netdev - [RFC PATCH net-next 11/12] drop_monitor: Allow truncation of dropped packets

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Message-Id: <20190722183134.14516-12-idosch@idosch.org>
Date:   Mon, 22 Jul 2019 21:31:33 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, nhorman@...driver.com, dsahern@...il.com,
        roopa@...ulusnetworks.com, nikolay@...ulusnetworks.com,
        jakub.kicinski@...ronome.com, toke@...hat.com, andy@...yhouse.net,
        f.fainelli@...il.com, andrew@...n.ch, vivien.didelot@...il.com,
        mlxsw@...lanox.com, Ido Schimmel <idosch@...lanox.com>
Subject: [RFC PATCH net-next 11/12] drop_monitor: Allow truncation of dropped packets

From: Ido Schimmel <idosch@...lanox.com>

When sending dropped packets to user space it is not always necessary to
copy the entire packet as usually only the headers are of interest.

Allow user to specify the truncation length and add the original length
of the packet as additional metadata to the netlink message.

By default no truncation is performed.

Signed-off-by: Ido Schimmel <idosch@...lanox.com>
---
 include/uapi/linux/net_dropmon.h |  2 ++
 net/core/drop_monitor.c          | 23 +++++++++++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/include/uapi/linux/net_dropmon.h b/include/uapi/linux/net_dropmon.h
index 7708c8a440a1..eb36b61485ef 100644
--- a/include/uapi/linux/net_dropmon.h
+++ b/include/uapi/linux/net_dropmon.h
@@ -75,6 +75,8 @@ enum net_dm_attr {
 	NET_DM_ATTR_TIMESTAMP,			/* struct timespec */
 	NET_DM_ATTR_PAYLOAD,			/* binary */
 	NET_DM_ATTR_PAD,
+	NET_DM_ATTR_TRUNC_LEN,			/* u32 */
+	NET_DM_ATTR_ORIG_LEN,			/* u32 */
 
 	__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 512935fc235b..5af1e1e8d4d0 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -77,6 +77,7 @@ static unsigned long dm_hw_check_delta = 2*HZ;
 static LIST_HEAD(hw_stats_list);
 
 static enum net_dm_alert_mode net_dm_alert_mode = NET_DM_ALERT_MODE_SUMMARY;
+static u32 net_dm_trunc_len;
 
 struct net_dm_skb_cb {
 	void *pc;
@@ -332,6 +333,8 @@ static size_t net_dm_packet_report_size(size_t payload_len)
 	       nla_total_size(IFNAMSIZ + 1) +
 	       /* NET_DM_ATTR_TIMESTAMP */
 	       nla_total_size(sizeof(struct timespec)) +
+	       /* NET_DM_ATTR_ORIG_LEN */
+	       nla_total_size(sizeof(u32)) +
 	       /* NET_DM_ATTR_PAYLOAD */
 	       nla_total_size(payload_len);
 }
@@ -369,6 +372,9 @@ static int net_dm_packet_report_fill(struct sk_buff *msg, struct sk_buff *skb,
 	    nla_put(msg, NET_DM_ATTR_TIMESTAMP, sizeof(ts), &ts))
 		goto nla_put_failure;
 
+	if (nla_put_u32(msg, NET_DM_ATTR_ORIG_LEN, skb->len))
+		goto nla_put_failure;
+
 	if (!payload_len)
 		goto out;
 
@@ -404,6 +410,8 @@ static void net_dm_packet_report(struct sk_buff *skb)
 
 	/* Ensure packet fits inside a single netlink attribute */
 	payload_len = min_t(size_t, skb->len, NET_DM_MAX_PACKET_SIZE);
+	if (net_dm_trunc_len)
+		payload_len = min_t(size_t, net_dm_trunc_len, payload_len);
 
 	msg = nlmsg_new(net_dm_packet_report_size(payload_len), GFP_KERNEL);
 	if (!msg)
@@ -603,6 +611,16 @@ static int net_dm_alert_mode_set(struct genl_info *info)
 	return 0;
 }
 
+static int net_dm_trunc_len_set(struct genl_info *info)
+{
+	if (!info->attrs[NET_DM_ATTR_TRUNC_LEN])
+		return 0;
+
+	net_dm_trunc_len = nla_get_u32(info->attrs[NET_DM_ATTR_TRUNC_LEN]);
+
+	return 0;
+}
+
 static int net_dm_cmd_config(struct sk_buff *skb,
 			struct genl_info *info)
 {
@@ -618,6 +636,10 @@ static int net_dm_cmd_config(struct sk_buff *skb,
 	if (rc)
 		return rc;
 
+	rc = net_dm_trunc_len_set(info);
+	if (rc)
+		return rc;
+
 	return 0;
 }
 
@@ -676,6 +698,7 @@ static int dropmon_net_event(struct notifier_block *ev_block,
 static const struct nla_policy net_dm_nl_policy[NET_DM_ATTR_MAX + 1] = {
 	[NET_DM_ATTR_UNSPEC] = { .strict_start_type = NET_DM_ATTR_UNSPEC + 1 },
 	[NET_DM_ATTR_ALERT_MODE] = { .type = NLA_U8 },
+	[NET_DM_ATTR_TRUNC_LEN] = { .type = NLA_U32 },
 };
 
 static const struct genl_ops dropmon_ops[] = {
-- 
2.21.0