netdev - Re: [PATCH bpf-next] tools/bpf: generate pkg-config file for libbpf

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Message-ID: <20190319212303.GE7431@mini-arch.hsd1.ca.comcast.net>
Date:   Tue, 19 Mar 2019 14:23:03 -0700
From:   Stanislav Fomichev <sdf@...ichev.me>
To:     Luca Boccassi <bluca@...ian.org>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next] tools/bpf: generate pkg-config file for libbpf

On 03/19, Luca Boccassi wrote:
> Generate a libbpf.pc file at build time so that users can rely
> on pkg-config to find the library, its CFLAGS and LDFLAGS.
> 
> Signed-off-by: Luca Boccassi <bluca@...ian.org>
> ---
>  tools/lib/bpf/.gitignore         |  1 +
>  tools/lib/bpf/Makefile           | 18 +++++++++++++++---
>  tools/lib/bpf/libbpf.pc.template | 11 +++++++++++
>  3 files changed, 27 insertions(+), 3 deletions(-)
>  create mode 100644 tools/lib/bpf/libbpf.pc.template
> 
> diff --git a/tools/lib/bpf/.gitignore b/tools/lib/bpf/.gitignore
> index 4db74758c674..7d9e182a1f51 100644
> --- a/tools/lib/bpf/.gitignore
> +++ b/tools/lib/bpf/.gitignore
> @@ -1,3 +1,4 @@
>  libbpf_version.h
> +libbpf.pc
>  FEATURE-DUMP.libbpf
>  test_libbpf
> diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
> index a05c43468bd0..542c64e2a6d9 100644
> --- a/tools/lib/bpf/Makefile
> +++ b/tools/lib/bpf/Makefile
> @@ -80,6 +80,7 @@ libdir_SQ = $(subst ','\'',$(libdir))
>  libdir_relative_SQ = $(subst ','\'',$(libdir_relative))
>  
>  LIB_FILE = libbpf.a libbpf.so
> +PC_FILE = libbpf.pc
>  
>  VERSION		= $(BPF_VERSION)
>  PATCHLEVEL	= $(BPF_PATCHLEVEL)
> @@ -137,7 +138,7 @@ GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN) | \
>  VERSIONED_SYM_COUNT = $(shell readelf -s --wide $(OUTPUT)libbpf.so | \
>  			      grep -Eo '[^ ]+@...BPF_' | cut -d@ -f1 | sort -u | wc -l)
>  
> -CMD_TARGETS = $(LIB_FILE)
> +CMD_TARGETS = $(LIB_FILE) $(PC_FILE)
>  
>  CXX_TEST_TARGET = $(OUTPUT)test_libbpf
>  
> @@ -179,6 +180,12 @@ $(OUTPUT)libbpf.a: $(BPF_IN)
>  $(OUTPUT)test_libbpf: test_libbpf.cpp $(OUTPUT)libbpf.a
>  	$(QUIET_LINK)$(CXX) $(INCLUDES) $^ -lelf -o $@
>  
> +$(OUTPUT)libbpf.pc:
> +	$(QUIET_LINK)sed -e "s|@...FIX@|$(prefix)|" \
Maybe QUIET_GEN instead? Or QUIET_INSTALL (tools/lib/traceevent/Makefile)?

> +		-e "s|@...DIR@|$(libdir_SQ)|" \
> +		-e "s|@...SION@|$(shell make --no-print-directory -sC ../../.. kernelversion)|" \
Make it its own variable, like we do in bpftool?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/bpf/bpftool/Makefile#n26

Also, I wonder what would happen in the case of out-of-tree libbpf:
https://github.com/libbpf/libbpf

Should there be some fallback?

> +		< $@...mplate > $@
> +
>  check: check_abi
>  
>  check_abi: $(OUTPUT)libbpf.so
> @@ -208,7 +215,12 @@ install_headers:
>  		$(call do_install,libbpf.h,$(prefix)/include/bpf,644);
>  		$(call do_install,btf.h,$(prefix)/include/bpf,644);
>  
> -install: install_lib
> +install_pkgconfig: $(PC_FILE)
> +	$(call QUIET_INSTALL, $(PC_FILE)) \
> +		$(call do_install,$(PC_FILE),$(libdir_SQ)/pkgconfig,644)
> +
> +
> +install: install_lib install_pkgconfig
>  
>  ### Cleaning rules
>  
> @@ -218,7 +230,7 @@ config-clean:
>  
>  clean:
>  	$(call QUIET_CLEAN, libbpf) $(RM) $(TARGETS) $(CXX_TEST_TARGET) \
> -		*.o *~ *.a *.so .*.d .*.cmd LIBBPF-CFLAGS
> +		*.o *~ *.a *.so .*.d .*.cmd *.pc LIBBPF-CFLAGS
>  	$(call QUIET_CLEAN, core-gen) $(RM) $(OUTPUT)FEATURE-DUMP.libbpf
>  
>  
> diff --git a/tools/lib/bpf/libbpf.pc.template b/tools/lib/bpf/libbpf.pc.template
> new file mode 100644
> index 000000000000..0cac2f5f54a6
> --- /dev/null
> +++ b/tools/lib/bpf/libbpf.pc.template
> @@ -0,0 +1,11 @@
> +prefix=@...FIX@
> +libdir=@...DIR@
> +includedir=${prefix}/include/bpf
> +
> +Name: libbpf
> +URL: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
> +Description: Linux kernel BPF library
> +Version: @VERSION@
> +Libs: -L${libdir} -lbpf
> +Requires.private: libelf
> +Cflags: -I${includedir}
> -- 
> 2.20.1
>