On 04/07/2015 04:20 PM, Laine Stump wrote:
When netcf first include support for libnl3, the author of that
patch
(Serge Hallyn, commit 0310cd505) found that
/usr/include/libnl3/netlink/route/link.h #included <linux/if.h>, which
conflicts with <net/if.h> (but for our purposes at least defines all the
same things). So he put the #include <net/if.h> in dutil_linux.c inside
an #ifndef HAVE_LIBNL3.
That worked fine until libnl3 finally removed the offending (and
unnecessary) #include <linux/if.h> from its link.h. That fix to libnl3
broke the netcf build.
This patch fixes the build by using autotools magic to attempt
compiling essentially this short program:
#include <netlink/route/link.h>
int main()
{
int try = IFF_UP;
struct ifreq ifr;
return 0;
If someone configures with high levels of warnings enabled, this might
spuriously fail due to unused variables. Something like:
struct ifreq ifr;
return ifr.ifr_ivalue = IFF_UP;
is slightly stronger (nothing goes unused), even if weird (no one would
actually write this anywhere besides configure.ac). Then again, the
autoconf list frequently tells people that run './configure
CFLAGS=-Werror' to not do it - there is NO way to write warning-free
code for every possible compiler version, especially when probing for
features; and therefore worrying about compiler warnings in configure
snippets is not worth the effort. So I would not bother rewriting the
code _unless_ someone complains that it has a false failure during
configure, which I doubt will happen.
}
If this can compile successfully without any other includes, then
link.h is already including linux/if.h and we should avoid including
net/if.h, so we #define AVOID_NET_IF_H. If the compile fails, then we
do need to include net/if.h, so we *don't* #define
AVOID_NET_IF_H. Then we enclose dutil_linux.c's #include <net/if.h>
within #ifndef AVOID_NET_IF_H and we're done.
Although this check would probably be safe on a libnl1 system, we know
from past experience that we should always include net/if.h in those
cases anyway, so we don't even try - we only do the configure-time
check if we're using libnl3.
---
configure.ac | 19 ++++++++++++++++++-
src/dutil_linux.c | 4 ++--
2 files changed, 20 insertions(+), 3 deletions(-)
diff --git a/configure.ac b/configure.ac
index a914b0f..6edbb5e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -164,7 +164,24 @@ then
if (test "${have_libnl3}" = "yes" -a
"${have_libnl_route3}" = "yes"); then
AC_DEFINE([HAVE_LIBNL3], [1], [Use libnl-3.0])
have_libnl="yes"
- else
+ SAVE_CFLAGS="${CFLAGS}"
Difference in TAB vs. space (not fatal, but you may want to be consistent)
+ CFLAGS="${LIBNL_CFLAGS} ${CFLAGS}"
+ dnl Avoid #including net/if.h when using earlier versions
+ dnl of libnl3 that include linux/if.h from netlink/route/link.h,
+ dnl since the two if.h files conflict with each other.
+ AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+ [[
+ #include <netlink/route/link.h>
+ ]],
+ [[struct ifreq ifr; int try = IFF_UP;]])],
+ [avoid_net_if_h=yes], [avoid_net_if_h=no])
Looks correct. The only improvement might be to wrap it all in
AC_CACHE_CHECK and rename the witness variable to something like
netcf_cv_avoid_net_if_h, so that it can be primed through a configure
cache rather than probed every time. Again, not sure it would matter
until someone actually complains that it guessed wrong and they wished
for a way to prime the cache to avoid the wrong guess.
+ CFLAGS="${SAVE_CFLAGS}"
+ if test "x$avoid_net_if_h" = "xyes"; then
+ AC_DEFINE([AVOID_NET_IF_H], [1],
+ [define to 1 if the libnl3 header netlink/route/link.h
already
+ includes linux/if.h (which will conflict with net/if.h)])
technically, it conflicts with net/if.h only in some versions of the
kernel headers, but I can't think of any concise wording for that.
+ fi
+ else
PKG_CHECK_MODULES([LIBNL], [libnl-1],
[have_libnl1=yes],
[have_libnl1=no])
diff --git a/src/dutil_linux.c b/src/dutil_linux.c
index 299b36e..0850593 100644
--- a/src/dutil_linux.c
+++ b/src/dutil_linux.c
@@ -54,8 +54,8 @@
#include "dutil.h"
#include "dutil_linux.h"
-#ifndef HAVE_LIBNL3
-#include <net/if.h>
+#ifndef AVOID_NET_IF_H
+# include <net/if.h>
#endif
#include <netlink/socket.h>
#include <netlink/cache.h>
ACK.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library
http://libvirt.org