=yes
+else
+        _pkg_short_errors_supported=no
+fi[]dnl
+])dnl _PKG_SHORT_ERRORS_SUPPORTED
+
+
+dnl PKG_CHECK_MODULES(VARIABLE-PREFIX, MODULES, [ACTION-IF-FOUND],
+dnl   [ACTION-IF-NOT-FOUND])
+dnl --------------------------------------------------------------
+dnl Since: 0.4.0
+dnl
+dnl Note that if there is a possibility the first call to
+dnl PKG_CHECK_MODULES might not happen, you should be sure to include an
+dnl explicit call to PKG_PROG_PKG_CONFIG in your configure.ac
+AC_DEFUN([PKG_CHECK_MODULES],
+[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
+AC_ARG_VAR([$1][_CFLAGS], [C compiler flags for $1, overriding pkg-config])dnl
+AC_ARG_VAR([$1][_LIBS], [linker flags for $1, overriding pkg-config])dnl
+
+pkg_failed=no
+AC_MSG_CHECKING([for $1])
+
+_PKG_CONFIG([$1][_CFLAGS], [cflags], [$2])
+_PKG_CONFIG([$1][_LIBS], [libs], [$2])
+
+m4_define([_PKG_TEXT], [Alternatively, you may set the environment variables $1[]_CFLAGS
+and $1[]_LIBS to avoid the need to call pkg-config.
+See the pkg-config man page for more details.])
+
+if test $pkg_failed = yes; then
+   	AC_MSG_RESULT([no])
+        _PKG_SHORT_ERRORS_SUPPORTED
+        if test $_pkg_short_errors_supported = yes; then
+	        $1[]_PKG_ERRORS=`$PKG_CONFIG --short-errors --print-errors --cflags --libs "$2" 2>&1`
+        else 
+	        $1[]_PKG_ERRORS=`$PKG_CONFIG --print-errors --cflags --libs "$2" 2>&1`
+        fi
+	# Put the nasty error message in config.log where it belongs
+	echo "$$1[]_PKG_ERRORS" >&AS_MESSAGE_LOG_FD
+
+	m4_default([$4], [AC_MSG_ERROR(
+[Package requirements ($2) were not met:
+
+$$1_PKG_ERRORS
+
+Consider adjusting the PKG_CONFIG_PATH environment variable if you
+installed software in a non-standard prefix.
+
+_PKG_TEXT])[]dnl
+        ])
+elif test $pkg_failed = untried; then
+     	AC_MSG_RESULT([no])
+	m4_default([$4], [AC_MSG_FAILURE(
+[The pkg-config script could not be found or is too old.  Make sure it
+is in your PATH or set the PKG_CONFIG environment variable to the full
+path to pkg-config.
+
+_PKG_TEXT
+
+To get pkg-config, see <http://pkg-config.freedesktop.org/>.])[]dnl
+        ])
+else
+	$1[]_CFLAGS=$pkg_cv_[]$1[]_CFLAGS
+	$1[]_LIBS=$pkg_cv_[]$1[]_LIBS
+        AC_MSG_RESULT([yes])
+	$3
+fi[]dnl
+])dnl PKG_CHECK_MODULES
+
+
+dnl PKG_CHECK_MODULES_STATIC(VARIABLE-PREFIX, MODULES, [ACTION-IF-FOUND],
+dnl   [ACTION-IF-NOT-FOUND])
+dnl ---------------------------------------------------------------------
+dnl Since: 0.29
+dnl
+dnl Checks for existence of MODULES and gathers its build flags with
+dnl static libraries enabled. Sets VARIABLE-PREFIX_CFLAGS from --cflags
+dnl and VARIABLE-PREFIX_LIBS from --libs.
+dnl
+dnl Note that if there is a possibility the first call to
+dnl PKG_CHECK_MODULES_STATIC might not happen, you should be sure to
+dnl include an explicit call to PKG_PROG_PKG_CONFIG in your
+dnl configure.ac.
+AC_DEFUN([PKG_CHECK_MODULES_STATIC],
+[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
+_save_PKG_CONFIG=$PKG_CONFIG
+PKG_CONFIG="$PKG_CONFIG --static"
+PKG_CHECK_MODULES($@)
+PKG_CONFIG=$_save_PKG_CONFIG[]dnl
+])dnl PKG_CHECK_MODULES_STATIC
+
+
+dnl PKG_INSTALLDIR([DIRECTORY])
+dnl -------------------------
+dnl Since: 0.27
+dnl
+dnl Substitutes the variable pkgconfigdir as the location where a module
+dnl should install pkg-config .pc files. By default the directory is
+dnl $libdir/pkgconfig, but the default can be changed by passing
+dnl DIRECTORY. The user can override through the --with-pkgconfigdir
+dnl parameter.
+AC_DEFUN([PKG_INSTALLDIR],
+[m4_pushdef([pkg_default], [m4_default([$1], ['${libdir}/pkgconfig'])])
+m4_pushdef([pkg_description],
+    [pkg-config installation directory @<:@]pkg_default[@:>@])
+AC_ARG_WITH([pkgconfigdir],
+    [AS_HELP_STRING([--with-pkgconfigdir], pkg_description)],,
+    [with_pkgconfigdir=]pkg_default)
+AC_SUBST([pkgconfigdir], [$with_pkgconfigdir])
+m4_popdef([pkg_default])
+m4_popdef([pkg_description])
+])dnl PKG_INSTALLDIR
+
+
+dnl PKG_NOARCH_INSTALLDIR([DIRECTORY])
+dnl --------------------------------
+dnl Since: 0.27
+dnl
+dnl Substitutes the variable noarch_pkgconfigdir as the location where a
+dnl module should install arch-independent pkg-config .pc files. By
+dnl default the directory is $datadir/pkgconfig, but the default can be
+dnl changed by passing DIRECTORY. The user can override through the
+dnl --with-noarch-pkgconfigdir parameter.
+AC_DEFUN([PKG_NOARCH_INSTALLDIR],
+[m4_pushdef([pkg_default], [m4_default([$1], ['${datadir}/pkgconfig'])])
+m4_pushdef([pkg_description],
+    [pkg-config arch-independent installation directory @<:@]pkg_default[@:>@])
+AC_ARG_WITH([noarch-pkgconfigdir],
+    [AS_HELP_STRING([--with-noarch-pkgconfigdir], pkg_description)],,
+    [with_noarch_pkgconfigdir=]pkg_default)
+AC_SUBST([noarch_pkgconfigdir], [$with_noarch_pkgconfigdir])
+m4_popdef([pkg_default])
+m4_popdef([pkg_description])
+])dnl PKG_NOARCH_INSTALLDIR
+
+
+dnl PKG_CHECK_VAR(VARIABLE, MODULE, CONFIG-VARIABLE,
+dnl [ACTION-IF-FOUND], [ACTION-IF-NOT-FOUND])
+dnl -------------------------------------------
+dnl Since: 0.28
+dnl
+dnl Retrieves the value of the pkg-config variable for the given module.
+AC_DEFUN([PKG_CHECK_VAR],
+[AC_REQUIRE([PKG_PROG_PKG_CONFIG])dnl
+AC_ARG_VAR([$1], [value of $3 for $2, overriding pkg-config])dnl
+
+_PKG_CONFIG([$1], [variable="][$3]["], [$2])
+AS_VAR_COPY([$1], [pkg_cv_][$1])
+
+AS_VAR_IF([$1], [""], [$5], [$4])dnl
+])dnl PKG_CHECK_VAR
+
+dnl PKG_WITH_MODULES(VARIABLE-PREFIX, MODULES,
+dnl   [ACTION-IF-FOUND],[ACTION-IF-NOT-FOUND],
+dnl   [DESCRIPTION], [DEFAULT])
+dnl ------------------------------------------
+dnl
+dnl Prepare a "--with-" configure option using the lowercase
+dnl [VARIABLE-PREFIX] name, merging the behaviour of AC_ARG_WITH and
+dnl PKG_CHECK_MODULES in a single macro.
+AC_DEFUN([PKG_WITH_MODULES],
+[
+m4_pushdef([with_arg], m4_tolower([$1]))
+
+m4_pushdef([description],
+           [m4_default([$5], [build with ]with_arg[ support])])
+
+m4_pushdef([def_arg], [m4_default([$6], [auto])])
+m4_pushdef([def_action_if_found], [AS_TR_SH([with_]with_arg)=yes])
+m4_pushdef([def_action_if_not_found], [AS_TR_SH([with_]with_arg)=no])
+
+m4_case(def_arg,
+            [yes],[m4_pushdef([with_without], [--without-]with_arg)],
+            [m4_pushdef([with_without],[--with-]with_arg)])
+
+AC_ARG_WITH(with_arg,
+     AS_HELP_STRING(with_without, description[ @<:@default=]def_arg[@:>@]),,
+    [AS_TR_SH([with_]with_arg)=def_arg])
+
+AS_CASE([$AS_TR_SH([with_]with_arg)],
+            [yes],[PKG_CHECK_MODULES([$1],[$2],$3,$4)],
+            [auto],[PKG_CHECK_MODULES([$1],[$2],
+                                        [m4_n([def_action_if_found]) $3],
+                                        [m4_n([def_action_if_not_found]) $4])])
+
+m4_popdef([with_arg])
+m4_popdef([description])
+m4_popdef([def_arg])
+
+])dnl PKG_WITH_MODULES
+
+dnl PKG_HAVE_WITH_MODULES(VARIABLE-PREFIX, MODULES,
+dnl   [DESCRIPTION], [DEFAULT])
+dnl -----------------------------------------------
+dnl
+dnl Convenience macro to trigger AM_CONDITIONAL after PKG_WITH_MODULES
+dnl check._[VARIABLE-PREFIX] is exported as make variable.
+AC_DEFUN([PKG_HAVE_WITH_MODULES],
+[
+PKG_WITH_MODULES([$1],[$2],,,[$3],[$4])
+
+AM_CONDITIONAL([HAVE_][$1],
+               [test "$AS_TR_SH([with_]m4_tolower([$1]))" = "yes"])
+])dnl PKG_HAVE_WITH_MODULES
+
+dnl PKG_HAVE_DEFINE_WITH_MODULES(VARIABLE-PREFIX, MODULES,
+dnl   [DESCRIPTION], [DEFAULT])
+dnl ------------------------------------------------------
+dnl
+dnl Convenience macro to run AM_CONDITIONAL and AC_DEFINE after
+dnl PKG_WITH_MODULES check. HAVE_[VARIABLE-PREFIX] is exported as make
+dnl and preprocessor variable.
+AC_DEFUN([PKG_HAVE_DEFINE_WITH_MODULES],
+[
+PKG_HAVE_WITH_MODULES([$1],[$2],[$3],[$4])
+
+AS_IF([test "$AS_TR_SH([with_]m4_tolower([$1]))" = "yes"],
+        [AC_DEFINE([HAVE_][$1], 1, [Enable ]m4_tolower([$1])[ support])])
+])dnl PKG_HAVE_DEFINE_WITH_MODULES
diff --git a/src/musl-libgen-c.h b/src/musl-libgen-c.h
index 99c90ee..d947197 100644
--- a/src/musl-libgen-c.h
+++ b/src/musl-libgen-c.h
@@ -1,4 +1,5 @@
-/*
+/* SPDX-License-Identifier: MIT
+ *
  * Copied from musl.
  *
  * Copyright © 2005-2014 Rich Felker, et al.
diff --git a/src/random-seed.c b/src/random-seed.c
index 0b7c5c4..b8e8ad7 100644
--- a/src/random-seed.c
+++ b/src/random-seed.c
@@ -1,17 +1,4 @@
-/* Copyright 2018 Alex Xu (aka Hello71, alxu)
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
+// SPDX-License-Identifier: BSD-3-Clause
 
 #include <assert.h>
 #include <errno.h>
@@ -30,6 +17,7 @@
 #include <sys/syscall.h>
 #include <unistd.h>
 
+#include "config.h"
 #include "musl-libgen-c.h"
 #include "util.h"
 
diff --git a/src/sha2.c b/src/sha2.c
index 4c2b615..d949537 100644
--- a/src/sha2.c
+++ b/src/sha2.c
@@ -1,4 +1,5 @@
-/*
+/* SPDX-License-Identifier: BSD-3-Clause
+ *
  * FIPS 180-2 SHA-224/256/384/512 implementation
  * Last update: 02/02/2007
  * Issue date:  04/30/2005
diff --git a/src/sha2.h b/src/sha2.h
index bd968ba..e55b74f 100644
--- a/src/sha2.h
+++ b/src/sha2.h
@@ -1,4 +1,5 @@
-/*
+/* SPDX-License-Identifier: BSD-3-Clause
+ *
  * FIPS 180-2 SHA-224/256/384/512 implementation
  * Last update: 02/02/2007
  * Issue date:  04/30/2005
diff --git a/src/util.c b/src/util.c
index a5eb220..908e3a2 100644
--- a/src/util.c
+++ b/src/util.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: BSD-3-Clause
+
 #include <assert.h>
 #include <limits.h>
 #include <stddef.h>
diff --git a/src/util.h b/src/util.h
index 9cd2bd4..8759cd0 100644
--- a/src/util.h
+++ b/src/util.h
@@ -1,5 +1,7 @@
-#ifndef UTIL_H
-#define UTIL_H
+// SPDX-License-Identifier: BSD-3-Clause
+
+#ifndef RANDOM_SEED_UTIL_H
+#define RANDOM_SEED_UTIL_H
 
 #include <errno.h>
 #include <stdbool.h>
diff --git a/random-seed-save.service.in b/systemd/random-seed-save.service.in
index e70192b..e70192b 100644
--- a/random-seed-save.service.in
+++ b/systemd/random-seed-save.service.in
diff --git a/random-seed-save.timer b/systemd/random-seed-save.timer
index f39227d..f39227d 100644
--- a/random-seed-save.timer
+++ b/systemd/random-seed-save.timer
diff --git a/random-seed.service.in b/systemd/random-seed.service.in
index 97bda54..97bda54 100644
--- a/random-seed.service.in
+++ b/systemd/random-seed.service.in