Re: [tipc-discussion] [PATCHv2 net-next] tipc: keep the skb in rcv queue until the whole data is read

[maloy <ma...@do...>]

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-------- Original message --------From: Xin Long <luc...@gm...> Date: 2021-06-30  20:21  (GMT-05:00) To: Jon Maloy <jm...@re...>, Erin Shepherd <eri...@e4...>, tip...@li... Subject: [tipc-discussion] [PATCHv2 net-next] tipc: keep the skb in rcv
  queue until the whole data is read Currently, when userspace reads a datagram with a buffer that issmaller than this datagram, the data will be truncated and onlypart of it can be received by users. It doesn't seem right thatusers don't know the datagram size and have to use a huge bufferto read it to avoid the truncation.This patch to fix it by keeping the skb in rcv queue until thewhole data is read by users. Only the last msg of the datagramwill be marked with MSG_EOR, just as TCP/SCTP does.Note that this will work as above only when MSG_EOR is set in theflags parameter of recvmsg(), so that it won't break any old userapplications.v1->v2:  - To enable this only when the flags with MSG_EOR is passed into    recvmsg() to fix the compatibility isssue as Erin noticed.Signed-off-by: Xin Long <luc...@gm...>--- net/tipc/socket.c | 36 +++++++++++++++++++++++++++--------- 1 file changed, 27 insertions(+), 9 deletions(-)diff --git a/net/tipc/socket.c b/net/tipc/socket.cindex 34a97ea36cc8..9b0b311c7ec1 100644--- a/net/tipc/socket.c+++ b/net/tipc/socket.c@@ -1880,6 +1880,7 @@ static int tipc_recvmsg(struct socket *sock, struct msghdr *m, 	bool connected = !tipc_sk_type_connectionless(sk); 	struct tipc_sock *tsk = tipc_sk(sk); 	int rc, err, hlen, dlen, copy;+	struct tipc_skb_cb *skb_cb; 	struct sk_buff_head xmitq; 	struct tipc_msg *hdr; 	struct sk_buff *skb;@@ -1903,6 +1904,7 @@ static int tipc_recvmsg(struct socket *sock, struct msghdr *m, 		if (unlikely(rc)) 			goto exit; 		skb = skb_peek(&sk->sk_receive_queue);+		skb_cb = TIPC_SKB_CB(skb); 		hdr = buf_msg(skb); 		dlen = msg_data_sz(hdr); 		hlen = msg_hdr_sz(hdr);@@ -1922,18 +1924,33 @@ static int tipc_recvmsg(struct socket *sock, struct msghdr *m,  	/* Capture data if non-error msg, otherwise just set return value */ 	if (likely(!err)) {-		copy = min_t(int, dlen, buflen);-		if (unlikely(copy != dlen))-			m->msg_flags |= MSG_TRUNC;-		rc = skb_copy_datagram_msg(skb, hlen, m, copy);+		int offset = skb_cb->bytes_read;++		copy = min_t(int, dlen - offset, buflen);+		rc = skb_copy_datagram_msg(skb, hlen + offset, m, copy);+		if (unlikely(rc))+			goto exit;+		if (unlikely(offset + copy < dlen)) {+			if (flags & MSG_EOR) {+				if (!(flags & MSG_PEEK))+					skb_cb->bytes_read = offset + copy;+			} else {+				m->msg_flags |= MSG_TRUNC;+				skb_cb->bytes_read = 0;+			}+		} else {+			if (flags & MSG_EOR)+				m->msg_flags |= MSG_EOR;+			skb_cb->bytes_read = 0;+		} 	} else { 		copy = 0; 		rc = 0;-		if (err != TIPC_CONN_SHUTDOWN && connected && !m->msg_control)+		if (err != TIPC_CONN_SHUTDOWN && connected && !m->msg_control) { 			rc = -ECONNRESET;+			goto exit;+		} 	}-	if (unlikely(rc))-		goto exit;  	/* Mark message as group event if applicable */ 	if (unlikely(grp_evt)) {@@ -1956,9 +1973,10 @@ static int tipc_recvmsg(struct socket *sock, struct msghdr *m, 		tipc_node_distr_xmit(sock_net(sk), &xmitq); 	} -	tsk_advance_rx_queue(sk);+	if (!skb_cb->bytes_read)+		tsk_advance_rx_queue(sk); -	if (likely(!connected))+	if (likely(!connected) || skb_cb->bytes_read) 		goto exit;  	/* Send connection flow control advertisement when applicable */-- 2.27.0Signed-off-by: Jon Maloy <jm...@re...>_______________________________________________tipc-discussion mailing lis...@li...https://lists.sourceforge.net/lists/listinfo/tipc-discussion