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

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Date:   Tue, 29 Mar 2022 15:09:59 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Jon Maloy <jmaloy@...hat.com>, Ying Xue <ying.xue@...driver.com>,
        Arnd Bergmann <arnd@...db.de>,
        Masahiro Yamada <masahiroy@...nel.org>
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>
Subject: Re: [PATCH] net, uapi: remove inclusion of arpa/inet.h

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...)

>
> >
> > 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