Subject: Re: [PATCH v2] net, uapi: remove inclusion of arpa/inet.h

From: Jakub Kicinski <[email-masked]>
Date: Tue, 29 Mar 2022 16:01:37 -0700

On Tue, 29 Mar 2022 15:39:56 -0700 Nick Desaulniers 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);
> ^
> 
> 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 not defined in any UAPI header. For now, reuse the
> definitions from include/linux/byteorder/generic.h, since the various
> conversion functions do exist in UAPI headers:
> include/uapi/linux/byteorder/big_endian.h
> include/uapi/linux/byteorder/little_endian.h
> 
> Link: https://android-review.googlesource.com/c/platform/bionic/+/2048127
> Signed-off-by: Nick Desaulniers <[email-masked]>
> ---
>  include/uapi/linux/tipc_config.h | 32 ++++++++++++++++----------------
>  1 file changed, 16 insertions(+), 16 deletions(-)
> 
> diff --git a/include/uapi/linux/tipc_config.h b/include/uapi/linux/tipc_config.h
> index 4dfc05651c98..2c494b7ae008 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

Hm, how do we know no user space depends on this include?

If nobody screams at us we can try, but then it needs to go into -next,
and net-next is closed ATM, you'll need to repost once the merge window
is over.

>  /*
>   * Configuration
>   *
> @@ -257,6 +253,10 @@ struct tlv_desc {
>  #define TLV_SPACE(datalen) (TLV_ALIGN(TLV_LENGTH(datalen)))
>  #define TLV_DATA(tlv) ((void *)((char *)(tlv) + TLV_LENGTH(0)))
>  
> +#define __htonl(x) __cpu_to_be32(x)
> +#define __htons(x) __cpu_to_be16(x)
> +#define __ntohs(x) __be16_to_cpu(x)
> +
>  static inline int TLV_OK(const void *tlv, __u16 space)
>  {
>  	/*
> @@ -269,33 +269,33 @@ static inline int TLV_OK(const void *tlv, __u16 space)
>  	 */
>  
>  	return (space >= TLV_SPACE(0)) &&
> -		(ntohs(((struct tlv_desc *)tlv)->tlv_len) <= space);
> +		(__ntohs(((struct tlv_desc *)tlv)->tlv_len) <= space);

Also why add the defines / macros? 
We could switch to __cpu_to_be16() etc. directly, it seems.