netdev - [PATCH RFC net-next 1/6] sock: MSG_PEEK support for sk_error

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Date:   Wed, 17 Jan 2018 04:19:59 -0800
From:   Sowmini Varadhan <sowmini.varadhan@...cle.com>
To:     netdev@...r.kernel.org, willemdebruijn.kernel@...il.com
Cc:     davem@...emloft.net, rds-devel@....oracle.com,
        sowmini.varadhan@...cle.com, santosh.shilimkar@...cle.com
Subject: [PATCH RFC net-next 1/6] sock: MSG_PEEK support for sk_error_queue

Allow the application the ability to use MSG_PEEK with sk_error_queue
so that it can peek and re-read message in cases where MSG_TRUNC
may be encountered.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
---
 drivers/net/tun.c      |    2 +-
 include/net/sock.h     |    2 +-
 net/core/sock.c        |    7 +++++--
 net/packet/af_packet.c |    3 ++-
 4 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 2fba3be..cfd0e0f 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2313,7 +2313,7 @@ static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len,
 	}
 	if (flags & MSG_ERRQUEUE) {
 		ret = sock_recv_errqueue(sock->sk, m, total_len,
-					 SOL_PACKET, TUN_TX_TIMESTAMP);
+					 SOL_PACKET, TUN_TX_TIMESTAMP, flags);
 		goto out;
 	}
 	ret = tun_do_read(tun, tfile, &m->msg_iter, flags & MSG_DONTWAIT, ptr);
diff --git a/include/net/sock.h b/include/net/sock.h
index 73b7830..f0b6990 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2343,7 +2343,7 @@ static inline bool sk_listener(const struct sock *sk)
 int sock_get_timestamp(struct sock *, struct timeval __user *);
 int sock_get_timestampns(struct sock *, struct timespec __user *);
 int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len, int level,
-		       int type);
+		       int type, int flags);
 
 bool sk_ns_capable(const struct sock *sk,
 		   struct user_namespace *user_ns, int cap);
diff --git a/net/core/sock.c b/net/core/sock.c
index 72d14b2..4f52677 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2887,7 +2887,7 @@ void sock_enable_timestamp(struct sock *sk, int flag)
 }
 
 int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len,
-		       int level, int type)
+		       int level, int type, int flags)
 {
 	struct sock_exterr_skb *serr;
 	struct sk_buff *skb;
@@ -2916,7 +2916,10 @@ int sock_recv_errqueue(struct sock *sk, struct msghdr *msg, int len,
 	err = copied;
 
 out_free_skb:
-	kfree_skb(skb);
+	if (likely(!(flags & MSG_PEEK)))
+		kfree_skb(skb);
+	else
+		skb_queue_head(&sk->sk_error_queue, skb);
 out:
 	return err;
 }
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index ee7aa0b..4314f31 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -3294,7 +3294,8 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 
 	if (flags & MSG_ERRQUEUE) {
 		err = sock_recv_errqueue(sk, msg, len,
-					 SOL_PACKET, PACKET_TX_TIMESTAMP);
+					 SOL_PACKET, PACKET_TX_TIMESTAMP,
+					 flags);
 		goto out;
 	}
 
-- 
1.7.1