netsniff-ng: Add command line option to disable hardware time stamping

Allow to disable hardware time stamping using the command line switch
(-N/--no-hwtimestamp). This might be useful in situations where hardware
time stamps are skewed somehow.

Reference: #129
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

3 files changed, 21 insertions, 5 deletions

diff --git a/netsniff-ng.8 b/netsniff-ng.8
index c6356bf..b6f129a 100644
--- a/netsniff-ng.8
+++ b/netsniff-ng.8
@@ -153,6 +153,13 @@ randomize packet order in the output ring buffer.
 The networking interface will not be put into promiscuous mode. By default,
 promiscuous mode is turned on.
 .PP
+.SS -N, --no-hwtimestamp
+Disable taking hardware time stamps for RX packets. By default, if the network
+device supports hardware time stamping, the hardware time stamps will be used
+when writing packets to pcap files. This option disables this behavior and
+forces (kernel based) software time stamps to be used, even if hardware time
+stamps are available.
+.PP
 .SS -A, --no-sock-mem
 On startup and shutdown, netsniff-ng tries to increase socket read and
 write buffers if appropriate. This option will prevent netsniff-ng from doing
diff --git a/netsniff-ng.c b/netsniff-ng.c
index 397f50d..af36d5c 100644
--- a/netsniff-ng.c
+++ b/netsniff-ng.c
@@ -57,7 +57,7 @@ struct ctx {
 	int cpu, rfraw, dump, print_mode, dump_dir, packet_type;
 	unsigned long kpull, dump_interval, tx_bytes, tx_packets;
 	size_t reserve_size;
-	bool randomize, promiscuous, enforce, jumbo, dump_bpf, verbose;
+	bool randomize, promiscuous, enforce, jumbo, dump_bpf, hwtimestamp, verbose;
 	enum pcap_ops_groups pcap; enum dump_mode dump_mode;
 	uid_t uid; gid_t gid; uint32_t link_type, magic;
 };
@@ -65,7 +65,7 @@ struct ctx {
 static volatile sig_atomic_t sigint = 0;
 static volatile bool next_dump = false;
 
-static const char *short_options = "d:i:o:rf:MJt:S:k:n:b:HQmcsqXlvhF:RGAP:Vu:g:T:DBU";
+static const char *short_options = "d:i:o:rf:MNJt:S:k:n:b:HQmcsqXlvhF:RGAP:Vu:g:T:DBU";
 static const struct option long_options[] = {
 	{"dev",			required_argument,	NULL, 'd'},
 	{"in",			required_argument,	NULL, 'i'},
@@ -88,6 +88,7 @@ static const struct option long_options[] = {
 	{"clrw",		no_argument,		NULL, 'c'},
 	{"jumbo-support",	no_argument,		NULL, 'J'},
 	{"no-promisc",		no_argument,		NULL, 'M'},
+	{"no-hwtimestamp",	no_argument,		NULL, 'N'},
 	{"prio-high",		no_argument,		NULL, 'H'},
 	{"notouch-irq",		no_argument,		NULL, 'Q'},
 	{"dump-pcap-types",	no_argument,		NULL, 'D'},
@@ -890,9 +891,11 @@ static void recv_only_or_dump(struct ctx *ctx)
 		bpf_dump_all(&bpf_ops);
 	bpf_attach_to_sock(sock, &bpf_ops);
 
-	ret = set_sockopt_hwtimestamp(sock, ctx->device_in);
-	if (ret == 0 && ctx->verbose)
-		printf("HW timestamping enabled\n");
+	if (ctx->hwtimestamp) {
+		ret = set_sockopt_hwtimestamp(sock, ctx->device_in);
+		if (ret == 0 && ctx->verbose)
+			printf("HW timestamping enabled\n");
+	}
 
 	ring_rx_setup(&rx_ring, sock, size, ifindex, &rx_poll, true, true, ctx->verbose);
 
@@ -1005,6 +1008,7 @@ static void init_ctx(struct ctx *ctx)
 
 	ctx->promiscuous = true;
 	ctx->randomize = false;
+	ctx->hwtimestamp = true;
 }
 
 static void destroy_ctx(struct ctx *ctx)
@@ -1036,6 +1040,7 @@ static void __noreturn help(void)
 	     "  -r|--rand                      Randomize packet forwarding order (dev->dev)\n"
 	     "  -M|--no-promisc                No promiscuous mode for netdev\n"
 	     "  -A|--no-sock-mem               Don't tune core socket memory\n"
+	     "  -N|--no-hwtimestamp            Disable hardware time stamping\n"
 	     "  -m|--mmap                      Mmap(2) pcap file I/O, e.g. for replaying pcaps\n"
 	     "  -G|--sg                        Scatter/gather pcap file I/O\n"
 	     "  -c|--clrw                      Use slower read(2)/write(2) I/O\n"
@@ -1138,6 +1143,9 @@ int main(int argc, char **argv)
 		case 'M':
 			ctx.promiscuous = false;
 			break;
+		case 'N':
+			ctx.hwtimestamp = false;
+			break;
 		case 'A':
 			setsockmem = false;
 			break;
diff --git a/netsniff-ng.zsh b/netsniff-ng.zsh
index 682d66d..f60f867 100644
--- a/netsniff-ng.zsh
+++ b/netsniff-ng.zsh
@@ -47,6 +47,7 @@ _arguments -s -S \
     "(-B --dump-bpf)"{-B,--dump-bpf}"[Dump generated BPF assembly]" \
     "(-r --rand)"{-r,--rand}"[Randomize packet forwarding order (dev->dev)]" \
     "(-M --no-promisc)"{-M,--no-promisc}"[No promiscuous mode for netdev]" \
+    "(-N --no-hwtimestamp)"{-N,--no-hwtimestamp}"[Disable hardware timestamping]" \
     "(-A --no-sock-mem)"{-A,--no-sock-mem}"[Don\'t tune core socket memory]" \
     "(-m --mmap)"{-m,--mmap}"[Mmap(2) pcap file i.e., for replaying pcaps]" \
     "(-G --sg)"{-G,--sg}"[Scatter/gather pcap file I/O]" \