Subject: Re: [net-next v4 1/7] net: openvswitch: add last-action drop reason

From: Aaron Conole <[email-masked]>
Date: Thu, 10 Aug 2023 14:13:29 -0400

Adrian Moreno <[email-masked]> writes:

> Create a new drop reason subsystem for openvswitch and add the first
> drop reason to represent last-action drops.
>
> Last-action drops happen when a flow has an empty action list or there
> is no action that consumes the packet (output, userspace, recirc, etc).
> It is the most common way in which OVS drops packets.
>
> Implementation-wise, most of these skb-consuming actions already call
> "consume_skb" internally and return directly from within the
> do_execute_actions() loop so with minimal changes we can assume that
> any skb that exits the loop normally is a packet drop.
>
> Signed-off-by: Adrian Moreno <[email-masked]>
> ---

Overall, looks good.  I did a build with this and got some warnings.  I
think they can be resolved in the same way the mac80211 drops are
resolved by using (__force u32) to pass the reason argument.

>  include/net/dropreason.h   |  6 ++++++
>  net/openvswitch/actions.c  | 12 ++++++++++--
>  net/openvswitch/datapath.c | 16 ++++++++++++++++
>  net/openvswitch/drop.h     | 24 ++++++++++++++++++++++++
>  4 files changed, 56 insertions(+), 2 deletions(-)
>  create mode 100644 net/openvswitch/drop.h
>
> diff --git a/include/net/dropreason.h b/include/net/dropreason.h
> index 685fb37df8e8..56cb7be92244 100644
> --- a/include/net/dropreason.h
> +++ b/include/net/dropreason.h
> @@ -23,6 +23,12 @@ enum skb_drop_reason_subsys {
>  	 */
>  	SKB_DROP_REASON_SUBSYS_MAC80211_MONITOR,
>  
> +	/**
> +	 * @SKB_DROP_REASON_SUBSYS_OPENVSWITCH: openvswitch drop reasons,
> +	 * see net/openvswitch/drop.h
> +	 */
> +	SKB_DROP_REASON_SUBSYS_OPENVSWITCH,
> +
>  	/** @SKB_DROP_REASON_SUBSYS_NUM: number of subsystems defined */
>  	SKB_DROP_REASON_SUBSYS_NUM
>  };
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index cab1e02b63e0..1234e95a9ce8 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -27,6 +27,7 @@
>  #include <net/sctp/checksum.h>
>  
>  #include "datapath.h"
> +#include "drop.h"
>  #include "flow.h"
>  #include "conntrack.h"
>  #include "vport.h"
> @@ -1036,7 +1037,7 @@ static int sample(struct datapath *dp, struct sk_buff *skb,
>  	if ((arg->probability != U32_MAX) &&
>  	    (!arg->probability || get_random_u32() > arg->probability)) {
>  		if (last)
> -			consume_skb(skb);
> +			kfree_skb_reason(skb, OVS_DROP_LAST_ACTION);
>  		return 0;
>  	}
>  
> @@ -1297,6 +1298,9 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
>  		if (trace_ovs_do_execute_action_enabled())
>  			trace_ovs_do_execute_action(dp, skb, key, a, rem);
>  
> +		/* Actions that rightfully have to consume the skb should do it
> +		 * and return directly.
> +		 */
>  		switch (nla_type(a)) {
>  		case OVS_ACTION_ATTR_OUTPUT: {
>  			int port = nla_get_u32(a);
> @@ -1332,6 +1336,10 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
>  			output_userspace(dp, skb, key, a, attr,
>  						     len, OVS_CB(skb)->cutlen);
>  			OVS_CB(skb)->cutlen = 0;
> +			if (nla_is_last(a, rem)) {
> +				consume_skb(skb);
> +				return 0;
> +			}
>  			break;
>  
>  		case OVS_ACTION_ATTR_HASH:
> @@ -1485,7 +1493,7 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
>  		}
>  	}
>  
> -	consume_skb(skb);
> +	kfree_skb_reason(skb, OVS_DROP_LAST_ACTION);
>  	return 0;
>  }
>  
> diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c
> index a6d2a0b1aa21..d33cb739883f 100644
> --- a/net/openvswitch/datapath.c
> +++ b/net/openvswitch/datapath.c
> @@ -41,6 +41,7 @@
>  #include <net/pkt_cls.h>
>  
>  #include "datapath.h"
> +#include "drop.h"
>  #include "flow.h"
>  #include "flow_table.h"
>  #include "flow_netlink.h"
> @@ -2702,6 +2703,17 @@ static struct pernet_operations ovs_net_ops = {
>  	.size = sizeof(struct ovs_net),
>  };
>  
> +static const char * const ovs_drop_reasons[] = {
> +#define S(x)	(#x),
> +	OVS_DROP_REASONS(S)
> +#undef S
> +};
> +
> +static struct drop_reason_list drop_reason_list_ovs = {
> +	.reasons = ovs_drop_reasons,
> +	.n_reasons = ARRAY_SIZE(ovs_drop_reasons),
> +};
> +
>  static int __init dp_init(void)
>  {
>  	int err;
> @@ -2743,6 +2755,9 @@ static int __init dp_init(void)
>  	if (err < 0)
>  		goto error_unreg_netdev;
>  
> +	drop_reasons_register_subsys(SKB_DROP_REASON_SUBSYS_OPENVSWITCH,
> +				     &drop_reason_list_ovs);
> +
>  	return 0;
>  
>  error_unreg_netdev:
> @@ -2769,6 +2784,7 @@ static void dp_cleanup(void)
>  	ovs_netdev_exit();
>  	unregister_netdevice_notifier(&ovs_dp_device_notifier);
>  	unregister_pernet_device(&ovs_net_ops);
> +	drop_reasons_unregister_subsys(SKB_DROP_REASON_SUBSYS_OPENVSWITCH);
>  	rcu_barrier();
>  	ovs_vport_exit();
>  	ovs_flow_exit();
> diff --git a/net/openvswitch/drop.h b/net/openvswitch/drop.h
> new file mode 100644
> index 000000000000..ffdb8ab045bd
> --- /dev/null
> +++ b/net/openvswitch/drop.h
> @@ -0,0 +1,24 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * OpenvSwitch drop reason list.
> + */
> +
> +#ifndef OPENVSWITCH_DROP_H
> +#define OPENVSWITCH_DROP_H
> +#include <net/dropreason.h>
> +
> +#define OVS_DROP_REASONS(R)			\
> +	R(OVS_DROP_LAST_ACTION)		        \
> +	/* deliberate comment for trailing \ */
> +
> +enum ovs_drop_reason {
> +	__OVS_DROP_REASON = SKB_DROP_REASON_SUBSYS_OPENVSWITCH <<
> +				SKB_DROP_REASON_SUBSYS_SHIFT,
> +#define ENUM(x) x,
> +	OVS_DROP_REASONS(ENUM)
> +#undef ENUM
> +
> +	OVS_DROP_MAX,
> +};
> +
> +#endif /* OPENVSWITCH_DROP_H */