Re: [PATCH bpf-next v2 6/9] bpf: iterators: install libbpf headers when building

On Mon, 4 Oct 2021 at 20:11, Andrii Nakryiko [off-list ref] wrote:

On Sat, Oct 2, 2021 at 3:12 PM Quentin Monnet [off-list ref] wrote:

quoted

On Sat, 2 Oct 2021 at 21:27, Quentin Monnet [off-list ref] wrote:

quoted

On Sat, 2 Oct 2021 at 00:20, Andrii Nakryiko [off-list ref] wrote:

quoted

On Fri, Oct 1, 2021 at 4:09 AM Quentin Monnet [off-list ref] wrote:

quoted

API headers from libbpf should not be accessed directly from the
library's source directory. Instead, they should be exported with "make
install_headers". Let's make sure that bpf/preload/iterators/Makefile
installs the headers properly when building.

quoted

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-$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(OUTPUT)
+$(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile)            \
+          | $(LIBBPF_OUTPUT) $(LIBBPF_INCLUDE)

Would it make sense for libbpf's Makefile to create include and output
directories on its own? We wouldn't need to have these order-only
dependencies everywhere, right?

Good point, I'll have a look at it.
Quentin

So libbpf already creates the include (and parent $(DESTDIR))
directory, so I can get rid of the related dependencies. But I don't
see an easy solution for the output directory for the object files.
The issue is that libbpf's Makefile includes
tools/scripts/Makefile.include, which checks $(OUTPUT) and errors out

Did you check what benefits the use of tools/scripts/Makefile.include
brings? Last time I had to deal with some non-trivial Makefile
problem, this extra dance with tools/scripts/Makefile.include and some
related complexities didn't seem very justified. So unless there are
some very big benefits to having tool's Makefile.include included, I'd
rather simplify libbpf's in-kernel Makefile and make it more
straightforward. We have a completely independent separate Makefile
for libbpf in Github, and I think it's more straightforward. Doesn't
have to be done in this change, of course, but I was curious to hear
your thoughts given you seem to have spent tons of time on this
already.

No, I haven't checked in details so far. I remember that several
elements defined in the Makefile.include are used in libbpf's
Makefile, and I stopped at that, because I thought that a refactoring
of the latter would be beyond the current set. But yes, I can have a
look at it and see if it's worth changing in a follow-up.