linux-kernel - Re: [PATCH] net, uapi: remove inclusion of arpa/inet.h

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Date:   Tue, 29 Mar 2022 16:03:57 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Masahiro Yamada <masahiroy@...nel.org>,
        Arnd Bergmann <arnd@...db.de>
Cc:     Nathan Chancellor <nathan@...nel.org>, netdev@...r.kernel.org,
        tipc-discussion@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        David Howells <dhowells@...hat.com>,
        Ying Xue <ying.xue@...driver.com>,
        Jon Maloy <jmaloy@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] net, uapi: remove inclusion of arpa/inet.h

On Tue, Mar 29, 2022 at 3:09 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> On Tue, Mar 29, 2022 at 2:50 PM Nick Desaulniers
> <ndesaulniers@...gle.com> wrote:
> >
> > On Tue, Mar 29, 2022 at 2:29 PM Nick Desaulniers
> > <ndesaulniers@...gle.com> wrote:
> > >
> > > Testing out CONFIG_UAPI_HEADER_TEST=y with a prebuilt Bionic sysroot
> > > from Android's SDK, I encountered an error:
> > >
> > >   HDRTEST usr/include/linux/fsi.h
> > > In file included from <built-in>:1:
> > > In file included from ./usr/include/linux/tipc_config.h:46:
> > > prebuilts/ndk/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/include/arpa/inet.h:39:1:
> > > error: unknown type name 'in_addr_t'
> > > in_addr_t inet_addr(const char* __s);
> > > ^
> >
> > Oh, this might not quite be the correct fix for this particular issue.
> >
> > Cherry picking this diff back into my Android kernel tree, I now observe:
> >   HDRTEST usr/include/linux/tipc_config.h
> > In file included from <built-in>:1:
> > ./usr/include/linux/tipc_config.h:268:4: error: implicit declaration
> > of function 'ntohs' [-Werror,-Wimplicit-function-declaration]
> >                 (ntohs(((struct tlv_desc *)tlv)->tlv_len) <= space);
> >                  ^
> >
> > Is there more than one byteorder.h? Oh, I see what I did; ntohs is defined in
> > linux/byteorder/generic.h
> > not
> > usr/include/asm/byteorder.h
> > Sorry, I saw `byteorder` and mixed up the path with the filename.
> >
> > So rather than just remove the latter, I should additionally be adding
> > the former. Though that then produces
> >
> > common/include/linux/byteorder/generic.h:146:9: error: implicit
> > declaration of function '__cpu_to_le16'
> > [-Werror,-Wimplicit-function-declaration]
> >         *var = cpu_to_le16(le16_to_cpu(*var) + val);
> >                ^
> >
> > Oh?
>
> Should there be a definition of ntohs (and friends) under
> include/uapi/linux/ somewhere, rather than have the kernel header
> include/uapi/linux/tipc_config.h depend on the libc header
> arpa/inet.h?
>
> It looks like we already have
> include/uapi/linux/byteorder/{big|little}_endian.h to define
> __be16_to_cpu and friends, just no definition of ntohs under
> include/uapi/linux/.
>
> Also, it looks like include/uapi/linux/ has definitions for
> __constant_ntohs in
> include/uapi/linux/byteorder/{big|little}_endian.h.  Should those 2
> headers also define ntohs (and friends) unprefixed, i.e. the versions
> that don't depend on constant expressions?
>
> (I wish there was an entry in MAINTAINERS for UAPI questions like this...)

I also think that Documentation/kbuild/headers_install.rst should
probably include text from
https://lore.kernel.org/all/Pine.LNX.4.58.0411281710490.22796@ppc970.osdl.org/
or something along the lines of "kernel headers MUST NOT depend on
userspace headers; any instance of that in tree is a bug that should
be fixed."

For people I just cc'ed, here's the lore link to this thread:
https://lore.kernel.org/lkml/20220329212946.2861648-1-ndesaulniers@google.com/

>
> >
> > >
> > > This is because Bionic has a bug in its inclusion chain. I sent a patch
> > > to fix that, but looking closer at include/uapi/linux/tipc_config.h,
> > > there's a comment that it includes arpa/inet.h for ntohs; but ntohs is
> > > already defined in include/linux/byteorder/generic.h which is already
> > > included in include/uapi/linux/tipc_config.h. There are no __KERNEL__
> > > guards on include/linux/byteorder/generic.h's definition of ntohs. So
> > > besides fixing Bionic, it looks like we can additionally remove this
> > > unnecessary header inclusion.
> > >
> > > Link: https://android-review.googlesource.com/c/platform/bionic/+/2048127
> > > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > > ---
> > >  include/uapi/linux/tipc_config.h | 4 ----
> > >  1 file changed, 4 deletions(-)
> > >
> > > diff --git a/include/uapi/linux/tipc_config.h b/include/uapi/linux/tipc_config.h
> > > index 4dfc05651c98..b38374d5f192 100644
> > > --- a/include/uapi/linux/tipc_config.h
> > > +++ b/include/uapi/linux/tipc_config.h
> > > @@ -43,10 +43,6 @@
> > >  #include <linux/tipc.h>
> > >  #include <asm/byteorder.h>
> > >
> > > -#ifndef __KERNEL__
> > > -#include <arpa/inet.h> /* for ntohs etc. */
> > > -#endif
> > > -
> > >  /*
> > >   * Configuration
> > >   *
> > >
> > > base-commit: 5efabdadcf4a5b9a37847ecc85ba71cf2eff0fcf
> > > prerequisite-patch-id: 0c2abf2af8051f4b37a70ef11b7d2fc2a3ec7181
> > > --
> > > 2.35.1.1021.g381101b075-goog
> > >
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
>
>
>
> --
> Thanks,
> ~Nick Desaulniers



-- 
Thanks,
~Nick Desaulniers