Re: [PATCH v2 3/5] cgroup: selftests: Move cgroup_util into its own library

[David Matlack]

On Mon, Mar 31, 2025 at 2:30 PM James Houghton <jthoughton@xxxxxxxxxx> wrote:
>
> KVM selftests will soon need to use some of the cgroup creation and
> deletion functionality from cgroup_util.
>
> Suggested-by: David Matlack <dmatlack@xxxxxxxxxx>
> Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
> ---
>  tools/testing/selftests/cgroup/Makefile       | 21 ++++++++++---------
>  .../selftests/cgroup/{ => lib}/cgroup_util.c  |  2 +-
>  .../cgroup/{ => lib/include}/cgroup_util.h    |  4 ++--
>  .../testing/selftests/cgroup/lib/libcgroup.mk | 14 +++++++++++++
>  4 files changed, 28 insertions(+), 13 deletions(-)
>  rename tools/testing/selftests/cgroup/{ => lib}/cgroup_util.c (99%)
>  rename tools/testing/selftests/cgroup/{ => lib/include}/cgroup_util.h (99%)
>  create mode 100644 tools/testing/selftests/cgroup/lib/libcgroup.mk
>
> diff --git a/tools/testing/selftests/cgroup/Makefile b/tools/testing/selftests/cgroup/Makefile
> index 1b897152bab6e..e01584c2189ac 100644
> --- a/tools/testing/selftests/cgroup/Makefile
> +++ b/tools/testing/selftests/cgroup/Makefile
> @@ -21,14 +21,15 @@ TEST_GEN_PROGS += test_zswap
>  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)
> diff --git a/tools/testing/selftests/cgroup/cgroup_util.c b/tools/testing/selftests/cgroup/lib/cgroup_util.c
> similarity index 99%
> rename from tools/testing/selftests/cgroup/cgroup_util.c
> rename to tools/testing/selftests/cgroup/lib/cgroup_util.c
> index 1e2d46636a0ca..f047d8adaec65 100644
> --- a/tools/testing/selftests/cgroup/cgroup_util.c
> +++ b/tools/testing/selftests/cgroup/lib/cgroup_util.c
> @@ -17,7 +17,7 @@
>  #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. */
>  static ssize_t read_text(const char *path, char *buf, size_t max_len)
> diff --git a/tools/testing/selftests/cgroup/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
> similarity index 99%
> rename from tools/testing/selftests/cgroup/cgroup_util.h
> rename to tools/testing/selftests/cgroup/lib/include/cgroup_util.h
> index 19b131ee77072..7a0441e5eb296 100644
> --- a/tools/testing/selftests/cgroup/cgroup_util.h
> +++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h
> @@ -2,9 +2,9 @@
>  #include <stdbool.h>
>  #include <stdlib.h>
>
> -#include "../kselftest.h"
> -
> +#ifndef PAGE_SIZE
>  #define PAGE_SIZE 4096
> +#endif
>
>  #define MB(x) (x << 20)
>
> diff --git a/tools/testing/selftests/cgroup/lib/libcgroup.mk b/tools/testing/selftests/cgroup/lib/libcgroup.mk
> new file mode 100644
> index 0000000000000..12323041a5ce6
> --- /dev/null
> +++ b/tools/testing/selftests/cgroup/lib/libcgroup.mk
> @@ -0,0 +1,14 @@
> +CGROUP_DIR := $(selfdir)/cgroup
> +
> +LIBCGROUP_C := lib/cgroup_util.c
> +
> +LIBCGROUP_O := $(patsubst %.c, $(OUTPUT)/%.o, $(LIBCGROUP_C))
> +
> +CFLAGS += -I$(CGROUP_DIR)/lib/include
> +
> +EXTRA_HDRS := $(selfdir)/clone3/clone3_selftests.h
> +
> +$(LIBCGROUP_O): $(OUTPUT)/%.o : $(CGROUP_DIR)/%.c $(EXTRA_HDRS)
> +       $(CC) $(CFLAGS) $(CPPFLAGS) $(TARGET_ARCH) -c $< -o $@
> +
> +EXTRA_CLEAN += $(LIBCGROUP_O)
> --
> 2.49.0.472.ge94155a9ec-goog

This works since KVM selftests already have a lib/ directory. But if
it didn't, the KVM selftests would fail to link against
lib/cgroup_util.o. To future proof against using this from other
selftests (or if someone were to add a subdirectory to
selftests/cgroup/lib), you can add a rule to create any missing
directories in the $(OUTPUT) path:

LIBCGROUP_O_DIRS := $(shell dirname $(LIBCGROUP_O) | uniq)

$(LIBCGROUP_O_DIRS):
        mkdir -p $@

Then add $(LIBCGROUP_O_DIRS) as a dependency of $(LIBCGROUP_O).