Re: [PATCH] uapi glibc compat: fix cases where glibc net/if.h is included before linux/if.h

From: Mikko Rapeli <redacted>
Date: Fri, 26 Feb 2016 09:25:13 +0200

(Adding libc-alpha list, review of https://lkml.org/lkml/2016/2/7/89 )

On Wed, Feb 17, 2016 at 10:46:20AM -0500, David Miller wrote:

quoted

From: Mikko Rapeli <redacted>
Date: Sun,  7 Feb 2016 16:03:21 +0200

quoted

@@ -68,6 +72,8 @@
  * @IFF_ECHO: echo sent packets. Volatile.
  */
 enum net_device_flags {
+/* for compatibility with glibc net/if.h */
+#if __UAPI_DEF_IF_NET_DEVICE_FLAGS
 	IFF_UP				= 1<<0,  /* sysfs */
 	IFF_BROADCAST			= 1<<1,  /* volatile */
 	IFF_DEBUG			= 1<<2,  /* sysfs */

@@ -84,11 +90,14 @@ enum net_device_flags {
 	IFF_PORTSEL			= 1<<13, /* sysfs */
 	IFF_AUTOMEDIA			= 1<<14, /* sysfs */
 	IFF_DYNAMIC			= 1<<15, /* sysfs */
+#endif /* __UAPI_DEF_IF_NET_DEVICE_FLAGS */
 	IFF_LOWER_UP			= 1<<16, /* volatile */
 	IFF_DORMANT			= 1<<17, /* volatile */
 	IFF_ECHO			= 1<<18, /* volatile */
 };

This is going to get messy is IFF_LOWER_UP, IFF_DORMANT, and IFF_ECHO
get added the the glibc header.  Why not just handle it now with
another __UAPI_DEF_FOO guard so that the additions to net/if.h can
deal with this case too.

Do you mean that the enum should be protected with a single guard or
should I have one guard for current conflicts and one for the future
if glibc headers include IFF_LOWER_UP and others?

I'm ambivalent about the mechanism, and I'm more concerned about covering
those three values in your change rather than eliding them.