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 57c8f549feac41918930165156bef72bb45f5ed2..a3295e9279923bb43141a5e2af75b3133717b5de 100644 (file)
--- a/src/bin/lttng-sessiond/kernel-consumer.c
+++ b/src/bin/lttng-sessiond/kernel-consumer.c
@@ -228,12 +228,23 @@ int kernel_consumer_add_metadata(struct consumer_socket *sock,
        consumer = ksession->consumer;
 
        /* Prep channel message structure */
-       consumer_init_add_channel_comm_msg(&lkm, ksession->metadata->key,
-                       ksession->id, "", ksession->uid, ksession->gid,
-                       consumer->net_seq_index, DEFAULT_METADATA_NAME, 1,
-                       DEFAULT_KERNEL_CHANNEL_OUTPUT,
-                       CONSUMER_CHANNEL_TYPE_METADATA, 0, 0, monitor, 0,
-                       ksession->is_live_session, 0,
+       consumer_init_add_channel_comm_msg(&lkm,
+                       ksession->metadata->key,
+                       ksession->id,
+                       "",
+                       ksession->uid,
+                       ksession->gid,
+                       consumer->net_seq_index,
+                       ksession->metadata->conf->name,
+                       1,
+                       ksession->metadata->conf->attr.output,
+                       CONSUMER_CHANNEL_TYPE_METADATA,
+                       ksession->metadata->conf->attr.tracefile_size,
+                       ksession->metadata->conf->attr.tracefile_count,
+                       monitor,
+                       ksession->metadata->conf->attr.live_timer_interval,
+                       ksession->is_live_session,
+                       0,
                        ksession->current_trace_chunk);
 
        health_code_update();

diff --git a/src/bin/lttng-sessiond/kernel.c b/src/bin/lttng-sessiond/kernel.c
index 5fc6ae43726ae08d8b282f6ebb40e80520d2f74c..cff8fb25bab198a831a4c5678552dddacbb1386d 100644 (file)
--- a/src/bin/lttng-sessiond/kernel.c
+++ b/src/bin/lttng-sessiond/kernel.c
@@ -16,6 +16,7 @@
  */
 
 #define _LGPL_SOURCE
+
 #include <fcntl.h>
 #include <stdlib.h>
 #include <stdio.h>

diff --git a/src/bin/lttng-sessiond/trace-kernel.c b/src/bin/lttng-sessiond/trace-kernel.c
index e0491c95b3fba9112b95f33bafb78550e3b04e49..0c472c00f9188677743aac78e266ab1e786a297c 100644 (file)
--- a/src/bin/lttng-sessiond/trace-kernel.c
+++ b/src/bin/lttng-sessiond/trace-kernel.c
@@ -29,6 +29,7 @@
 #include <common/common.h>
 #include <common/defaults.h>
 #include <common/trace-chunk.h>
+#include <common/macros.h>
 
 #include "consumer.h"
 #include "trace-kernel.h"
@@ -465,6 +466,7 @@ error:
  */
 struct ltt_kernel_metadata *trace_kernel_create_metadata(void)
 {
+       int ret;
        struct ltt_kernel_metadata *lkm;
        struct lttng_channel *chan;
 
@@ -475,13 +477,38 @@ 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 183e315183356c1ebca2f5a8d4f65beea7dbc1b2..78ac2c2d8711ea547ad076c6b70a99f4365a5fe8 100644 (file)
--- a/src/common/defaults.h
+++ b/src/common/defaults.h
@@ -205,9 +205,10 @@
 #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 fe60622360a689d2c61926cf0bf347d4d631c959..a6c99c858c892cad0cec232bff87b319ec4033ab 100644 (file)
--- a/tests/unit/test_kernel_data.c
+++ b/tests/unit/test_kernel_data.c
@@ -92,17 +92,17 @@ 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);