Clarify kernel version check error messages
[lttng-tools.git] / src / bin / lttng-sessiond / kernel.c
index dd815c44536fd8629d01537d6a6d749f70033147..dee065460b1e661f8dca9f32a9070f3b876b24bc 100644 (file)
  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  */
 
-#define _GNU_SOURCE
+#define _LGPL_SOURCE
 #include <errno.h>
 #include <fcntl.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
+#include <inttypes.h>
 
 #include <common/common.h>
 #include <common/kernel-ctl/kernel-ctl.h>
+#include <common/kernel-ctl/kernel-ioctl.h>
 #include <common/sessiond-comm/sessiond-comm.h>
 
+#include "consumer.h"
 #include "kernel.h"
+#include "kernel-consumer.h"
 #include "kern-modules.h"
+#include "utils.h"
 
 /*
  * Add context on a kernel channel.
  */
 int kernel_add_channel_context(struct ltt_kernel_channel *chan,
-               struct lttng_kernel_context *ctx)
+               struct ltt_kernel_context *ctx)
 {
        int ret;
 
+       assert(chan);
+       assert(ctx);
+
        DBG("Adding context to channel %s", chan->channel->name);
-       ret = kernctl_add_context(chan->fd, ctx);
+       ret = kernctl_add_context(chan->fd, &ctx->ctx);
        if (ret < 0) {
-               if (errno != EEXIST) {
-                       PERROR("add context ioctl");
-               } else {
+               switch (errno) {
+               case ENOSYS:
+                       /* Exists but not available for this kernel */
+                       ret = LTTNG_ERR_KERN_CONTEXT_UNAVAILABLE;
+                       goto error;
+               case EEXIST:
                        /* If EEXIST, we just ignore the error */
                        ret = 0;
+                       goto end;
+               default:
+                       PERROR("add context ioctl");
+                       ret = LTTNG_ERR_KERN_CONTEXT_FAIL;
+                       goto error;
                }
-               goto error;
-       }
-
-       chan->ctx = zmalloc(sizeof(struct lttng_kernel_context));
-       if (chan->ctx == NULL) {
-               PERROR("zmalloc event context");
-               goto error;
-       }
-
-       memcpy(chan->ctx, ctx, sizeof(struct lttng_kernel_context));
-
-       return 0;
-
-error:
-       return ret;
-}
-
-/*
- * Add context on a kernel event.
- */
-int kernel_add_event_context(struct ltt_kernel_event *event,
-               struct lttng_kernel_context *ctx)
-{
-       int ret;
-
-       DBG("Adding context to event %s", event->event->name);
-       ret = kernctl_add_context(event->fd, ctx);
-       if (ret < 0) {
-               PERROR("add context ioctl");
-               goto error;
        }
 
-       event->ctx = zmalloc(sizeof(struct lttng_kernel_context));
-       if (event->ctx == NULL) {
-               PERROR("zmalloc event context");
-               goto error;
-       }
-
-       memcpy(event->ctx, ctx, sizeof(struct lttng_kernel_context));
-
+end:
+       cds_list_add_tail(&ctx->list, &chan->ctx_list);
        return 0;
 
 error:
@@ -102,8 +82,10 @@ int kernel_create_session(struct ltt_session *session, int tracer_fd)
        int ret;
        struct ltt_kernel_session *lks;
 
+       assert(session);
+
        /* Allocate data structure */
-       lks = trace_kernel_create_session(session->path);
+       lks = trace_kernel_create_session();
        if (lks == NULL) {
                ret = -1;
                goto error;
@@ -123,6 +105,7 @@ int kernel_create_session(struct ltt_session *session, int tracer_fd)
                PERROR("fcntl session fd");
        }
 
+       lks->id = session->id;
        lks->consumer_fds_sent = 0;
        session->kernel_session = lks;
 
@@ -131,6 +114,9 @@ int kernel_create_session(struct ltt_session *session, int tracer_fd)
        return 0;
 
 error:
+       if (lks) {
+               trace_kernel_destroy_session(lks);
+       }
        return ret;
 }
 
@@ -139,17 +125,26 @@ error:
  * kernel session.
  */
 int kernel_create_channel(struct ltt_kernel_session *session,
-               struct lttng_channel *chan, char *path)
+               struct lttng_channel *chan)
 {
        int ret;
        struct ltt_kernel_channel *lkc;
 
+       assert(session);
+       assert(chan);
+
        /* Allocate kernel channel */
-       lkc = trace_kernel_create_channel(chan, path);
+       lkc = trace_kernel_create_channel(chan);
        if (lkc == NULL) {
                goto error;
        }
 
+       DBG3("Kernel create channel %s with attr: %d, %" PRIu64 ", %" PRIu64 ", %u, %u, %d, %d",
+                       chan->name, lkc->channel->attr.overwrite,
+                       lkc->channel->attr.subbuf_size, lkc->channel->attr.num_subbuf,
+                       lkc->channel->attr.switch_timer_interval, lkc->channel->attr.read_timer_interval,
+                       lkc->channel->attr.live_timer_interval, lkc->channel->attr.output);
+
        /* Kernel tracer channel creation */
        ret = kernctl_create_channel(session->fd, &lkc->channel->attr);
        if (ret < 0) {
@@ -168,27 +163,39 @@ int kernel_create_channel(struct ltt_kernel_session *session,
        /* Add channel to session */
        cds_list_add(&lkc->list, &session->channel_list.head);
        session->channel_count++;
+       lkc->session = session;
 
-       DBG("Kernel channel %s created (fd: %d and path: %s)",
-                       lkc->channel->name, lkc->fd, lkc->pathname);
+       DBG("Kernel channel %s created (fd: %d)", lkc->channel->name, lkc->fd);
 
        return 0;
 
 error:
+       if (lkc) {
+               free(lkc->channel);
+               free(lkc);
+       }
        return -1;
 }
 
 /*
  * Create a kernel event, enable it to the kernel tracer and add it to the
  * channel event list of the kernel session.
+ * We own filter_expression and filter.
  */
 int kernel_create_event(struct lttng_event *ev,
-               struct ltt_kernel_channel *channel)
+               struct ltt_kernel_channel *channel,
+               char *filter_expression,
+               struct lttng_filter_bytecode *filter)
 {
        int ret;
        struct ltt_kernel_event *event;
 
-       event = trace_kernel_create_event(ev);
+       assert(ev);
+       assert(channel);
+
+       /* We pass ownership of filter_expression and filter */
+       event = trace_kernel_create_event(ev, filter_expression,
+                       filter);
        if (event == NULL) {
                ret = -1;
                goto error;
@@ -196,26 +203,23 @@ int kernel_create_event(struct lttng_event *ev,
 
        ret = kernctl_create_event(channel->fd, event->event);
        if (ret < 0) {
-               if (errno != EEXIST) {
+               switch (errno) {
+               case EEXIST:
+                       break;
+               case ENOSYS:
+                       WARN("Event type not implemented");
+                       break;
+               case ENOENT:
+                       WARN("Event %s not found!", ev->name);
+                       break;
+               default:
                        PERROR("create event ioctl");
                }
                ret = -errno;
                goto free_event;
        }
 
-       /*
-        * LTTNG_KERNEL_SYSCALL event creation will return 0 on success.
-        */
-       if (ret == 0 && event->event->instrumentation == LTTNG_KERNEL_SYSCALL) {
-               DBG2("Kernel event syscall creation success");
-               /*
-                * We use fd == -1 to ensure that we never trigger a close of fd
-                * 0.
-                */
-               event->fd = -1;
-               goto add_list;
-       }
-
+       event->type = ev->type;
        event->fd = ret;
        /* Prevent fd duplication after execlp() */
        ret = fcntl(event->fd, F_SETFD, FD_CLOEXEC);
@@ -223,7 +227,26 @@ int kernel_create_event(struct lttng_event *ev,
                PERROR("fcntl session fd");
        }
 
-add_list:
+       if (filter) {
+               ret = kernctl_filter(event->fd, filter);
+               if (ret) {
+                       goto filter_error;
+               }
+       }
+
+       ret = kernctl_enable(event->fd);
+       if (ret < 0) {
+               switch (errno) {
+               case EEXIST:
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
+                       break;
+               default:
+                       PERROR("enable kernel event");
+                       break;
+               }
+               goto enable_error;
+       }
+
        /* Add event to event list */
        cds_list_add(&event->list, &channel->events_list.head);
        channel->event_count++;
@@ -232,6 +255,16 @@ add_list:
 
        return 0;
 
+enable_error:
+filter_error:
+       {
+               int closeret;
+
+               closeret = close(event->fd);
+               if (closeret) {
+                       PERROR("close event fd");
+               }
+       }
 free_event:
        free(event);
 error:
@@ -245,6 +278,8 @@ int kernel_disable_channel(struct ltt_kernel_channel *chan)
 {
        int ret;
 
+       assert(chan);
+
        ret = kernctl_disable(chan->fd);
        if (ret < 0) {
                PERROR("disable chan ioctl");
@@ -268,6 +303,8 @@ int kernel_enable_channel(struct ltt_kernel_channel *chan)
 {
        int ret;
 
+       assert(chan);
+
        ret = kernctl_enable(chan->fd);
        if (ret < 0 && errno != EEXIST) {
                PERROR("Enable kernel chan");
@@ -290,11 +327,13 @@ int kernel_enable_event(struct ltt_kernel_event *event)
 {
        int ret;
 
+       assert(event);
+
        ret = kernctl_enable(event->fd);
        if (ret < 0) {
                switch (errno) {
                case EEXIST:
-                       ret = LTTCOMM_KERN_EVENT_EXIST;
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
                        break;
                default:
                        PERROR("enable kernel event");
@@ -319,11 +358,13 @@ int kernel_disable_event(struct ltt_kernel_event *event)
 {
        int ret;
 
+       assert(event);
+
        ret = kernctl_disable(event->fd);
        if (ret < 0) {
                switch (errno) {
                case EEXIST:
-                       ret = LTTCOMM_KERN_EVENT_EXIST;
+                       ret = LTTNG_ERR_KERN_EVENT_EXIST;
                        break;
                default:
                        PERROR("disable kernel event");
@@ -341,17 +382,135 @@ error:
        return ret;
 }
 
+
+int kernel_track_pid(struct ltt_kernel_session *session, int pid)
+{
+       int ret;
+
+       DBG("Kernel track PID %d for session id %" PRIu64 ".",
+                       pid, session->id);
+       ret = kernctl_track_pid(session->fd, pid);
+       if (!ret) {
+               return LTTNG_OK;
+       }
+       switch (errno) {
+       case EINVAL:
+               return LTTNG_ERR_INVALID;
+       case ENOMEM:
+               return LTTNG_ERR_NOMEM;
+       case EEXIST:
+               return LTTNG_ERR_PID_TRACKED;
+       default:
+               return LTTNG_ERR_UNK;
+       }
+}
+
+int kernel_untrack_pid(struct ltt_kernel_session *session, int pid)
+{
+       int ret;
+
+       DBG("Kernel untrack PID %d for session id %" PRIu64 ".",
+                       pid, session->id);
+       ret = kernctl_untrack_pid(session->fd, pid);
+       if (!ret) {
+               return LTTNG_OK;
+       }
+       switch (errno) {
+       case EINVAL:
+               return LTTNG_ERR_INVALID;
+       case ENOMEM:
+               return LTTNG_ERR_NOMEM;
+       case ENOENT:
+               return LTTNG_ERR_PID_NOT_TRACKED;
+       default:
+               return LTTNG_ERR_UNK;
+       }
+}
+
+ssize_t kernel_list_tracker_pids(struct ltt_kernel_session *session,
+               int **_pids)
+{
+       int fd, ret;
+       int pid;
+       ssize_t nbmem, count = 0;
+       FILE *fp;
+       int *pids;
+
+       fd = kernctl_list_tracker_pids(session->fd);
+       if (fd < 0) {
+               PERROR("kernel tracker pids list");
+               goto error;
+       }
+
+       fp = fdopen(fd, "r");
+       if (fp == NULL) {
+               PERROR("kernel tracker pids list fdopen");
+               goto error_fp;
+       }
+
+       nbmem = KERNEL_TRACKER_PIDS_INIT_LIST_SIZE;
+       pids = zmalloc(sizeof(*pids) * nbmem);
+       if (pids == NULL) {
+               PERROR("alloc list pids");
+               count = -ENOMEM;
+               goto end;
+       }
+
+       while (fscanf(fp, "process { pid = %u; };\n", &pid) == 1) {
+               if (count >= nbmem) {
+                       int *new_pids;
+                       size_t new_nbmem;
+
+                       new_nbmem = nbmem << 1;
+                       DBG("Reallocating pids list from %zu to %zu entries",
+                                       nbmem, new_nbmem);
+                       new_pids = realloc(pids, new_nbmem * sizeof(*new_pids));
+                       if (new_pids == NULL) {
+                               PERROR("realloc list events");
+                               free(pids);
+                               count = -ENOMEM;
+                               goto end;
+                       }
+                       /* Zero the new memory */
+                       memset(new_pids + nbmem, 0,
+                               (new_nbmem - nbmem) * sizeof(*new_pids));
+                       nbmem = new_nbmem;
+                       pids = new_pids;
+               }
+               pids[count++] = pid;
+       }
+
+       *_pids = pids;
+       DBG("Kernel list tracker pids done (%zd pids)", count);
+end:
+       ret = fclose(fp);       /* closes both fp and fd */
+       if (ret) {
+               PERROR("fclose");
+       }
+       return count;
+
+error_fp:
+       ret = close(fd);
+       if (ret) {
+               PERROR("close");
+       }
+error:
+       return -1;
+}
+
 /*
  * Create kernel metadata, open from the kernel tracer and add it to the
  * kernel session.
  */
-int kernel_open_metadata(struct ltt_kernel_session *session, char *path)
+int kernel_open_metadata(struct ltt_kernel_session *session)
 {
        int ret;
-       struct ltt_kernel_metadata *lkm;
+       struct ltt_kernel_metadata *lkm = NULL;
+
+       assert(session);
 
        /* Allocate kernel metadata */
-       lkm = trace_kernel_create_metadata(path);
+       lkm = trace_kernel_create_metadata();
        if (lkm == NULL) {
                goto error;
        }
@@ -359,7 +518,7 @@ int kernel_open_metadata(struct ltt_kernel_session *session, char *path)
        /* Kernel tracer metadata creation */
        ret = kernctl_open_metadata(session->fd, &lkm->conf->attr);
        if (ret < 0) {
-               goto error;
+               goto error_open;
        }
 
        lkm->fd = ret;
@@ -371,10 +530,12 @@ int kernel_open_metadata(struct ltt_kernel_session *session, char *path)
 
        session->metadata = lkm;
 
-       DBG("Kernel metadata opened (fd: %d and path: %s)", lkm->fd, lkm->pathname);
+       DBG("Kernel metadata opened (fd: %d)", lkm->fd);
 
        return 0;
 
+error_open:
+       trace_kernel_destroy_metadata(lkm);
 error:
        return -1;
 }
@@ -386,6 +547,8 @@ int kernel_start_session(struct ltt_kernel_session *session)
 {
        int ret;
 
+       assert(session);
+
        ret = kernctl_start_session(session->fd);
        if (ret < 0) {
                PERROR("ioctl start session");
@@ -423,6 +586,8 @@ int kernel_calibrate(int fd, struct lttng_kernel_calibrate *calibrate)
 {
        int ret;
 
+       assert(calibrate);
+
        ret = kernctl_calibrate(fd, calibrate);
        if (ret < 0) {
                PERROR("calibrate ioctl");
@@ -440,9 +605,11 @@ int kernel_metadata_flush_buffer(int fd)
 {
        int ret;
 
+       DBG("Kernel flushing metadata buffer on fd %d", fd);
+
        ret = kernctl_buffer_flush(fd);
        if (ret < 0) {
-               ERR("Fail to flush metadata buffers %d (ret: %d", fd, ret);
+               ERR("Fail to flush metadata buffers %d (ret: %d)", fd, ret);
        }
 
        return 0;
@@ -456,6 +623,8 @@ int kernel_flush_buffer(struct ltt_kernel_channel *channel)
        int ret;
        struct ltt_kernel_stream *stream;
 
+       assert(channel);
+
        DBG("Flush buffer for channel %s", channel->channel->name);
 
        cds_list_for_each_entry(stream, &channel->stream_list.head, list) {
@@ -478,6 +647,8 @@ int kernel_stop_session(struct ltt_kernel_session *session)
 {
        int ret;
 
+       assert(session);
+
        ret = kernctl_stop_session(session->fd);
        if (ret < 0) {
                goto error;
@@ -499,11 +670,13 @@ error:
  */
 int kernel_open_channel_stream(struct ltt_kernel_channel *channel)
 {
-       int ret;
+       int ret, count = 0;
        struct ltt_kernel_stream *lks;
 
+       assert(channel);
+
        while ((ret = kernctl_create_stream(channel->fd)) >= 0) {
-               lks = trace_kernel_create_stream();
+               lks = trace_kernel_create_stream(channel->channel->name, count);
                if (lks == NULL) {
                        ret = close(ret);
                        if (ret) {
@@ -519,19 +692,18 @@ int kernel_open_channel_stream(struct ltt_kernel_channel *channel)
                        PERROR("fcntl session fd");
                }
 
-               ret = asprintf(&lks->pathname, "%s/%s_%d",
-                               channel->pathname, channel->channel->name, channel->stream_count);
-               if (ret < 0) {
-                       PERROR("asprintf kernel create stream");
-                       goto error;
-               }
+               lks->tracefile_size = channel->channel->attr.tracefile_size;
+               lks->tracefile_count = channel->channel->attr.tracefile_count;
 
                /* Add stream to channe stream list */
                cds_list_add(&lks->list, &channel->stream_list.head);
                channel->stream_count++;
 
-               DBG("Kernel stream %d created (fd: %d, state: %d, path: %s)",
-                               channel->stream_count, lks->fd, lks->state, lks->pathname);
+               /* Increment counter which represent CPU number. */
+               count++;
+
+               DBG("Kernel stream %s created (fd: %d, state: %d)", lks->name, lks->fd,
+                               lks->state);
        }
 
        return channel->stream_count;
@@ -547,6 +719,8 @@ int kernel_open_metadata_stream(struct ltt_kernel_session *session)
 {
        int ret;
 
+       assert(session);
+
        ret = kernctl_create_stream(session->metadata->fd);
        if (ret < 0) {
                PERROR("kernel create metadata stream");
@@ -572,13 +746,14 @@ error:
  */
 ssize_t kernel_list_events(int tracer_fd, struct lttng_event **events)
 {
-       int fd, pos, ret;
+       int fd, ret;
        char *event;
        size_t nbmem, count = 0;
-       ssize_t size;
        FILE *fp;
        struct lttng_event *elist;
 
+       assert(events);
+
        fd = kernctl_tracepoint_list(tracer_fd);
        if (fd < 0) {
                PERROR("kernel tracepoint list");
@@ -597,24 +772,39 @@ ssize_t kernel_list_events(int tracer_fd, struct lttng_event **events)
         */
        nbmem = KERNEL_EVENT_INIT_LIST_SIZE;
        elist = zmalloc(sizeof(struct lttng_event) * nbmem);
+       if (elist == NULL) {
+               PERROR("alloc list events");
+               count = -ENOMEM;
+               goto end;
+       }
 
-       while ((size = fscanf(fp, "event { name = %m[^;]; };%n\n", &event, &pos)) == 1) {
+       while (fscanf(fp, "event { name = %m[^;]; };\n", &event) == 1) {
                if (count >= nbmem) {
-                       DBG("Reallocating event list from %zu to %zu bytes", nbmem,
-                                       nbmem * 2);
-                       /* Double the size */
-                       nbmem <<= 1;
-                       elist = realloc(elist, nbmem * sizeof(struct lttng_event));
-                       if (elist == NULL) {
+                       struct lttng_event *new_elist;
+                       size_t new_nbmem;
+
+                       new_nbmem = nbmem << 1;
+                       DBG("Reallocating event list from %zu to %zu bytes",
+                                       nbmem, new_nbmem);
+                       new_elist = realloc(elist, new_nbmem * sizeof(struct lttng_event));
+                       if (new_elist == NULL) {
                                PERROR("realloc list events");
+                               free(event);
+                               free(elist);
                                count = -ENOMEM;
                                goto end;
                        }
+                       /* Zero the new memory */
+                       memset(new_elist + nbmem, 0,
+                               (new_nbmem - nbmem) * sizeof(struct lttng_event));
+                       nbmem = new_nbmem;
+                       elist = new_elist;
                }
                strncpy(elist[count].name, event, LTTNG_SYMBOL_NAME_LEN);
                elist[count].name[LTTNG_SYMBOL_NAME_LEN - 1] = '\0';
                elist[count].enabled = -1;
                count++;
+               free(event);
        }
 
        *events = elist;
@@ -642,28 +832,41 @@ int kernel_validate_version(int tracer_fd)
 {
        int ret;
        struct lttng_kernel_tracer_version version;
+       struct lttng_kernel_tracer_abi_version abi_version;
 
        ret = kernctl_tracer_version(tracer_fd, &version);
        if (ret < 0) {
-               ERR("Failed at getting the lttng-modules version");
+               ERR("Failed to retrieve the lttng-modules version");
                goto error;
        }
 
        /* Validate version */
-       if (version.major != KERN_MODULES_PRE_MAJOR
-               && version.major != KERN_MODULES_MAJOR) {
+       if (version.major != VERSION_MAJOR) {
+               ERR("Kernel tracer major version (%d) is not compatible with lttng-tools major version (%d)",
+                       version.major, VERSION_MAJOR);
                goto error_version;
        }
-
-       DBG2("Kernel tracer version validated (major version %d)", version.major);
+       ret = kernctl_tracer_abi_version(tracer_fd, &abi_version);
+       if (ret < 0) {
+               ERR("Failed to retrieve lttng-modules ABI version");
+               goto error;
+       }
+       if (abi_version.major != LTTNG_MODULES_ABI_MAJOR_VERSION) {
+               ERR("Kernel tracer ABI version (%d.%d) does not match the expected ABI major version (%d.*)",
+                       abi_version.major, abi_version.minor,
+                       LTTNG_MODULES_ABI_MAJOR_VERSION);
+               goto error;
+       }
+       DBG2("Kernel tracer version validated (%d.%d, ABI %d.%d)",
+                       version.major, version.minor,
+                       abi_version.major, abi_version.minor);
        return 0;
 
 error_version:
-       ERR("Kernel major version %d is not compatible (supporting <= %d)",
-                       version.major, KERN_MODULES_MAJOR)
        ret = -1;
 
 error:
+       ERR("Kernel tracer version check failed; kernel tracing will not be available");
        return ret;
 }
 
@@ -699,3 +902,209 @@ int init_kernel_workarounds(void)
 end_boot_id:
        return 0;
 }
+
+/*
+ * Complete teardown of a kernel session.
+ */
+void kernel_destroy_session(struct ltt_kernel_session *ksess)
+{
+       if (ksess == NULL) {
+               DBG3("No kernel session when tearing down session");
+               return;
+       }
+
+       DBG("Tearing down kernel session");
+
+       /*
+        * Destroy channels on the consumer if at least one FD has been sent and we
+        * are in no output mode because the streams are in *no* monitor mode so we
+        * have to send a command to clean them up or else they leaked.
+        */
+       if (!ksess->output_traces && ksess->consumer_fds_sent) {
+               int ret;
+               struct consumer_socket *socket;
+               struct lttng_ht_iter iter;
+
+               /* For each consumer socket. */
+               rcu_read_lock();
+               cds_lfht_for_each_entry(ksess->consumer->socks->ht, &iter.iter,
+                               socket, node.node) {
+                       struct ltt_kernel_channel *chan;
+
+                       /* For each channel, ask the consumer to destroy it. */
+                       cds_list_for_each_entry(chan, &ksess->channel_list.head, list) {
+                               ret = kernel_consumer_destroy_channel(socket, chan);
+                               if (ret < 0) {
+                                       /* Consumer is probably dead. Use next socket. */
+                                       continue;
+                               }
+                       }
+               }
+               rcu_read_unlock();
+       }
+
+       /* Close any relayd session */
+       consumer_output_send_destroy_relayd(ksess->consumer);
+
+       trace_kernel_destroy_session(ksess);
+}
+
+/*
+ * Destroy a kernel channel object. It does not do anything on the tracer side.
+ */
+void kernel_destroy_channel(struct ltt_kernel_channel *kchan)
+{
+       struct ltt_kernel_session *ksess = NULL;
+
+       assert(kchan);
+       assert(kchan->channel);
+
+       DBG3("Kernel destroy channel %s", kchan->channel->name);
+
+       /* Update channel count of associated session. */
+       if (kchan->session) {
+               /* Keep pointer reference so we can update it after the destroy. */
+               ksess = kchan->session;
+       }
+
+       trace_kernel_destroy_channel(kchan);
+
+       /*
+        * At this point the kernel channel is not visible anymore. This is safe
+        * since in order to work on a visible kernel session, the tracing session
+        * lock (ltt_session.lock) MUST be acquired.
+        */
+       if (ksess) {
+               ksess->channel_count--;
+       }
+}
+
+/*
+ * Take a snapshot for a given kernel session.
+ *
+ * Return 0 on success or else return a LTTNG_ERR code.
+ */
+int kernel_snapshot_record(struct ltt_kernel_session *ksess,
+               struct snapshot_output *output, int wait,
+               uint64_t nb_packets_per_stream)
+{
+       int err, ret, saved_metadata_fd;
+       struct consumer_socket *socket;
+       struct lttng_ht_iter iter;
+       struct ltt_kernel_metadata *saved_metadata;
+
+       assert(ksess);
+       assert(ksess->consumer);
+       assert(output);
+
+       DBG("Kernel snapshot record started");
+
+       /* Save current metadata since the following calls will change it. */
+       saved_metadata = ksess->metadata;
+       saved_metadata_fd = ksess->metadata_stream_fd;
+
+       rcu_read_lock();
+
+       ret = kernel_open_metadata(ksess);
+       if (ret < 0) {
+               ret = LTTNG_ERR_KERN_META_FAIL;
+               goto error;
+       }
+
+       ret = kernel_open_metadata_stream(ksess);
+       if (ret < 0) {
+               ret = LTTNG_ERR_KERN_META_FAIL;
+               goto error_open_stream;
+       }
+
+       /* Send metadata to consumer and snapshot everything. */
+       cds_lfht_for_each_entry(ksess->consumer->socks->ht, &iter.iter,
+                       socket, node.node) {
+               struct consumer_output *saved_output;
+               struct ltt_kernel_channel *chan;
+
+               /*
+                * Temporarly switch consumer output for our snapshot output. As long
+                * as the session lock is taken, this is safe.
+                */
+               saved_output = ksess->consumer;
+               ksess->consumer = output->consumer;
+
+               pthread_mutex_lock(socket->lock);
+               /* This stream must not be monitored by the consumer. */
+               ret = kernel_consumer_add_metadata(socket, ksess, 0);
+               pthread_mutex_unlock(socket->lock);
+               /* Put back the saved consumer output into the session. */
+               ksess->consumer = saved_output;
+               if (ret < 0) {
+                       ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                       goto error_consumer;
+               }
+
+               /* For each channel, ask the consumer to snapshot it. */
+               cds_list_for_each_entry(chan, &ksess->channel_list.head, list) {
+                       pthread_mutex_lock(socket->lock);
+                       ret = consumer_snapshot_channel(socket, chan->fd, output, 0,
+                                       ksess->uid, ksess->gid,
+                                       DEFAULT_KERNEL_TRACE_DIR, wait,
+                                       nb_packets_per_stream);
+                       pthread_mutex_unlock(socket->lock);
+                       if (ret < 0) {
+                               ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                               (void) kernel_consumer_destroy_metadata(socket,
+                                               ksess->metadata);
+                               goto error_consumer;
+                       }
+               }
+
+               /* Snapshot metadata, */
+               pthread_mutex_lock(socket->lock);
+               ret = consumer_snapshot_channel(socket, ksess->metadata->fd, output,
+                               1, ksess->uid, ksess->gid,
+                               DEFAULT_KERNEL_TRACE_DIR, wait, 0);
+               pthread_mutex_unlock(socket->lock);
+               if (ret < 0) {
+                       ret = LTTNG_ERR_KERN_CONSUMER_FAIL;
+                       goto error_consumer;
+               }
+
+               /*
+                * The metadata snapshot is done, ask the consumer to destroy it since
+                * it's not monitored on the consumer side.
+                */
+               (void) kernel_consumer_destroy_metadata(socket, ksess->metadata);
+       }
+
+       ret = LTTNG_OK;
+
+error_consumer:
+       /* Close newly opened metadata stream. It's now on the consumer side. */
+       err = close(ksess->metadata_stream_fd);
+       if (err < 0) {
+               PERROR("close snapshot kernel");
+       }
+
+error_open_stream:
+       trace_kernel_destroy_metadata(ksess->metadata);
+error:
+       /* Restore metadata state.*/
+       ksess->metadata = saved_metadata;
+       ksess->metadata_stream_fd = saved_metadata_fd;
+
+       rcu_read_unlock();
+       return ret;
+}
+
+/*
+ * Get the syscall mask array from the kernel tracer.
+ *
+ * Return 0 on success else a negative value. In both case, syscall_mask should
+ * be freed.
+ */
+int kernel_syscall_mask(int chan_fd, char **syscall_mask, uint32_t *nr_bits)
+{
+       assert(syscall_mask);
+       assert(nr_bits);
+
+       return kernctl_syscall_mask(chan_fd, syscall_mask, nr_bits);
+}
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