btrfs-progs: build: add optional dependency on libudev

This is needed for future code which will make btrfs-progs' device
scanning logic a little smarter by filtering out path device in
multipath setups. libudev is added as an optional dependency since the
library doesn't have a static version so making it a hard dependency
means forfeiting static build support. To alleviate this a fallback code
will be added for the static build case which doesn't rely on libudev.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Makefile

@@ -129,7 +129,7 @@ LIBS = $(LIBS_BASE) $(LIBS_CRYPTO)
 LIBBTRFS_LIBS = $(LIBS_BASE) $(LIBS_CRYPTO)
 
 # Static compilation flags
-STATIC_CFLAGS = $(CFLAGS) -ffunction-sections -fdata-sections
+STATIC_CFLAGS = $(CFLAGS) -ffunction-sections -fdata-sections -DSTATIC_BUILD
 STATIC_LDFLAGS = -static -Wl,--gc-sections
 STATIC_LIBS = $(STATIC_LIBS_BASE)
 

Makefile.inc.in

@@ -27,7 +27,7 @@ CRYPTO_CFLAGS = @GCRYPT_CFLAGS@ @SODIUM_CFLAGS@ @KCAPI_CFLAGS@
 SUBST_CFLAGS = @CFLAGS@
 SUBST_LDFLAGS = @LDFLAGS@
 
-LIBS_BASE = @UUID_LIBS@ @BLKID_LIBS@ -L. -pthread
+LIBS_BASE = @UUID_LIBS@ @BLKID_LIBS@ @LIBUDEV_LIBS@ -L. -pthread
 LIBS_COMP = @ZLIB_LIBS@ @LZO2_LIBS@ @ZSTD_LIBS@
 LIBS_PYTHON = @PYTHON_LIBS@
 LIBS_CRYPTO = @GCRYPT_LIBS@ @SODIUM_LIBS@ @KCAPI_LIBS@

configure.ac

@@ -317,6 +317,15 @@ fi
 AS_IF([test "x$enable_zstd" = xyes], [BTRFSRESTORE_ZSTD=1], [BTRFSRESTORE_ZSTD=0])
 AC_SUBST(BTRFSRESTORE_ZSTD)
 
+PKG_CHECK_EXISTS([libudev], [pkg_config_libudev=yes], [pkg_config_libudev=no])
+if test "x$pkg_config_libudev" = xyes; then
+	PKG_CHECK_MODULES([LIBUDEV], [libudev])
+	AC_DEFINE([HAVE_LIBUDEV], [1], [Define to 1 if libudev is available])
+else
+	AC_MSG_CHECKING([for LIBUDEV])
+	AC_MSG_RESULT([no])
+fi
+
 AC_ARG_ENABLE([python],
 	AS_HELP_STRING([--disable-python], [do not build libbtrfsutil Python bindings]),
 	[], [enable_python=$enable_shared]