From: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Date: Thu, 9 Jul 2020 18:57:57 +0000 (-0400)
Subject: Fix: partial recv lead to client disconnect
X-Git-Tag: v2.12.2~10
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=2f31577d1c07af4e7ea28fd72beea4bf3959fa57;p=lttng-tools.git

Fix: partial recv lead to client disconnect

On EWOULDBLOCK and EAGAIN, the ret value from
`lttcomm_send_unix_sock_non_block` and
`lttcomm_recv_unix_sock_non_block` would be equal to -1.

Solution
=====

For such cases, set ret equal to zero since it is effectively what was
received/sent. Caller should treat ret  >= 0 as `success` anyway.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I47677f26850bf544f672d270972de7cc2c6a2817
---

diff --git a/src/bin/lttng-sessiond/notification-thread-events.c b/src/bin/lttng-sessiond/notification-thread-events.c
index 6c69a0232..9660f9aad 100644
--- a/src/bin/lttng-sessiond/notification-thread-events.c
+++ b/src/bin/lttng-sessiond/notification-thread-events.c
@@ -2564,8 +2564,7 @@ int client_flush_outgoing_queue(struct notification_client *client,
 	ret = lttcomm_send_unix_sock_non_block(client->socket,
 			client->communication.outbound.buffer.data,
 			to_send_count);
-	if ((ret < 0 && (errno == EAGAIN || errno == EWOULDBLOCK)) ||
-			(ret > 0 && ret < to_send_count)) {
+	if ((ret >= 0 && ret < to_send_count)) {
 		DBG("[notification-thread] Client (socket fd = %i) outgoing queue could not be completely flushed",
 				client->socket);
 		to_send_count -= max(ret, 0);
diff --git a/src/common/unix.c b/src/common/unix.c
index 26eda52d9..df92b7a06 100644
--- a/src/common/unix.c
+++ b/src/common/unix.c
@@ -210,6 +210,9 @@ ssize_t lttcomm_recv_unix_sock(int sock, void *buf, size_t len)
  * Receive data of size len in put that data into the buf param. Using recvmsg
  * API. Only use with sockets set in non-blocking mode.
  *
+ * NOTE: EPIPE errors are NOT reported. This call expects the socket to be in a
+ * poll set. The poll loop will handle the EPIPE original cause.
+ *
  * Return the size of received data.
  */
 LTTNG_HIDDEN
@@ -232,11 +235,21 @@ retry:
 		if (errno == EINTR) {
 			goto retry;
 		} else {
-			/* We consider EPIPE and EAGAIN as expected. */
-			if (!lttng_opt_quiet &&
-					(errno != EPIPE && errno != EAGAIN)) {
-				PERROR("recvmsg");
+			/*
+			 * We consider EPIPE and EAGAIN/EWOULDBLOCK as expected.
+			 */
+			if (errno == EAGAIN || errno == EWOULDBLOCK ||
+					errno == EPIPE) {
+				/*
+				 * Nothing was recv.
+				 */
+				ret = 0;
+				goto end;
 			}
+
+			/* Unexpected error */
+			PERROR("recvmsg");
+			ret = -1;
 			goto end;
 		}
 	}
@@ -295,6 +308,9 @@ end:
  * of the function is that this one does not retry to send on partial sends,
  * except if the interruption was caused by a signal (EINTR).
  *
+ * NOTE: EPIPE errors are NOT reported. This call expects the socket to be in a
+ * poll set. The poll loop will handle the EPIPE original cause.
+ *
  * Return the size of sent data.
  */
 LTTNG_HIDDEN
@@ -317,11 +333,22 @@ retry:
 		if (errno == EINTR) {
 			goto retry;
 		} else {
-			/* We consider EPIPE and EAGAIN as expected. */
-			if (!lttng_opt_quiet &&
-					(errno != EPIPE && errno != EAGAIN)) {
-				PERROR("sendmsg");
+			/*
+			 * We consider EPIPE and EAGAIN/EWOULDBLOCK as expected.
+			 */
+			if (errno == EAGAIN || errno == EWOULDBLOCK ||
+					errno == EPIPE) {
+				/*
+				 * This can happen in non blocking mode.
+				 * Nothing was sent.
+				 */
+				ret = 0;
+				goto end;
 			}
+
+			/* Unexpected error */
+			PERROR("sendmsg");
+			ret = -1;
 			goto end;
 		}
 	}