netsniff-ng: Fix tpacketv2-only capturing

We need to set up the RX ring depending on whether tpacket v3 is
available or not. Otherwise end up setting its structure up for tpacket
v3, even though only tpacket v2 is available. This should fix packet
capturing for tpacket v2 (i.e. corrupted frames in pcap).

Reported-by: Mike Reeves <luke@geekempire.com>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

2 files changed, 8 insertions, 1 deletions

diff --git a/built_in.h b/built_in.h
index aab4ef6..92996ce 100644
--- a/built_in.h
+++ b/built_in.h
@@ -96,6 +96,13 @@ typedef uint8_t		u8;
 # define __force		/* unimplemented */
 #endif
 
+/* see config_enabled et al. in linux/kconfig.h for details. */
+#define __ARG_PLACEHOLDER_1 			0,
+#define is_defined(cfg)				_is_defined(cfg)
+#define _is_defined(value)			__is_defined(__ARG_PLACEHOLDER_##value)
+#define __is_defined(arg1_or_junk)		___is_defined(arg1_or_junk 1, 0)
+#define ___is_defined(__ignored, val, ...)	val
+
 #ifndef force_cast
 # define force_cast(type, arg)	((type) (arg))
 #endif
diff --git a/netsniff-ng.c b/netsniff-ng.c
index 78b5666..47edbcd 100644
--- a/netsniff-ng.c
+++ b/netsniff-ng.c
@@ -906,7 +906,7 @@ static void recv_only_or_dump(struct ctx *ctx)
 			printf("HW timestamping enabled\n");
 	}
 
-	ring_rx_setup(&rx_ring, sock, size, ifindex, &rx_poll, true, true, ctx->verbose);
+	ring_rx_setup(&rx_ring, sock, size, ifindex, &rx_poll, is_defined(HAVE_TPACKET3), true, ctx->verbose);
 
 	dissector_init_all(ctx->print_mode);