[Linux-kernel-mentees] [PATCH net-next] dropwatch: Support monitoring of dropped frames

[izabela.bakollari at gmail.com]

From: Izabela Bakollari <izabela.bakollari at gmail.com>

Dropwatch is a utility that monitors dropped frames by having userspace
record them over the dropwatch protocol over a file. This augument
allows live monitoring of dropped frames using tools like tcpdump.

With this feature, dropwatch allows two additional commands (start and
stop interface) which allows the assignment of a net_device to the
dropwatch protocol. When assinged, dropwatch will clone dropped frames,
and receive them on the assigned interface, allowing tools like tcpdump
to monitor for them.

With this feature, create a dummy ethernet interface (ip link add dev
dummy0 type dummy), assign it to the dropwatch kernel subsystem, by using
these new commands, and then monitor dropped frames in real time by
running tcpdump -i dummy0.

Signed-off-by: Izabela Bakollari <izabela.bakollari at gmail.com>
---
 include/uapi/linux/net_dropmon.h |  3 ++
 net/core/drop_monitor.c          | 79 +++++++++++++++++++++++++++++++-
 2 files changed, 80 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/net_dropmon.h b/include/uapi/linux/net_dropmon.h
index 67e31f329190..e8e861e03a8a 100644
--- a/include/uapi/linux/net_dropmon.h
+++ b/include/uapi/linux/net_dropmon.h
@@ -58,6 +58,8 @@ enum {
 	NET_DM_CMD_CONFIG_NEW,
 	NET_DM_CMD_STATS_GET,
 	NET_DM_CMD_STATS_NEW,
+	NET_DM_CMD_START_IFC,
+	NET_DM_CMD_STOP_IFC,
 	_NET_DM_CMD_MAX,
 };
 
@@ -93,6 +95,7 @@ enum net_dm_attr {
 	NET_DM_ATTR_SW_DROPS,			/* flag */
 	NET_DM_ATTR_HW_DROPS,			/* flag */
 	NET_DM_ATTR_FLOW_ACTION_COOKIE,		/* binary */
+	NET_DM_ATTR_IFNAME,			/* string */
 
 	__NET_DM_ATTR_MAX,
 	NET_DM_ATTR_MAX = __NET_DM_ATTR_MAX - 1
diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 8e33cec9fc4e..8049bff05abd 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -30,6 +30,7 @@
 #include <net/genetlink.h>
 #include <net/netevent.h>
 #include <net/flow_offload.h>
+#include <net/sock.h>
 
 #include <trace/events/skb.h>
 #include <trace/events/napi.h>
@@ -46,6 +47,7 @@
  */
 static int trace_state = TRACE_OFF;
 static bool monitor_hw;
+struct net_device *interface;
 
 /* net_dm_mutex
  *
@@ -220,9 +222,8 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
 	struct per_cpu_dm_data *data;
 	unsigned long flags;
 
-	local_irq_save(flags);
+	spin_lock_irqsave(&data->lock, flags);
 	data = this_cpu_ptr(&dm_cpu_data);
-	spin_lock(&data->lock);
 	dskb = data->skb;
 
 	if (!dskb)
@@ -255,6 +256,12 @@ static void trace_drop_common(struct sk_buff *skb, void *location)
 
 out:
 	spin_unlock_irqrestore(&data->lock, flags);
+
+	if (interface && interface != skb->dev) {
+		skb = skb_clone(skb, GFP_ATOMIC);
+		skb->dev = interface;
+		netif_receive_skb(skb);
+	}
 }
 
 static void trace_kfree_skb_hit(void *ignore, struct sk_buff *skb, void *location)
@@ -1315,6 +1322,63 @@ static int net_dm_cmd_trace(struct sk_buff *skb,
 	return -EOPNOTSUPP;
 }
 
+static int net_dm_interface_start(struct net *net, const char *ifname)
+{
+	struct net_device *nd;
+
+	nd = dev_get_by_name(net, ifname);
+
+	if (nd) {
+		interface = nd;
+		dev_hold(interface);
+	} else {
+		return -ENODEV;
+	}
+	return 0;
+}
+
+static int net_dm_interface_stop(struct net *net, const char *ifname)
+{
+	struct net_device *nd;
+
+	nd = dev_get_by_name(net, ifname);
+
+	if (nd) {
+		interface = nd;
+		dev_put(interface);
+	} else {
+		return -ENODEV;
+	}
+	return 0;
+}
+
+static int net_dm_cmd_ifc_trace(struct sk_buff *skb, struct genl_info *info)
+{
+	struct net *net = sock_net(skb->sk);
+	char ifname[IFNAMSIZ];
+	int rc;
+
+	memset(ifname, 0, IFNAMSIZ);
+	nla_strlcpy(ifname, info->attrs[NET_DM_ATTR_IFNAME], IFNAMSIZ - 1);
+
+	switch (info->genlhdr->cmd) {
+	case NET_DM_CMD_START_IFC:
+		rc = net_dm_interface_start(net, ifname);
+		if (rc)
+			return rc;
+		break;
+	case NET_DM_CMD_STOP_IFC:
+		if (interface) {
+			rc = net_dm_interface_stop(net, interface->ifname);
+			return rc;
+		} else {
+			return -ENODEV;
+		}
+	}
+
+	return 0;
+}
+
 static int net_dm_config_fill(struct sk_buff *msg, struct genl_info *info)
 {
 	void *hdr;
@@ -1543,6 +1607,7 @@ static const struct nla_policy net_dm_nl_policy[NET_DM_ATTR_MAX + 1] = {
 	[NET_DM_ATTR_QUEUE_LEN] = { .type = NLA_U32 },
 	[NET_DM_ATTR_SW_DROPS]	= {. type = NLA_FLAG },
 	[NET_DM_ATTR_HW_DROPS]	= {. type = NLA_FLAG },
+	[NET_DM_ATTR_IFNAME] = {. type = NLA_STRING, .len = IFNAMSIZ },
 };
 
 static const struct genl_ops dropmon_ops[] = {
@@ -1570,6 +1635,16 @@ static const struct genl_ops dropmon_ops[] = {
 		.cmd = NET_DM_CMD_STATS_GET,
 		.doit = net_dm_cmd_stats_get,
 	},
+	{
+		.cmd = NET_DM_CMD_START_IFC,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit = net_dm_cmd_ifc_trace,
+	},
+	{
+		.cmd = NET_DM_CMD_STOP_IFC,
+		.validate = GENL_DONT_VALIDATE_STRICT | GENL_DONT_VALIDATE_DUMP,
+		.doit = net_dm_cmd_ifc_trace,
+	},
 };
 
 static int net_dm_nl_pre_doit(const struct genl_ops *ops,
-- 
2.18.4