From: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date: Tue, 18 Dec 2018 19:01:08 +0000 (-0500)
Subject: Fix: error logged on partial recvmsg() in MSG_DONTWAIT
X-Git-Url: http://git.efficios.com/?p=lttng-tools.git;a=commitdiff_plain;h=c2e8c3663b99ba900f4733696c70e7a5e32ae1a7

Fix: error logged on partial recvmsg() in MSG_DONTWAIT

The relay daemon logs a "Resource temporarily unavailable" error
message when the lttcomm_recvmsg_inet_sock() is invoked and
no data is left to be consumed from the lttcomm_sock.

The "recvmsg" socket operation is called in a loop by the relay
daemon to consume the data being received in 64k chunks. If, on
one of those iterations, 0 bytes are available, recvmsg() will
return an error (-1, errno = EAGAIN). This should not be
logged in non-blocking mode.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/src/common/sessiond-comm/inet.c b/src/common/sessiond-comm/inet.c
index ac450dbc8..57ffbe45c 100644
--- a/src/common/sessiond-comm/inet.c
+++ b/src/common/sessiond-comm/inet.c
@@ -381,6 +381,15 @@ ssize_t lttcomm_recvmsg_inet_sock(struct lttcomm_sock *sock, void *buf,
 	} while ((ret > 0 && ret < len_last) || (ret < 0 && errno == EINTR));
 
 	if (ret < 0) {
+		if (errno == EAGAIN && flags & MSG_DONTWAIT) {
+			/*
+			 * EAGAIN is expected in non-blocking mode and should
+			 * not be reported as an error. Moreover, if no data
+			 * was read, 0 must not be returned as it would be
+			 * interpreted as an orderly shutdown of the socket.
+			 */
+			goto end;
+		}
 		PERROR("recvmsg inet");
 	} else if (ret > 0) {
 		ret = len;