[PATCH liburing v3 2/4] src/Makefile: Add header files as dependency

[Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>]

When the header files are modified, the compiled objects are not going
to be recompiled because the header files are not marked as a dependency
for the objects.

  - Instruct the compiler to generate dependency files.

  - Include those files from src/Makefile. Ensure if any changes are
    made, files that depend on the changes are recompiled.

Suggested-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
---

v2 -> v3: 
  - Add dependency files to .gitignore.
  - Remove dependency files when running "make clean".

 .gitignore   |  1 +
 src/Makefile | 13 ++++++-------
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/.gitignore b/.gitignore
index c9dc77f..9b74880 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,6 +3,7 @@
 *~
 /*.patch
 
+*.d
 *.o
 *.o[ls]
 
diff --git a/src/Makefile b/src/Makefile
index f19d45e..0e04986 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -43,19 +43,20 @@ else
 	liburing_srcs += syscall.c
 endif
 
+override CPPFLAGS += -MT "$@" -MMD -MP -MF "$@.d"
 liburing_objs := $(patsubst %.c,%.ol,$(liburing_srcs))
 liburing_sobjs := $(patsubst %.c,%.os,$(liburing_srcs))
 
-$(liburing_srcs): syscall.h lib.h
-
-$(liburing_objs) $(liburing_sobjs): include/liburing/io_uring.h
-
 %.os: %.c
 	$(QUIET_CC)$(CC) $(CPPFLAGS) $(SO_CFLAGS) -c -o $@ $<
 
 %.ol: %.c
 	$(QUIET_CC)$(CC) $(CPPFLAGS) $(L_CFLAGS) -c -o $@ $<
 
+# Include compiler generated dependency files.
+-include $(liburing_objs:%=%.d)
+-include $(liburing_sobjs:%=%.d)
+
 AR ?= ar
 RANLIB ?= ranlib
 liburing.a: $(liburing_objs)
@@ -78,11 +79,9 @@ ifeq ($(ENABLE_SHARED),1)
 	ln -sf $(relativelibdir)$(libname) $(libdevdir)/liburing.so
 endif
 
-$(liburing_objs): include/liburing.h
-
 clean:
 	@rm -f $(all_targets) $(liburing_objs) $(liburing_sobjs) $(soname).new
-	@rm -f *.so* *.a *.o
+	@rm -f *.so* *.a *.o *.d
 	@rm -f include/liburing/compat.h
 
 	@# When cleaning, we don't include ../config-host.mak,
-- 
2.25.1