sessiond: enforce mmap output type for kernel metadata channel

A follow-up fix causes the consumer daemon to accumulate metadata
packets into a complete "unit" that can be parsed before sending it to
the relay daemon.

The consumer daemon will also need to extract the contents of the
metadata cache when computing a rotation position (follow-up fix too).

Hence, it is not possible to rely on the splice back-end as the
consumer daemon may need to accumulate more content than can be backed
by the ring buffer's underlying pages.

In both cases, the splice output mode could still be used when
combined with a memfd, but I see no tangible benefit. Moreover, it
would require a 3.17 kernel.

Curiously the kernel metadata channel configuration appears to be
hard-coded twice; once in the ltt_kernel_session's
ltt_kernel_metadata, and once again in
kernel_consumer_add_metadata(). kernel_consumer_add_metadata is
modified to use the kernel session's metadata configuration.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ia4cad82f595d3eee50d081851c234d4c2ef7ee5f

diff --git a/src/bin/lttng-sessiond/kernel-consumer.c b/src/bin/lttng-sessiond/kernel-consumer.c
index a086384aca782141b5ce8d162550880871b79547..17bf47d20bf1adf4e0000332f423fa8c250e848d 100644 (file)
--- a/src/bin/lttng-sessiond/kernel-consumer.c
+++ b/src/bin/lttng-sessiond/kernel-consumer.c
@@ -192,12 +192,15 @@ int kernel_consumer_add_metadata(struct consumer_socket *sock,
                        session->uid,
                        session->gid,
                        consumer->net_seq_index,
-                       DEFAULT_METADATA_NAME,
+                       session->metadata->conf->name,
                        1,
-                       DEFAULT_KERNEL_CHANNEL_OUTPUT,
+                       session->metadata->conf->attr.output,
                        CONSUMER_CHANNEL_TYPE_METADATA,
-                       0, 0,
-                       monitor, 0, session->is_live_session);
+                       session->metadata->conf->attr.tracefile_size,
+                       session->metadata->conf->attr.tracefile_count,
+                       monitor,
+                       session->metadata->conf->attr.live_timer_interval,
+                       session->is_live_session);
 
        health_code_update();
 

diff --git a/src/bin/lttng-sessiond/trace-kernel.c b/src/bin/lttng-sessiond/trace-kernel.c
index d1f826883538fe7c5cfeab19eefad1f5990cd400..d1c74a1ad370c5ddde8568d01b28579d13945cd0 100644 (file)
--- a/src/bin/lttng-sessiond/trace-kernel.c
+++ b/src/bin/lttng-sessiond/trace-kernel.c
@@ -385,6 +385,7 @@ error:
  */
 struct ltt_kernel_metadata *trace_kernel_create_metadata(void)
 {
+       int ret;
        struct ltt_kernel_metadata *lkm;
        struct lttng_channel *chan;
 
@@ -395,13 +396,38 @@ struct ltt_kernel_metadata *trace_kernel_create_metadata(void)
                goto error;
        }
 
+       ret = lttng_strncpy(
+                       chan->name, DEFAULT_METADATA_NAME, sizeof(chan->name));
+       if (ret) {
+               ERR("Failed to initialize metadata channel name to `%s`",
+                               DEFAULT_METADATA_NAME);
+               goto error;
+       }
+
        /* Set default attributes */
-       chan->attr.overwrite = DEFAULT_CHANNEL_OVERWRITE;
+       chan->attr.overwrite = DEFAULT_METADATA_OVERWRITE;
        chan->attr.subbuf_size = default_get_metadata_subbuf_size();
        chan->attr.num_subbuf = DEFAULT_METADATA_SUBBUF_NUM;
-       chan->attr.switch_timer_interval = DEFAULT_KERNEL_CHANNEL_SWITCH_TIMER;
-       chan->attr.read_timer_interval = DEFAULT_KERNEL_CHANNEL_READ_TIMER;
-       chan->attr.output = DEFAULT_KERNEL_CHANNEL_OUTPUT;
+       chan->attr.switch_timer_interval = DEFAULT_METADATA_SWITCH_TIMER;
+       chan->attr.read_timer_interval = DEFAULT_METADATA_READ_TIMER;;
+
+
+       /*
+        * The metadata channel of kernel sessions must use the "mmap"
+        * back-end since the consumer daemon accumulates complete
+        * metadata units before sending them to the relay daemon in
+        * live mode. The consumer daemon also needs to extract the contents
+        * of the metadata cache when computing a rotation position.
+        *
+        * In both cases, it is not possible to rely on the splice
+        * back-end as the consumer daemon may need to accumulate more
+        * content than can be backed by the ring buffer's underlying
+        * pages.
+        */
+       chan->attr.output = LTTNG_EVENT_MMAP;
+       chan->attr.tracefile_size = 0;
+       chan->attr.tracefile_count = 0;
+       chan->attr.live_timer_interval = 0;
 
        /* Init metadata */
        lkm->fd = -1;

diff --git a/src/common/defaults.h b/src/common/defaults.h
index f504f4d7834240cb35db840ae368da12e35c7ffe..08dea0213b9beb60a2d078849189cb7844a963d0 100644 (file)
--- a/src/common/defaults.h
+++ b/src/common/defaults.h
@@ -215,9 +215,10 @@
 #define DEFAULT_METADATA_SUBBUF_SIZE    CONFIG_DEFAULT_METADATA_SUBBUF_SIZE
 #define DEFAULT_METADATA_SUBBUF_NUM     CONFIG_DEFAULT_METADATA_SUBBUF_NUM
 #define DEFAULT_METADATA_CACHE_SIZE     CONFIG_DEFAULT_METADATA_CACHE_SIZE
-#define DEFAULT_METADATA_SWITCH_TIMER  CONFIG_DEFAULT_METADATA_SWITCH_TIMER
-#define DEFAULT_METADATA_READ_TIMER    CONFIG_DEFAULT_METADATA_READ_TIMER
-#define DEFAULT_METADATA_OUTPUT                        _DEFAULT_CHANNEL_OUTPUT
+#define DEFAULT_METADATA_SWITCH_TIMER  0
+#define DEFAULT_METADATA_READ_TIMER    0
+#define DEFAULT_METADATA_OVERWRITE     0
+#define DEFAULT_METADATA_OUTPUT                LTTNG_EVENT_MMAP
 
 /* Kernel has different defaults */
 

diff --git a/tests/unit/test_kernel_data.c b/tests/unit/test_kernel_data.c
index 6a35ea54a602489df1d35df9995a6f6cad5f8a14..857005923a93d7ccbdf27f423904a30533a164fd 100644 (file)
--- a/tests/unit/test_kernel_data.c
+++ b/tests/unit/test_kernel_data.c
@@ -95,17 +95,17 @@ static void test_create_kernel_metadata(void)
        ok(kern->metadata->fd == -1 &&
           kern->metadata->conf != NULL &&
           kern->metadata->conf->attr.overwrite
-                       == DEFAULT_CHANNEL_OVERWRITE &&
+                       == DEFAULT_METADATA_OVERWRITE &&
           kern->metadata->conf->attr.subbuf_size
                        == default_get_metadata_subbuf_size() &&
           kern->metadata->conf->attr.num_subbuf
                        == DEFAULT_METADATA_SUBBUF_NUM &&
           kern->metadata->conf->attr.switch_timer_interval
-                       == DEFAULT_KERNEL_CHANNEL_SWITCH_TIMER &&
+                       == DEFAULT_METADATA_SWITCH_TIMER &&
           kern->metadata->conf->attr.read_timer_interval
-                       == DEFAULT_KERNEL_CHANNEL_READ_TIMER &&
+                       == DEFAULT_METADATA_READ_TIMER &&
           kern->metadata->conf->attr.output
-              == DEFAULT_KERNEL_CHANNEL_OUTPUT,
+                       == LTTNG_EVENT_MMAP,
           "Validate kernel session metadata");
 
        trace_kernel_destroy_metadata(kern->metadata);