From: David Goulet <dgoulet@efficios.com>
Date: Tue, 25 Feb 2014 19:22:19 +0000 (-0500)
Subject: Fix: don't start session if no channel
X-Git-Tag: v2.3.2~5
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=1148bd3a82f9819f3e59b9ce2b3adc139de9db45;p=lttng-tools.git

Fix: don't start session if no channel

This adds a new error code that indicates that the session contains NO
channel.

Fixes #715

Signed-off-by: David Goulet <dgoulet@efficios.com>
---

diff --git a/include/lttng/lttng-error.h b/include/lttng/lttng-error.h
index 817cbe8f1..a94fcd697 100644
--- a/include/lttng/lttng-error.h
+++ b/include/lttng/lttng-error.h
@@ -102,7 +102,7 @@ enum lttng_error_code {
 	LTTNG_ERR_UST_CONSUMER32_FAIL    = 69,  /* 32-bit UST consumer start failed */
 	LTTNG_ERR_UST_STREAM_FAIL        = 70,  /* UST create stream failed */
 	LTTNG_ERR_SNAPSHOT_NODATA        = 71,  /* No data in snapshot. */
-	/* 72 */
+	LTTNG_ERR_NO_CHANNEL             = 72,  /* No channel found in the session. */
 	/* 73 */
 	LTTNG_ERR_UST_LIST_FAIL          = 74,  /* UST listing events failed */
 	LTTNG_ERR_UST_EVENT_EXIST        = 75,  /* UST event exist */
diff --git a/src/bin/lttng-sessiond/cmd.c b/src/bin/lttng-sessiond/cmd.c
index cca259923..2a61eee06 100644
--- a/src/bin/lttng-sessiond/cmd.c
+++ b/src/bin/lttng-sessiond/cmd.c
@@ -1583,6 +1583,7 @@ error:
 int cmd_start_trace(struct ltt_session *session)
 {
 	int ret;
+	unsigned long nb_chan = 0;
 	struct ltt_kernel_session *ksession;
 	struct ltt_ust_session *usess;
 
@@ -1598,6 +1599,21 @@ int cmd_start_trace(struct ltt_session *session)
 		goto error;
 	}
 
+	/*
+	 * Starting a session without channel is useless since after that it's not
+	 * possible to enable channel thus inform the client.
+	 */
+	if (usess && usess->domain_global.channels) {
+		nb_chan += lttng_ht_get_count(usess->domain_global.channels);
+	}
+	if (ksession) {
+		nb_chan += ksession->channel_count;
+	}
+	if (!nb_chan) {
+		ret = LTTNG_ERR_NO_CHANNEL;
+		goto error;
+	}
+
 	session->enabled = 1;
 
 	/* Kernel tracing */
diff --git a/src/common/error.c b/src/common/error.c
index 5020f316a..6c5aca65b 100644
--- a/src/common/error.c
+++ b/src/common/error.c
@@ -114,6 +114,7 @@ static const char *error_string_array[] = {
 	[ ERROR_INDEX(LTTNG_ERR_START_SESSION_ONCE) ] = "Session needs to be started once",
 	[ ERROR_INDEX(LTTNG_ERR_SNAPSHOT_FAIL) ] = "Snapshot record failed",
 	[ ERROR_INDEX(LTTNG_ERR_SNAPSHOT_NODATA) ] = "No data available in snapshot",
+	[ ERROR_INDEX(LTTNG_ERR_NO_CHANNEL) ] = "No channel found in the session",
 
 	/* Last element */
 	[ ERROR_INDEX(LTTNG_ERR_NR) ] = "Unknown error code"