From: Jeff Mahoney <jeffm@suse.com>
Subject: btrfsprogs: only install udev rules for udev >= 190
Patch-mainline: Submitted, linux-btrfs 30 Aug 2016

Prior to udev v190, there was no btrfs builtin helper.  Installing it on
systems with an older udev will cause problems.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---

 configure.ac |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 97e89f2..8fd8f42 100644
--- a/configure.ac
+++ b/configure.ac
@@ -161,7 +161,13 @@ PKG_STATIC(UUID_LIBS_STATIC, [uuid])
 PKG_CHECK_MODULES(ZLIB, [zlib])
 PKG_STATIC(ZLIB_LIBS_STATIC, [zlib])
 
-UDEVDIR="$(pkg-config udev --variable=udevdir)"
+# udev v190 introduced the btrfs builtin and a udev rule to use it.
+# Our udev rule gives us the friendly dm names but isn't required (or valid)
+# on earlier releases.
+UDEVDIR=
+if pkg-config udev --atleast-version 190; then
+	UDEVDIR="$(pkg-config udev --variable=udevdir)"
+fi
 AC_SUBST(UDEVDIR)
 
 dnl lzo library does not provide pkg-config, let use classic way