[PATCH v3] libtracefs: Add trace.conf for ld.so if needed

[Steven Rostedt <rostedt@goodmis.org>]

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

It cannot be guaranteed that the system the library is being installed on
has ld.so set to search the location of where libtracefs.so is installed.

During the install process, check if the path is found in ld.so.conf.d/ and
if not, test if an executable can be built and find the library. If it can
not, then add the path to ld.so.conf.d/trace.conf, and run ldconfig again.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
  Changes since v2:
    - Quiet errors in compiling or running test program in install.
      Add print of installing trace.conf if needed.

 Makefile | 27 +++++++++++++++++++++++++++
 test.c   |  7 +++++++
 2 files changed, 34 insertions(+)
 create mode 100644 test.c

diff --git a/Makefile b/Makefile
index b4d0a72..5e78314 100644
--- a/Makefile
+++ b/Makefile
@@ -28,6 +28,8 @@ endef
 $(call allow-override,CC,$(CROSS_COMPILE)gcc)
 $(call allow-override,AR,$(CROSS_COMPILE)ar)
 $(call allow-override,PKG_CONFIG,pkg-config)
+$(call allow-override,LD_SO_CONF_PATH,/etc/ld.so.conf.d/)
+$(call allow-override,LDCONFIG,ldconfig)
 
 EXT = -std=gnu99
 INSTALL = install
@@ -235,11 +237,36 @@ cscope: force
 	$(RM) cscope*
 	$(call find_tag_files) | cscope -b -q
 
+ifeq ("$(DESTDIR)", "")
+# If DESTDIR is not defined, then test if after installing the library
+# and running ldconfig, if the library is visible by ld.so.
+# If not, add the path to /etc/ld.so.conf.d/trace.conf and run ldconfig again.
+define install_ld_config
+	$(LDCONFIG); \
+	if ! grep "^$(libdir)$$" $(LD_SO_CONF_PATH)/* &> /dev/null ; then \
+		$(CC) -o $(OUTPUT)test $(srctree)/test.c -I $(includedir_SQ) \
+			-L $(libdir_SQ) -ltracefs &> /dev/null; \
+		if ! $(OUTPUT)test &> /dev/null; then \
+			$(call print_install, trace.conf, $(LD_SO_CONF_PATH)) \
+			echo $(libdir_SQ) >> $(LD_SO_CONF_PATH)/trace.conf; \
+			$(LDCONFIG); \
+		fi; \
+		$(RM) $(OUTPUT)test; \
+	fi
+endef
+else
+# If installing to a location for another machine or package, do not bother
+# with running ldconfig.
+define install_ld_config
+endef
+endif # DESTDIR = ""
+
 install_libs: libs install_pkgconfig
 	$(Q)$(call do_install,$(LIBTRACEFS_SHARED),$(libdir_SQ)); \
 		cp -fpR $(LIB_INSTALL) $(DESTDIR)$(libdir_SQ)
 	$(Q)$(call do_install,$(src)/include/tracefs.h,$(includedir_SQ))
 	$(Q)$(call do_install_ld,$(TRACE_LD_FILE),$(LD_SO_CONF_DIR),$(libdir_SQ))
+	$(Q)$(call install_ld_config)
 
 install: install_libs
 
diff --git a/test.c b/test.c
new file mode 100644
index 0000000..daf99d6
--- /dev/null
+++ b/test.c
@@ -0,0 +1,7 @@
+#include <tracefs.h>
+
+int main()
+{
+	tracefs_get_tracing_dir();
+	return 0;
+}
-- 
2.25.4