Re: [PATCH] Generalize socket rx gap / receive queue overflow cmsg (v4)

[Neil Horman <nhorman@tuxdriver.com>]

Version 4

Change Notes:

1) Remove the superfolous put_cmsg that I missed in the last version

=======================================================================

Create a new socket level option to report number of queue overflows

Recently I augmented the AF_PACKET protocol to report the number of frames lost
on the socket receive queue between any two enqueued frames.  This value was
exported via a SOL_PACKET level cmsg.  AFter I completed that work it was
requested that this feature be generalized so that any datagram oriented socket
could make use of this option.  As such I've created this patch, It creates a
new SOL_SOCKET level option called SO_RXQ_OVFL, which when enabled exports a
SOL_SOCKET level cmsg that reports the nubmer of times the sk_receive_queue
overflowed between any two given frames.  It also augments the AF_PACKET
protocol to take advantage of this new feature (as it previously did not touch
sk->sk_drops, which this patch uses to record the overflow count).  Tested
successfully by me.

Notes:

1) Unlike my previous patch, this patch simply records the sk_drops value, which
is not a number of drops between packets, but rather a total number of drops.
Deltas must be computed in user space.

2) While this patch currently works with datagram oriented protocols, it will
also be accepted by non-datagram oriented protocols. I'm not sure if thats
agreeable to everyone, but my argument in favor of doing so is that, for those
protocols which aren't applicable to this option, sk_drops will always be zero,
and reporting no drops on a receive queue that isn't used for those
non-participating protocols seems reasonable to me.  This also saves us having
to code in a per-protocol opt in mechanism.

3) This applies cleanly to net-next assuming that commit
977750076d98c7ff6cbda51858bb5a5894a9d9ab (my af packet cmsg patch) is reverted

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>

diff --git a/include/asm-generic/socket.h b/include/asm-generic/socket.h
index 538991c..9a6115e 100644
--- a/include/asm-generic/socket.h
+++ b/include/asm-generic/socket.h
@@ -63,4 +63,5 @@
 #define SO_PROTOCOL		38
 #define SO_DOMAIN		39
 
+#define SO_RXQ_OVFL             40
 #endif /* __ASM_GENERIC_SOCKET_H */
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -389,8 +389,10 @@
 #ifdef CONFIG_NETWORK_SECMARK
 	__u32			secmark;
 #endif
-
-	__u32			mark;
+	union {
+		__u32		mark;
+		__u32		dropcount;
+	};
 
 	__u16			vlan_tci;
 
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -505,6 +505,7 @@
 	SOCK_TIMESTAMPING_RAW_HARDWARE, /* %SOF_TIMESTAMPING_RAW_HARDWARE */
 	SOCK_TIMESTAMPING_SYS_HARDWARE, /* %SOF_TIMESTAMPING_SYS_HARDWARE */
 	SOCK_FASYNC, /* fasync() active */
+	SOCK_RXQ_OVFL,
 };
 
 static inline void sock_copy_flags(struct sock *nsk, struct sock *osk)
@@ -1493,6 +1494,8 @@
 		sk->sk_stamp = kt;
 }
 
+extern void sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk, struct sk_buff *skb);
+
 /**
  * sock_tx_timestamp - checks whether the outgoing packet is to be time stamped
  * @msg:	outgoing packet
--- a/net/atm/common.c
+++ b/net/atm/common.c
@@ -496,7 +496,7 @@
 	error = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
 	if (error)
 		return error;
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 	pr_debug("RcvM %d -= %d\n", atomic_read(&sk->sk_rmem_alloc), skb->truesize);
 	atm_return(vcc, skb->truesize);
 	skb_free_datagram(sk, skb);
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -257,7 +257,7 @@
 	skb_reset_transport_header(skb);
 	err = skb_copy_datagram_iovec(skb, 0, msg->msg_iov, copied);
 	if (err == 0)
-		sock_recv_timestamp(msg, sk, skb);
+		sock_recv_ts_and_drops(msg, sk, skb);
 
 	skb_free_datagram(sk, skb);
 
--- a/net/bluetooth/rfcomm/sock.c
+++ b/net/bluetooth/rfcomm/sock.c
@@ -703,7 +703,7 @@
 		copied += chunk;
 		size   -= chunk;
 
-		sock_recv_timestamp(msg, sk, skb);
+		sock_recv_ts_and_drops(msg, sk, skb);
 
 		if (!(flags & MSG_PEEK)) {
 			atomic_sub(chunk, &sk->sk_rmem_alloc);
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1534,7 +1534,7 @@
 		return err;
 	}
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	if (msg->msg_name) {
 		msg->msg_namelen = sizeof(struct sockaddr_can);
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -702,7 +702,7 @@
 		return err;
 	}
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	if (msg->msg_name) {
 		msg->msg_namelen = sizeof(struct sockaddr_can);
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -276,6 +276,8 @@
 {
 	int err = 0;
 	int skb_len;
+	unsigned long flags;
+	struct sk_buff_head *list = &sk->sk_receive_queue;
 
 	/* Cast sk->rcvbuf to unsigned... It's pointless, but reduces
 	   number of warnings when compiling with -W --ANK
@@ -305,7 +307,10 @@
 	 */
 	skb_len = skb->len;
 
-	skb_queue_tail(&sk->sk_receive_queue, skb);
+	spin_lock_irqsave(&list->lock, flags);
+	skb->dropcount = atomic_read(&sk->sk_drops);
+	__skb_queue_tail(list, skb);
+	spin_unlock_irqrestore(&list->lock, flags);
 
 	if (!sock_flag(sk, SOCK_DEAD))
 		sk->sk_data_ready(sk, skb_len);
@@ -702,6 +707,12 @@
 
 		/* We implement the SO_SNDLOWAT etc to
 		   not be settable (1003.1g 5.3) */
+	case SO_RXQ_OVFL:
+		if (valbool)
+			sock_set_flag(sk, SOCK_RXQ_OVFL);
+		else
+			sock_reset_flag(sk, SOCK_RXQ_OVFL);
+		break;
 	default:
 		ret = -ENOPROTOOPT;
 		break;
@@ -901,6 +912,10 @@
 		v.val = sk->sk_mark;
 		break;
 
+	case SO_RXQ_OVFL:
+		v.val = !!sock_flag(sk, SOCK_RXQ_OVFL);
+		break;
+
 	default:
 		return -ENOPROTOOPT;
 	}
--- a/net/ieee802154/dgram.c
+++ b/net/ieee802154/dgram.c
@@ -303,7 +303,7 @@
 	if (err)
 		goto done;
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	if (flags & MSG_TRUNC)
 		copied = skb->len;
--- a/net/ieee802154/raw.c
+++ b/net/ieee802154/raw.c
@@ -191,7 +191,7 @@
 	if (err)
 		goto done;
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	if (flags & MSG_TRUNC)
 		copied = skb->len;
--- a/net/ipv4/raw.c
+++ b/net/ipv4/raw.c
@@ -682,7 +682,7 @@
 	if (err)
 		goto done;
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	/* Copy the address. */
 	if (sin) {
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -951,7 +951,7 @@
 		UDP_INC_STATS_USER(sock_net(sk),
 				UDP_MIB_INDATAGRAMS, is_udplite);
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	/* Copy the address. */
 	if (sin) {
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -497,7 +497,7 @@
 			sin6->sin6_scope_id = IP6CB(skb)->iif;
 	}
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	if (np->rxopt.all)
 		datagram_recv_ctl(sk, msg, skb);
--- a/net/ipv6/udp.c
+++ b/net/ipv6/udp.c
@@ -252,7 +252,7 @@
 					UDP_MIB_INDATAGRAMS, is_udplite);
 	}
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	/* Copy the address. */
 	if (msg->msg_name) {
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -3606,7 +3606,7 @@
 	if (err)
 		goto out_free;
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	err = (flags & MSG_TRUNC) ? skb->len : copied;
 
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -627,15 +627,14 @@
 
 	spin_lock(&sk->sk_receive_queue.lock);
 	po->stats.tp_packets++;
+	skb->dropcount = atomic_read(&sk->sk_drops);
 	__skb_queue_tail(&sk->sk_receive_queue, skb);
 	spin_unlock(&sk->sk_receive_queue.lock);
 	sk->sk_data_ready(sk, skb->len);
 	return 0;
 
 drop_n_acct:
-	spin_lock(&sk->sk_receive_queue.lock);
-	po->stats.tp_drops++;
-	spin_unlock(&sk->sk_receive_queue.lock);
+	po->stats.tp_drops = atomic_inc_return(&sk->sk_drops);
 
 drop_n_restore:
 	if (skb_head != skb->data && skb_shared(skb)) {
@@ -1478,7 +1477,7 @@
 	if (err)
 		goto out_free;
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 
 	if (msg->msg_name)
 		memcpy(msg->msg_name, &PACKET_SKB_CB(skb)->sa,
--- a/net/rxrpc/ar-recvmsg.c
+++ b/net/rxrpc/ar-recvmsg.c
@@ -146,7 +146,7 @@
 				memcpy(msg->msg_name,
 				       &call->conn->trans->peer->srx,
 				       sizeof(call->conn->trans->peer->srx));
-			sock_recv_timestamp(msg, &rx->sk, skb);
+			sock_recv_ts_and_drops(msg, &rx->sk, skb);
 		}
 
 		/* receive the message */
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -1958,7 +1958,7 @@
 	if (err)
 		goto out_free;
 
-	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_ts_and_drops(msg, sk, skb);
 	if (sctp_ulpevent_is_notification(event)) {
 		msg->msg_flags |= MSG_NOTIFICATION;
 		sp->pf->event_msgname(event, msg->msg_name, addr_len);
--- a/net/socket.c
+++ b/net/socket.c
@@ -668,6 +668,21 @@
 
 EXPORT_SYMBOL_GPL(__sock_recv_timestamp);
 
+inline void sock_recv_drops(struct msghdr *msg, struct sock *sk, struct sk_buff *skb)
+{
+	if (sock_flag(sk, SOCK_RXQ_OVFL) && skb && skb->dropcount)
+		put_cmsg(msg, SOL_SOCKET, SO_RXQ_OVFL,
+			sizeof(__u32), &skb->dropcount);
+}
+
+void sock_recv_ts_and_drops(struct msghdr *msg, struct sock *sk,
+	struct sk_buff *skb)
+{
+	sock_recv_timestamp(msg, sk, skb);
+	sock_recv_drops(msg, sk, skb);
+}
+EXPORT_SYMBOL_GPL(sock_recv_ts_and_drops);
+
 static inline int __sock_recvmsg(struct kiocb *iocb, struct socket *sock,
 				 struct msghdr *msg, size_t size, int flags)
 {