Makefile, tcp: Don't try to use tcpi_snd_wnd from tcp_info on pre-5.3 kernels

Detect missing tcpi_snd_wnd in struct tcp_info at build time,
otherwise build fails with a pre-5.3 linux/tcp.h header.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 85d7400..83140ad 100644
--- a/Makefile
+++ b/Makefile
@@ -29,6 +29,11 @@ endif
 endif
 endif
 
+C := \#include <linux/tcp.h>\nstruct tcp_info x = { .tcpi_snd_wnd = 0 };
+ifeq ($(shell printf "$(C)" | $(CC) -S -xc - -o - >/dev/null 2>&1; echo $$?),0)
+	CFLAGS += -DHAS_SND_WND
+endif
+
 prefix ?= /usr/local
 
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