Re: [PATCH] uapi: fix linux/if_pppol2tp.h userspace compilation errors

From: "Dmitry V. Levin" <redacted>
Date: Tue, 14 Feb 2017 13:33:53 +0300

In file included from /usr/include/linux/l2tp.h:12:0,
                 from /usr/include/linux/if_pppol2tp.h:21,
/usr/include/netinet/in.h:31:8: error: redefinition of 'struct in_addr'

This is protected properly by __UAPI_DEF_IN_ADDR, so whichever gets
included first makes the definition.

This whole thing is designed so that if GLIBC headers are included
first, __UAPI_DEF_IN_ADDR will be defined to zero, therefore
linux/in.h won't try to make the definition.  Otherwise it will.

The facility should not be so fragile that we have to play all
kinds of header ordering games.  We would be imposing the same
strange rules on userspace applications including these headers
which is completely unacceptable.

So if the facility isn't working correctly, let's fix that instead
of fidgeting with include ordering all over the tree.

Thanks.