Subject: Re: include/linux/netlink.h: problem when included by an application

From: Ben Hutchings <[email-masked]>
Date: Sun, 07 Aug 2011 02:15:07 +0100

On Fri, 2011-08-05 at 17:45 -0400, Michel Machado wrote:
> Hi there,
> 
>    When an application includes header <linux/netlink.h> obtained with
> 'make headers_install' or from /usr/include/, it produces the following
> error:
> 
> /usr/include/linux/netlink.h:31:2: error: expected
> specifier-qualifier-list before ‘sa_family_t’

Yeah, I know.

>    The error doesn't come up in the kernel because
> include/linux/netlink.h has the following line:
> 
> #include <linux/socket.h> /* for sa_family_t */
> 
>    However, <linux/socket.h> from /usr/include/ doesn't have sa_family_t
> because it's protected by an $ifdef __KERNEL__ in
> include/linux/socket.h.

Which is correct, as it would otherwise conflict with <sys/socket.h>.

Previous history:
http://thread.gmane.org/gmane.linux.debian.devel.bugs.general/622621
http://thread.gmane.org/gmane.linux.network/143380

>    A workaround for an application is to include <sys/socket.h> before
> <linux/netlink.h>. However, shouldn't include/linux/netlink.h be fixed?
> 
>    The simplest solution that I came up was replacing sa_family_t in
> include/linux/netlink.h to 'unsigned short' as header
> include/linux/socket.h does for struct __kernel_sockaddr_storage
> available to applications.

Maybe we should do something like this in <linux/socket.h>:

typedef unsigned short __kernel_sa_family_t;
#ifdef __KERNEL__
typedef __kernel_sa_family_t sa_family_t;
#endif

and then use __kernel_sa_family_t in <linux/netlink.h>.

Ben.