[PATCH bpf] bpftool: fix compilation failure for net.o with older glibc

For older glibc ~2.17, #include'ing both linux/if.h and net/if.h
fails due to complaints about redefinition of interface flags:

  CC       net.o
In file included from net.c:13:0:
/usr/include/linux/if.h:71:2: error: redeclaration of enumerator ‘IFF_UP’
  IFF_UP    = 1<<0,  /* sysfs */
  ^
/usr/include/net/if.h:44:5: note: previous definition of ‘IFF_UP’ was here
     IFF_UP = 0x1,  /* Interface is up.  */

The issue was fixed in kernel headers in [1], but since compilation
of net.c picks up system headers the problem can recur.

Dropping #include <linux/if.h> resolves the issue and it is
not needed for compilation anyhow.

[1] https://lore.kernel.org/netdev/1461512707-23058-1-git-send-email-mikko.rapeli__34748.27880641$1462831734$gmane$org@iki.fi/

Fixes: f6f3bac08ff9 ("tools/bpf: bpftool: add net support")
Signed-off-by: Alan Maguire <redacted>
---
 tools/bpf/bpftool/net.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tools/bpf/bpftool/net.c b/tools/bpf/bpftool/net.c
index 3fae61e..ff3aa0c 100644
--- a/tools/bpf/bpftool/net.c
+++ b/tools/bpf/bpftool/net.c

@@ -11,7 +11,6 @@
 #include <bpf/bpf.h>
 #include <bpf/libbpf.h>
 #include <net/if.h>
-#include <linux/if.h>
 #include <linux/rtnetlink.h>
 #include <linux/socket.h>
 #include <linux/tc_act/tc_bpf.h>

-- 
1.8.3.1

On Wed, Jan 06, 2021 at 03:59:06PM +0000, Alan Maguire wrote:

For older glibc ~2.17, #include'ing both linux/if.h and net/if.h
fails due to complaints about redefinition of interface flags:

  CC       net.o
In file included from net.c:13:0:
/usr/include/linux/if.h:71:2: error: redeclaration of enumerator ‘IFF_UP’
  IFF_UP    = 1<<0,  /* sysfs */
  ^
/usr/include/net/if.h:44:5: note: previous definition of ‘IFF_UP’ was here
     IFF_UP = 0x1,  /* Interface is up.  */

The issue was fixed in kernel headers in [1], but since compilation
of net.c picks up system headers the problem can recur.

Dropping #include <linux/if.h> resolves the issue and it is
not needed for compilation anyhow.

Acked-by: Martin KaFai Lau <redacted>

Hello:

This patch was applied to bpf/bpf.git (refs/heads/master):

On Wed,  6 Jan 2021 15:59:06 +0000 you wrote:

For older glibc ~2.17, #include'ing both linux/if.h and net/if.h
fails due to complaints about redefinition of interface flags:

  CC       net.o
In file included from net.c:13:0:
/usr/include/linux/if.h:71:2: error: redeclaration of enumerator ‘IFF_UP’
  IFF_UP    = 1<<0,  /* sysfs */
  ^
/usr/include/net/if.h:44:5: note: previous definition of ‘IFF_UP’ was here
     IFF_UP = 0x1,  /* Interface is up.  */

[...]

Here is the summary with links:
  - [bpf] bpftool: fix compilation failure for net.o with older glibc
    https://git.kernel.org/bpf/bpf/c/6f02b540d759

You are awesome, thank you!
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