cgroup: selftests: Move cgroup_util into its own library

KVM selftests will soon need to use some of the cgroup creation and
deletion functionality from cgroup_util.

Suggested-by: David Matlack <[e-mail]>
Signed-off-by: James Houghton <[e-mail]>
Acked-by: Tejun Heo <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Sean Christopherson <[e-mail]>

tools/testing/selftests/cgroup/Makefile

···
 LOCAL_HDRS += $(selfdir)/clone3/clone3_selftests.h $(selfdir)/pidfd/pidfd.h
 
 include ../lib.mk
+include lib/libcgroup.mk
 
-$(OUTPUT)/test_core: cgroup_util.c
-$(OUTPUT)/test_cpu: cgroup_util.c
-$(OUTPUT)/test_cpuset: cgroup_util.c
-$(OUTPUT)/test_freezer: cgroup_util.c
-$(OUTPUT)/test_hugetlb_memcg: cgroup_util.c
-$(OUTPUT)/test_kill: cgroup_util.c
-$(OUTPUT)/test_kmem: cgroup_util.c
-$(OUTPUT)/test_memcontrol: cgroup_util.c
-$(OUTPUT)/test_pids: cgroup_util.c
-$(OUTPUT)/test_zswap: cgroup_util.c
+$(OUTPUT)/test_core: $(LIBCGROUP_O)
+$(OUTPUT)/test_cpu: $(LIBCGROUP_O)
+$(OUTPUT)/test_cpuset: $(LIBCGROUP_O)
+$(OUTPUT)/test_freezer: $(LIBCGROUP_O)
+$(OUTPUT)/test_hugetlb_memcg: $(LIBCGROUP_O)
+$(OUTPUT)/test_kill: $(LIBCGROUP_O)
+$(OUTPUT)/test_kmem: $(LIBCGROUP_O)
+$(OUTPUT)/test_memcontrol: $(LIBCGROUP_O)
+$(OUTPUT)/test_pids: $(LIBCGROUP_O)
+$(OUTPUT)/test_zswap: $(LIBCGROUP_O)

tools/testing/selftests/cgroup/cgroup_util.c tools/testing/selftests/cgroup/lib/cgroup_util.c

···
 #include <unistd.h>
 
 #include "cgroup_util.h"
-#include "../clone3/clone3_selftests.h"
+#include "../../clone3/clone3_selftests.h"
 
 /* Returns read len on success, or -errno on failure. */
 ssize_t read_text(const char *path, char *buf, size_t max_len)

tools/testing/selftests/cgroup/cgroup_util.h tools/testing/selftests/cgroup/lib/include/cgroup_util.h

···
 #include <stdbool.h>
 #include <stdlib.h>
 
-#include "../kselftest.h"
-
+#ifndef PAGE_SIZE
 #define PAGE_SIZE 4096
+#endif
 
 #define MB(x) (x << 20)
 

tools/testing/selftests/cgroup/lib/libcgroup.mk

···
+CGROUP_DIR := $(selfdir)/cgroup
+
+LIBCGROUP_C := lib/cgroup_util.c
+
+LIBCGROUP_O := $(patsubst %.c, $(OUTPUT)/%.o, $(LIBCGROUP_C))
+
+LIBCGROUP_O_DIRS := $(shell dirname $(LIBCGROUP_O) | uniq)
+
+CFLAGS += -I$(CGROUP_DIR)/lib/include
+
+EXTRA_HDRS := $(selfdir)/clone3/clone3_selftests.h
+
+$(LIBCGROUP_O_DIRS):
+	mkdir -p $@
+
+$(LIBCGROUP_O): $(OUTPUT)/%.o : $(CGROUP_DIR)/%.c $(EXTRA_HDRS) $(LIBCGROUP_O_DIRS)
+	$(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c $< -o $@
+
+EXTRA_CLEAN += $(LIBCGROUP_O)