From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 20 Apr 2016 15:19:58 +0000 (-0400)
Subject: Allow channel mode override in snapshot sessions
X-Git-Tag: v2.9.0-rc1~121
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=8d5841ea483139d3ab2f2b4dd39263dad63832b1;p=lttng-tools.git

Allow channel mode override in snapshot sessions

Allow the lttng cmd line and liblttng-ctl users to override the channel
mode in snapshot sessions.

Note that liblttng-ctl users expecting that an "overwrite" mode
explicitly set at the value "0" (discard) for a snapshot session will
now create a channel in discard mode.

The DEFAULT_CHANNEL_OVERWRITE used by liblttng-ctl
lttng_channel_set_default_attr() is changed to "-1".

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---

diff --git a/include/lttng/channel.h b/include/lttng/channel.h
index 622ce85e9..732074c3a 100644
--- a/include/lttng/channel.h
+++ b/include/lttng/channel.h
@@ -33,7 +33,7 @@ extern "C" {
  */
 #define LTTNG_CHANNEL_ATTR_PADDING1        LTTNG_SYMBOL_NAME_LEN + 12
 struct lttng_channel_attr {
-	int overwrite;                      /* 1: overwrite, 0: discard */
+	int overwrite;                      /* -1: session default, 1: overwrite, 0: discard */
 	uint64_t subbuf_size;               /* bytes, power of 2 */
 	uint64_t num_subbuf;                /* power of 2 */
 	unsigned int switch_timer_interval; /* usec */
diff --git a/src/bin/lttng-sessiond/channel.c b/src/bin/lttng-sessiond/channel.c
index f35410e3a..88480c4b4 100644
--- a/src/bin/lttng-sessiond/channel.c
+++ b/src/bin/lttng-sessiond/channel.c
@@ -214,9 +214,16 @@ int channel_kernel_create(struct ltt_kernel_session *ksession,
 		attr = defattr;
 	}
 
+	/*
+	 * Set the overwrite mode for this channel based on the session
+	 * type unless the client explicitly overrides the channel mode.
+	 */
+	if (attr->attr.overwrite == DEFAULT_CHANNEL_OVERWRITE) {
+		attr->attr.overwrite = !!ksession->snapshot_mode;
+	}
+
+	/* Enforce mmap output for snapshot sessions. */
 	if (ksession->snapshot_mode) {
-		/* Force channel attribute for snapshot mode. */
-		attr->attr.overwrite = 1;
 		attr->attr.output = LTTNG_EVENT_MMAP;
 	}
 
@@ -318,9 +325,16 @@ int channel_ust_create(struct ltt_ust_session *usess,
 		}
 	}
 
+	/*
+	 * Set the overwrite mode for this channel based on the session
+	 * type unless the client explicitly overrides the channel mode.
+	 */
+	if (attr->attr.overwrite == DEFAULT_CHANNEL_OVERWRITE) {
+		attr->attr.overwrite = !!usess->snapshot_mode;
+	}
+
+	/* Enforce mmap output for snapshot sessions. */
 	if (usess->snapshot_mode) {
-		/* Force channel attribute for snapshot mode. */
-		attr->attr.overwrite = 1;
 		attr->attr.output = LTTNG_EVENT_MMAP;
 	}
 
diff --git a/src/bin/lttng/commands/create.c b/src/bin/lttng/commands/create.c
index 3379a3b27..0ae2b1096 100644
--- a/src/bin/lttng/commands/create.c
+++ b/src/bin/lttng/commands/create.c
@@ -439,7 +439,7 @@ static int create_session(void)
 			MSG("Default snapshot output set to: %s", print_str_url);
 		}
 		MSG("Snapshot mode set. Every channel enabled for that session will "
-				"be set in overwrite mode and mmap output.");
+				"be set to mmap output, and default to overwrite mode.");
 	}
 	if (opt_shm_path) {
 		MSG("Session %s set to shm_path: %s.", session_name,
diff --git a/src/common/defaults.h b/src/common/defaults.h
index 59fe8ec46..f05030766 100644
--- a/src/common/defaults.h
+++ b/src/common/defaults.h
@@ -188,7 +188,7 @@
 #define DEFAULT_PYTHON_EVENT_COMPONENT    "lttng_python"
 #define DEFAULT_PYTHON_EVENT_NAME         DEFAULT_PYTHON_EVENT_COMPONENT ":*"
 
-#define DEFAULT_CHANNEL_OVERWRITE       0
+#define DEFAULT_CHANNEL_OVERWRITE       -1
 #define DEFAULT_CHANNEL_TRACEFILE_SIZE  CONFIG_DEFAULT_CHANNEL_TRACEFILE_SIZE
 #define DEFAULT_CHANNEL_TRACEFILE_COUNT CONFIG_DEFAULT_CHANNEL_TRACEFILE_COUNT