netdev - Re: [PATCH bpf-next v4 09/10] selftests: Remove tools/lib/bpf from include path

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Date:   Mon, 20 Jan 2020 12:06:44 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        John Fastabend <john.fastabend@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-rdma@...r.kernel.org,
        "open list\:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH bpf-next v4 09/10] selftests: Remove tools/lib/bpf from include path

[...]
> I really-really didn't like this alternating dependency on directory
> or a set of file, depending on current state of those temporary
> directories. Then also this ugly check to avoid circular dependency.
> All that seemed wrong. So I played a bit with how to achieve the same
> differently, and here's what I came up with, which I like a bit
> better. What do you think?
>
> $(BPFOBJ): $(wildcard $(BPFDIR)/*.c $(BPFDIR)/*.h $(BPFDIR)/Makefile)          \
>            ../../../include/uapi/linux/bpf.h                                   \
>            | $(INCLUDE_DIR) $(BUILD_DIR)/libbpf
>         $(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
>                     DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
>
> So, essentially, just make sure that we install local copies of
> headers whenever libbpf.a needs to be re-built.
> ../../../include/uapi/linux/bpf.h ensures we don't miss uapi header
> changes as well. Now anything that uses libbpf headers will need to
> depend on $(BPFOBJ) and will automatically get up-to-date local copies
> of headers.
>
> This seems much simpler. Please give it a try, thanks!

Yes, this is a good idea! It did actually occur to me that the $(BPFOBJ)
rule could just include the install_headers make arg, but only after I
sent out this latest version. Thank you for taking the time to work out
the details, I'll fold this in :)

-Toke