af_packet: Add Queue mapping mode to af_packet fanout operation

This patch adds a queue mapping mode to the fanout operation of af_packet
sockets. This allows user space af_packet users to better filter on flows
ingressing and egressing via a specific hardware queue, and avoids the potential
packet reordering that can occur when FANOUT_CPU is being used and irq affinity
varies.

Tested successfully by myself. applies to net-next

Signed-off-by: Neil Horman <[e-mail]>
CC: "David S. Miller" <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/uapi/linux/if_packet.h

···
 #define PACKET_FANOUT_CPU		2
 #define PACKET_FANOUT_ROLLOVER		3
 #define PACKET_FANOUT_RND		4
+#define PACKET_FANOUT_QM		5
 #define PACKET_FANOUT_FLAG_ROLLOVER	0x1000
 #define PACKET_FANOUT_FLAG_DEFRAG	0x8000
 

net/packet/af_packet.c

···
 	return idx;
 }
 
+static unsigned int fanout_demux_qm(struct packet_fanout *f,
+				    struct sk_buff *skb,
+				    unsigned int num)
+{
+	return skb_get_queue_mapping(skb) % num;
+}
+
 static bool fanout_has_flag(struct packet_fanout *f, u16 flag)
 {
 	return f->flags & (flag >> 8);
···
 		break;
 	case PACKET_FANOUT_RND:
 		idx = fanout_demux_rnd(f, skb, num);
+		break;
+	case PACKET_FANOUT_QM:
+		idx = fanout_demux_qm(f, skb, num);
 		break;
 	case PACKET_FANOUT_ROLLOVER:
 		idx = fanout_demux_rollover(f, skb, 0, (unsigned int) -1, num);
···
 	case PACKET_FANOUT_LB:
 	case PACKET_FANOUT_CPU:
 	case PACKET_FANOUT_RND:
+	case PACKET_FANOUT_QM:
 		break;
 	default:
 		return -EINVAL;