3 files changed, 44 insertions, 22 deletions

diff --git a/pcap.c b/pcap.c
index 3d623cf..e95aa6f 100644
--- a/pcap.c
+++ b/pcap.c
@@ -33,33 +33,12 @@
 #include "log.h"
 #include "pcap.h"
 #include "iov.h"
+#include "tap.h"
 
 #define PCAP_VERSION_MINOR 4
 
 static int pcap_fd = -1;
 
-/* See pcap.h from libpcap, or pcap-savefile(5) */
-static const struct {
-	uint32_t magic;
-#define PCAP_MAGIC		0xa1b2c3d4
-
-	uint16_t major;
-#define PCAP_VERSION_MAJOR	2
-
-	uint16_t minor;
-#define PCAP_VERSION_MINOR	4
-
-	int32_t thiszone;
-	uint32_t sigfigs;
-	uint32_t snaplen;
-
-	uint32_t linktype;
-#define PCAP_LINKTYPE_ETHERNET	1
-} pcap_hdr = {
-	PCAP_MAGIC, PCAP_VERSION_MAJOR, PCAP_VERSION_MINOR, 0, 0, ETH_MAX_MTU,
-	PCAP_LINKTYPE_ETHERNET
-};
-
 struct pcap_pkthdr {
 	uint32_t tv_sec;
 	uint32_t tv_usec;
@@ -162,6 +141,29 @@ void pcap_iov(const struct iovec *iov, size_t iovcnt, size_t offset)
  */
 void pcap_init(struct ctx *c)
 {
+	/* See pcap.h from libpcap, or pcap-savefile(5) */
+#define PCAP_MAGIC		0xa1b2c3d4
+#define PCAP_VERSION_MAJOR	2
+#define PCAP_VERSION_MINOR	4
+#define PCAP_LINKTYPE_ETHERNET	1
+	const struct {
+		uint32_t magic;
+		uint16_t major;
+		uint16_t minor;
+
+		int32_t thiszone;
+		uint32_t sigfigs;
+		uint32_t snaplen;
+
+		uint32_t linktype;
+	} pcap_hdr = {
+		.magic = PCAP_MAGIC,
+		.major = PCAP_VERSION_MAJOR,
+		.minor = PCAP_VERSION_MINOR,
+		.snaplen = tap_l2_max_len(c),
+		.linktype = PCAP_LINKTYPE_ETHERNET
+	};
+
 	if (pcap_fd != -1)
 		return;
 
diff --git a/tap.c b/tap.c
index ede547c..182a115 100644
--- a/tap.c
+++ b/tap.c
@@ -83,6 +83,25 @@ static PACKET_POOL_NOINIT(pool_tap6, TAP_MSGS, pkt_buf);
 #define FRAGMENT_MSG_RATE	10  /* # seconds between fragment warnings */
 
 /**
+ * tap_l2_max_len() - Maximum frame size (including L2 header) for current mode
+ * @c:		Execution context
+ */
+unsigned long tap_l2_max_len(const struct ctx *c)
+{
+	/* NOLINTBEGIN(bugprone-branch-clone): values can be the same */
+	switch (c->mode) {
+	case MODE_PASST:
+		return L2_MAX_LEN_PASST;
+	case MODE_PASTA:
+		return L2_MAX_LEN_PASTA;
+	case MODE_VU:
+		return L2_MAX_LEN_VU;
+	}
+	/* NOLINTEND(bugprone-branch-clone) */
+	ASSERT(0);
+}
+
+/**
  * tap_send_single() - Send a single frame
  * @c:		Execution context
  * @data:	Packet buffer
diff --git a/tap.h b/tap.h
index 84e9fdb..dd39fd8 100644
--- a/tap.h
+++ b/tap.h
@@ -69,6 +69,7 @@ static inline void tap_hdr_update(struct tap_hdr *thdr, size_t l2len)
 		thdr->vnet_len = htonl(l2len);
 }
 
+unsigned long tap_l2_max_len(const struct ctx *c);
 void *tap_push_l2h(const struct ctx *c, void *buf, uint16_t proto);
 void *tap_push_ip4h(struct iphdr *ip4h, struct in_addr src,
 		     struct in_addr dst, size_t l4len, uint8_t proto);