linux-kernel - Re: [PATCH] bpfilter: remove extra header search paths for bpfilter

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Date:   Sat, 2 Feb 2019 22:40:37 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>,
        Matteo Croce <mcroce@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Laura Abbott <labbott@...hat.com>,
        YueHaibing <yuehaibing@...wei.com>
Subject: Re: [PATCH] bpfilter: remove extra header search paths for bpfilter_umh

On Sat, Feb 2, 2019 at 9:00 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Thu, Jan 31, 2019 at 12:15:35PM +0900, Masahiro Yamada wrote:
> > Currently, the header search paths -Itools/include and
> > -Itools/include/uapi are not used. Let's drop the unused code.
> >
> > We can remove -I. too by fixing up one C file.
> >
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> > ---
> >
> > Perhaps, are these extra header search paths for
> > more upstreaming in the future?
> >
> > If this patch is rejected, I will send an alternative one.
> >
> > To clean up the Kbuild core,
> > I want to drop as many unused header search paths as possible.
> >
> >
> >  net/bpfilter/Makefile | 1 -
> >  net/bpfilter/main.c   | 2 +-
> >  2 files changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile
> > index 0947ee7..5d6c776 100644
> > --- a/net/bpfilter/Makefile
> > +++ b/net/bpfilter/Makefile
> > @@ -5,7 +5,6 @@
> >
> >  hostprogs-y := bpfilter_umh
> >  bpfilter_umh-objs := main.o
> > -KBUILD_HOSTCFLAGS += -I. -Itools/include/ -Itools/include/uapi
> >  HOSTCC := $(CC)
> >
> >  ifeq ($(CONFIG_BPFILTER_UMH), y)
> > diff --git a/net/bpfilter/main.c b/net/bpfilter/main.c
> > index 1317f10..61ce845 100644
> > --- a/net/bpfilter/main.c
> > +++ b/net/bpfilter/main.c
> > @@ -6,7 +6,7 @@
> >  #include <sys/socket.h>
> >  #include <fcntl.h>
> >  #include <unistd.h>
> > -#include "include/uapi/linux/bpf.h"
> > +#include "../../include/uapi/linux/bpf.h"
>
> argh. that's not pretty.
> I would prefer to keep -I in a makefile


This hunk is not a question.

The code #include "include/uapi/linux/bpf.h" is wrong
if you understand the meaning of #include "..."

https://gcc.gnu.org/onlinedocs/cpp/Search-Path.html


The directive #include "include/uapi/linux/bpf.h"
means the preprocessor should look for this header first
in the path relative to the directory of net/bpfilter/main.c

That is, the preprocessor will look for
net/bpfilter/include/uapi/linux/bpf.h
which obviously does not exist.


I am fixing this because adding -I.
in kernel Makefile is always wrong.
For example, commit 5cd5548ff439b91


-- 
Best Regards
Masahiro Yamada