Add support for UST application registration
[lttng-tools.git] / ltt-sessiond / main.c
index 567742ebb783bc1a4bfdf9f6ff89ddc8193f1604..b636986f832d7352b572c5a08fbcbaf92ceadfc7 100644 (file)
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
-#include <sys/ipc.h>
 #include <sys/mount.h>
-#include <sys/shm.h>
+#include <sys/resource.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
-#include <sys/time.h>
-#include <sys/resource.h>
 #include <unistd.h>
 
-#include <urcu/list.h>         /* URCU list library (-lurcu) */
-#include <lttng/lttng.h>
+#include <ltt-kconsumerd.h>
+#include <lttng-sessiond-comm.h>
+#include <lttng/lttng-kconsumerd.h>
+#include <lttngerr.h>
 
 #include "context.h"
-#include "liblttsessiondcomm.h"
-#include "ltt-sessiond.h"
-#include "lttngerr.h"
+#include "futex.h"
 #include "kernel-ctl.h"
-#include "ust-ctl.h"
-#include "session.h"
+#include "ltt-sessiond.h"
 #include "traceable-app.h"
-#include "lttng-kconsumerd.h"
+#include "ust-ctl.h"
 #include "utils.h"
+#include "ust-comm.h"
 
 /* Const values */
 const char default_home_dir[] = DEFAULT_HOME_DIR;
@@ -72,6 +69,7 @@ static int is_root;                   /* Set to 1 if the daemon is running as root */
 static pid_t ppid;          /* Parent PID for --sig-parent option */
 static pid_t kconsumerd_pid;
 static struct pollfd *kernel_pollfd;
+static int dispatch_thread_exit;
 
 static char apps_unix_sock_path[PATH_MAX];                             /* Global application Unix socket path */
 static char client_unix_sock_path[PATH_MAX];                   /* Global client Unix socket path */
@@ -92,17 +90,34 @@ static int kernel_poll_pipe[2];
  */
 static int thread_quit_pipe[2];
 
+/*
+ * This pipe is used to inform the thread managing application communication
+ * that a command is queued and ready to be processed.
+ */
+static int apps_cmd_pipe[2];
+
 /* Pthread, Mutexes and Semaphores */
 static pthread_t kconsumerd_thread;
 static pthread_t apps_thread;
+static pthread_t reg_apps_thread;
 static pthread_t client_thread;
 static pthread_t kernel_thread;
+static pthread_t dispatch_thread;
 static sem_t kconsumerd_sem;
 
 static pthread_mutex_t kconsumerd_pid_mutex;   /* Mutex to control kconsumerd pid assignation */
 
 static int modprobe_remove_kernel_modules(void);
 
+/*
+ * UST registration command queue. This queue is tied with a futex and uses a N
+ * wakers / 1 waiter implemented and detailed in futex.c/.h
+ *
+ * The thread_manage_apps and thread_dispatch_ust_registration interact with
+ * this queue and the wait/wake scheme.
+ */
+static struct ust_cmd_queue ust_cmd_queue;
+
 /*
  * Pointer initialized before thread creation.
  *
@@ -158,18 +173,33 @@ static void teardown_kernel_session(struct ltt_session *session)
 {
        if (session->kernel_session != NULL) {
                DBG("Tearing down kernel session");
+
+               /*
+                * If a custom kernel consumer was registered, close the socket before
+                * tearing down the complete kernel session structure
+                */
+               if (session->kernel_session->consumer_fd != kconsumerd_cmd_sock) {
+                       lttcomm_close_unix_sock(session->kernel_session->consumer_fd);
+               }
+
                trace_destroy_kernel_session(session->kernel_session);
                /* Extra precaution */
                session->kernel_session = NULL;
        }
 }
 
+/*
+ * Stop all threads by closing the thread quit pipe.
+ */
 static void stop_threads(void)
 {
        /* Stopping all threads */
        DBG("Terminating all threads");
        close(thread_quit_pipe[0]);
        close(thread_quit_pipe[1]);
+       /* Dispatch thread */
+       dispatch_thread_exit = 1;
+       futex_nto1_wake(&ust_cmd_queue.futex);
 }
 
 /*
@@ -214,6 +244,9 @@ static void cleanup(void)
                }
        }
 
+       DBG("Closing all UST sockets");
+       clean_traceable_apps_list();
+
        pthread_mutex_destroy(&kconsumerd_pid_mutex);
 
        DBG("Closing kernel fd");
@@ -288,7 +321,9 @@ static int send_kconsumerd_channel_fds(int sock, struct ltt_kernel_channel *chan
                        lkm.fd = stream->fd;
                        lkm.state = stream->state;
                        lkm.max_sb_size = channel->channel->attr.subbuf_size;
+                       lkm.output = channel->channel->attr.output;
                        strncpy(lkm.path_name, stream->pathname, PATH_MAX);
+                       lkm.path_name[PATH_MAX - 1] = '\0';
 
                        DBG("Sending fd %d to kconsumerd", lkm.fd);
 
@@ -311,7 +346,7 @@ error:
 /*
  * Send all stream fds of the kernel session to the consumer.
  */
-static int send_kconsumerd_fds(int sock, struct ltt_kernel_session *session)
+static int send_kconsumerd_fds(struct ltt_kernel_session *session)
 {
        int ret;
        struct ltt_kernel_channel *chan;
@@ -324,7 +359,7 @@ static int send_kconsumerd_fds(int sock, struct ltt_kernel_session *session)
 
        DBG("Sending kconsumerd header for metadata");
 
-       ret = lttcomm_send_unix_sock(sock, &lkh, sizeof(struct lttcomm_kconsumerd_header));
+       ret = lttcomm_send_unix_sock(session->consumer_fd, &lkh, sizeof(struct lttcomm_kconsumerd_header));
        if (ret < 0) {
                perror("send kconsumerd header");
                goto error;
@@ -332,14 +367,21 @@ static int send_kconsumerd_fds(int sock, struct ltt_kernel_session *session)
 
        DBG("Sending metadata stream fd");
 
+       /* Extra protection. It's NOT suppose to be set to 0 at this point */
+       if (session->consumer_fd == 0) {
+               session->consumer_fd = kconsumerd_cmd_sock;
+       }
+
        if (session->metadata_stream_fd != 0) {
                /* Send metadata stream fd first */
                lkm.fd = session->metadata_stream_fd;
                lkm.state = ACTIVE_FD;
                lkm.max_sb_size = session->metadata->conf->attr.subbuf_size;
+               lkm.output = DEFAULT_KERNEL_CHANNEL_OUTPUT;
                strncpy(lkm.path_name, session->metadata->pathname, PATH_MAX);
+               lkm.path_name[PATH_MAX - 1] = '\0';
 
-               ret = lttcomm_send_fds_unix_sock(sock, &lkm, &lkm.fd, 1, sizeof(lkm));
+               ret = lttcomm_send_fds_unix_sock(session->consumer_fd, &lkm, &lkm.fd, 1, sizeof(lkm));
                if (ret < 0) {
                        perror("send kconsumerd fd");
                        goto error;
@@ -347,7 +389,7 @@ static int send_kconsumerd_fds(int sock, struct ltt_kernel_session *session)
        }
 
        cds_list_for_each_entry(chan, &session->channel_list.head, list) {
-               ret = send_kconsumerd_channel_fds(sock, chan);
+               ret = send_kconsumerd_channel_fds(session->consumer_fd, chan);
                if (ret < 0) {
                        goto error;
                }
@@ -389,7 +431,6 @@ static int ust_connect_app(pid_t pid)
 
        return sock;
 }
-#endif /* DISABLED */
 
 /*
  * Notify apps by writing 42 to a named pipe using name. Every applications
@@ -420,6 +461,7 @@ static int notify_apps(const char *name)
 error:
        return ret;
 }
+#endif /* DISABLED */
 
 /*
  * Setup the outgoing data buffer for the response (llm) by allocating the
@@ -546,6 +588,12 @@ static int update_kernel_stream(int fd)
                        unlock_session(session);
                        continue;
                }
+
+               /* This is not suppose to be 0 but this is an extra security check */
+               if (session->kernel_session->consumer_fd == 0) {
+                       session->kernel_session->consumer_fd = kconsumerd_cmd_sock;
+               }
+
                cds_list_for_each_entry(channel, &session->kernel_session->channel_list.head, list) {
                        if (channel->fd == fd) {
                                DBG("Channel found, updating kernel streams");
@@ -553,12 +601,14 @@ static int update_kernel_stream(int fd)
                                if (ret < 0) {
                                        goto end;
                                }
+
                                /*
                                 * Have we already sent fds to the consumer? If yes, it means that
                                 * tracing is started so it is safe to send our updated stream fds.
                                 */
                                if (session->kernel_session->kconsumer_fds_sent == 1) {
-                                       ret = send_kconsumerd_channel_fds(kconsumerd_cmd_sock, channel);
+                                       ret = send_kconsumerd_channel_fds(session->kernel_session->consumer_fd,
+                                                       channel);
                                        if (ret < 0) {
                                                goto end;
                                        }
@@ -726,6 +776,25 @@ static void *thread_manage_kconsumerd(void *data)
                goto error;
        }
 
+       /* Kconsumerd err socket */
+       pollfd[1].fd = sock;
+       pollfd[1].events = POLLIN;
+
+       /* Inifinite blocking call, waiting for transmission */
+       ret = poll(pollfd, 2, -1);
+       if (ret < 0) {
+               perror("poll kconsumerd thread");
+               goto error;
+       }
+
+       /* Thread quit pipe has been closed. Killing thread. */
+       if (pollfd[0].revents == POLLNVAL) {
+               goto error;
+       } else if (pollfd[1].revents == POLLERR) {
+               ERR("Kconsumerd err socket second poll error");
+               goto error;
+       }
+
        /* Wait for any kconsumerd error */
        ret = lttcomm_recv_unix_sock(sock, &code, sizeof(enum lttcomm_return_code));
        if (ret <= 0) {
@@ -755,24 +824,232 @@ error:
 }
 
 /*
- *     This thread manage the application socket communication
+ * Reallocate the apps command pollfd structure of nb_fd size.
+ *
+ * The first two fds must be there at all time.
+ */
+static int update_apps_cmd_pollfd(unsigned int nb_fd, struct pollfd **pollfd)
+{
+       /* Can't accept pollfd less than 2 */
+       if (nb_fd < 2) {
+               goto end;
+       }
+
+       *pollfd = realloc(*pollfd, nb_fd * sizeof(struct pollfd));
+       if (*pollfd == NULL) {
+               perror("realloc manage apps pollfd");
+               goto error;
+       }
+
+       /* First fd is always the quit pipe */
+       (*pollfd)[0].fd = thread_quit_pipe[0];
+       /* Apps command pipe */
+       (*pollfd)[1].fd = apps_cmd_pipe[0];
+       (*pollfd)[1].events = POLLIN;
+
+       DBG("Apps cmd pollfd realloc of size %d", nb_fd);
+
+end:
+       return 0;
+
+error:
+       return -1;
+}
+
+/*
+ * Send registration done packet to the application.
+ */
+static int send_ust_register_done(int sock)
+{
+       struct lttcomm_ust_msg lum;
+
+       DBG("Sending register done command to %d", sock);
+
+       lum.cmd = LTTNG_UST_REGISTER_DONE;
+       lum.handle = LTTNG_UST_ROOT_HANDLE;
+
+       return ustcomm_send_command(sock, &lum);
+}
+
+/*
+ * This thread manage application communication.
  */
 static void *thread_manage_apps(void *data)
+{
+       int i, ret, count;
+       unsigned int nb_fd = 2;
+       int update_poll_flag = 1;
+       struct pollfd *pollfd = NULL;
+       struct ust_command ust_cmd;
+
+       DBG("[thread] Manage application started");
+
+       ust_cmd.sock = -1;
+
+       while (1) {
+               /* See if we have a valid socket to add to pollfd */
+               if (ust_cmd.sock != -1) {
+                       nb_fd++;
+                       update_poll_flag = 1;
+               }
+
+               /* The pollfd struct must be updated */
+               if (update_poll_flag) {
+                       ret = update_apps_cmd_pollfd(nb_fd, &pollfd);
+                       if (ret < 0) {
+                               /* malloc failed so we quit */
+                               goto error;
+                       }
+                       if (ust_cmd.sock != -1) {
+                               /* Update pollfd with the new UST socket */
+                               DBG("Adding sock %d to apps cmd pollfd", ust_cmd.sock);
+                               pollfd[nb_fd - 1].fd = ust_cmd.sock;
+                               pollfd[nb_fd - 1].events = POLLHUP | POLLNVAL;
+                               ust_cmd.sock = -1;
+                       }
+               }
+
+               DBG("Apps thread polling on %d fds", nb_fd);
+
+               /* Inifinite blocking call, waiting for transmission */
+               ret = poll(pollfd, nb_fd, -1);
+               if (ret < 0) {
+                       perror("poll apps thread");
+                       goto error;
+               }
+
+               /* Thread quit pipe has been closed. Killing thread. */
+               if (pollfd[0].revents == POLLNVAL) {
+                       goto error;
+               } else if (pollfd[1].revents == POLLERR) {
+                       ERR("Apps command pipe poll error");
+                       goto error;
+               } else if (pollfd[1].revents == POLLIN) {
+                       /* Empty pipe */
+                       ret = read(apps_cmd_pipe[0], &ust_cmd, sizeof(ust_cmd));
+                       if (ret < 0 || ret < sizeof(ust_cmd)) {
+                               perror("read apps cmd pipe");
+                               goto error;
+                       }
+
+                       /* Register applicaton to the session daemon */
+                       ret = register_traceable_app(&ust_cmd.reg_msg, ust_cmd.sock);
+                       if (ret < 0) {
+                               /* Only critical ENOMEM error can be returned here */
+                               goto error;
+                       }
+
+                       ret = send_ust_register_done(ust_cmd.sock);
+                       if (ret < 0) {
+                               /*
+                                * If the registration is not possible, we simply unregister
+                                * the apps and continue
+                                */
+                               unregister_traceable_app(ust_cmd.sock);
+                       }
+               }
+
+               count = nb_fd;
+               for (i = 2; i < count; i++) {
+                       /* Apps socket is closed/hungup */
+                       switch (pollfd[i].revents) {
+                       case POLLNVAL:
+                       case POLLHUP:
+                               /* Pipe closed */
+                               unregister_traceable_app(pollfd[i].fd);
+                               nb_fd--;
+                       }
+               }
+
+               if (nb_fd != count) {
+                       update_poll_flag = 1;
+               }
+       }
+
+error:
+       DBG("Application communication apps dying");
+       close(apps_cmd_pipe[0]);
+       close(apps_cmd_pipe[1]);
+
+       free(pollfd);
+
+       return NULL;
+}
+
+/*
+ * Dispatch request from the registration threads to the application
+ * communication thread.
+ */
+static void *thread_dispatch_ust_registration(void *data)
+{
+       int ret;
+       struct cds_wfq_node *node;
+       struct ust_command *ust_cmd = NULL;
+
+       DBG("[thread] Dispatch UST command started");
+
+       while (!dispatch_thread_exit) {
+               /* Atomically prepare the queue futex */
+               futex_nto1_prepare(&ust_cmd_queue.futex);
+
+               do {
+                       /* Dequeue command for registration */
+                       node = cds_wfq_dequeue_blocking(&ust_cmd_queue.queue);
+                       if (node == NULL) {
+                               DBG("Waked up but nothing in the UST command queue");
+                               /* Continue thread execution */
+                               break;
+                       }
+
+                       ust_cmd = caa_container_of(node, struct ust_command, node);
+
+                       DBG("Dispatching UST registration pid:%d sock:%d",
+                                       ust_cmd->reg_msg.pid, ust_cmd->sock);
+                       /*
+                        * Inform apps thread of the new application registration. This
+                        * call is blocking so we can be assured that the data will be read
+                        * at some point in time or wait to the end of the world :)
+                        */
+                       ret = write(apps_cmd_pipe[1], ust_cmd,
+                                       sizeof(struct ust_command));
+                       if (ret < 0) {
+                               perror("write apps cmd pipe");
+                               if (errno == EBADF) {
+                                       /*
+                                        * We can't inform the application thread to process
+                                        * registration. We will exit or else application
+                                        * registration will not occur and tracing will never
+                                        * start.
+                                        */
+                                       goto error;
+                               }
+                       }
+                       free(ust_cmd);
+               } while (node != NULL);
+
+               /* Futex wait on queue. Blocking call on futex() */
+               futex_nto1_wait(&ust_cmd_queue.futex);
+       }
+
+error:
+       DBG("Dispatch thread dying");
+       return NULL;
+}
+
+/*
+ * This thread manage application registration.
+ */
+static void *thread_registration_apps(void *data)
 {
        int sock = 0, ret;
        struct pollfd pollfd[2];
+       /*
+        * Get allocated in this thread, enqueued to a global queue, dequeued and
+        * freed in the manage apps thread.
+        */
+       struct ust_command *ust_cmd = NULL;
 
-       /* TODO: Something more elegant is needed but fine for now */
-       /* FIXME: change all types to either uint8_t, uint32_t, uint64_t
-        * for 32-bit vs 64-bit compat processes. */
-       /* replicate in ust with version number */
-       struct {
-               int reg;        /* 1:register, 0:unregister */
-               pid_t pid;
-               uid_t uid;
-       } reg_msg;
-
-       DBG("[thread] Manage apps started");
+       DBG("[thread] Manage application registration started");
 
        ret = lttcomm_listen_unix_sock(apps_sock);
        if (ret < 0) {
@@ -787,7 +1064,7 @@ static void *thread_manage_apps(void *data)
        pollfd[1].events = POLLIN;
 
        /* Notify all applications to register */
-       notify_apps(default_global_apps_pipe);
+       //notify_apps(default_global_apps_pipe);
 
        while (1) {
                DBG("Accepting application registration");
@@ -795,7 +1072,7 @@ static void *thread_manage_apps(void *data)
                /* Inifinite blocking call, waiting for transmission */
                ret = poll(pollfd, 2, -1);
                if (ret < 0) {
-                       perror("poll apps thread");
+                       perror("poll register apps thread");
                        goto error;
                }
 
@@ -803,7 +1080,7 @@ static void *thread_manage_apps(void *data)
                if (pollfd[0].revents == POLLNVAL) {
                        goto error;
                } else if (pollfd[1].revents == POLLERR) {
-                       ERR("Apps socket poll error");
+                       ERR("Register apps socket poll error");
                        goto error;
                }
 
@@ -812,34 +1089,46 @@ static void *thread_manage_apps(void *data)
                        goto error;
                }
 
+               /* Create UST registration command for enqueuing */
+               ust_cmd = malloc(sizeof(struct ust_command));
+               if (ust_cmd == NULL) {
+                       perror("ust command malloc");
+                       goto error;
+               }
+
                /*
-                * Basic recv here to handle the very simple data
-                * that the libust send to register (reg_msg).
+                * Using message-based transmissions to ensure we don't have to deal
+                * with partially received messages.
                 */
-               ret = recv(sock, &reg_msg, sizeof(reg_msg), 0);
-               if (ret < 0) {
-                       perror("recv");
+               ret = lttcomm_recv_unix_sock(sock, &ust_cmd->reg_msg,
+                               sizeof(struct ust_register_msg));
+               if (ret < 0 || ret != sizeof(struct ust_register_msg)) {
+                       perror("lttcomm_recv_unix_sock register apps");
+                       free(ust_cmd);
+                       close(sock);
                        continue;
                }
 
-               /* Add application to the global traceable list */
-               if (reg_msg.reg == 1) {
-                       /* Registering */
-                       ret = register_traceable_app(reg_msg.pid, reg_msg.uid);
-                       if (ret < 0) {
-                               /* register_traceable_app only return an error with
-                                * ENOMEM. At this point, we better stop everything.
-                                */
-                               goto error;
-                       }
-               } else {
-                       /* Unregistering */
-                       unregister_traceable_app(reg_msg.pid);
-               }
+               ust_cmd->sock = sock;
+
+               /*
+                * Lock free enqueue the registration request.
+                * The red pill has been taken! This apps will be part of the *system*
+                */
+               cds_wfq_enqueue(&ust_cmd_queue.queue, &ust_cmd->node);
+
+               /*
+                * Wake the registration queue futex.
+                * Implicit memory barrier with the exchange in cds_wfq_enqueue.
+                */
+               futex_nto1_wake(&ust_cmd_queue.futex);
+
+               DBG("Thread manage apps informed of queued node with sock:%d pid:%d",
+                               sock, ust_cmd->reg_msg.pid);
        }
 
 error:
-       DBG("Apps thread dying");
+       DBG("Register apps thread dying");
        if (apps_sock) {
                close(apps_sock);
        }
@@ -883,6 +1172,9 @@ error:
        return ret;
 }
 
+/*
+ * Join kernel consumer thread
+ */
 static int join_kconsumerd_thread(void)
 {
        void *status;
@@ -1005,7 +1297,7 @@ static int modprobe_kernel_modules(void)
                        ERR("Unable to launch modprobe for module %s",
                                kernel_modules_list[i].name);
                } else if (kernel_modules_list[i].required
-                          && WEXITSTATUS(ret) != 0) {
+                               && WEXITSTATUS(ret) != 0) {
                        ERR("Unable to load module %s",
                                kernel_modules_list[i].name);
                } else {
@@ -1041,7 +1333,7 @@ static int modprobe_remove_kernel_modules(void)
                        ERR("Unable to launch modprobe --remove for module %s",
                                kernel_modules_list[i].name);
                } else if (kernel_modules_list[i].required
-                          && WEXITSTATUS(ret) != 0) {
+                               && WEXITSTATUS(ret) != 0) {
                        ERR("Unable to remove module %s",
                                kernel_modules_list[i].name);
                } else {
@@ -1169,7 +1461,16 @@ static int start_kernel_trace(struct ltt_kernel_session *session)
        int ret = 0;
 
        if (session->kconsumer_fds_sent == 0) {
-               ret = send_kconsumerd_fds(kconsumerd_cmd_sock, session);
+               /*
+                * Assign default kernel consumer if no consumer assigned to the kernel
+                * session. At this point, it's NOT suppose to be 0 but this is an extra
+                * security check.
+                */
+               if (session->consumer_fd == 0) {
+                       session->consumer_fd = kconsumerd_cmd_sock;
+               }
+
+               ret = send_kconsumerd_fds(session);
                if (ret < 0) {
                        ERR("Send kconsumerd fds failed");
                        ret = LTTCOMM_KERN_CONSUMER_FAIL;
@@ -1202,7 +1503,8 @@ static int notify_kernel_pollfd(void)
 /*
  * Allocate a channel structure and fill it.
  */
-static struct lttng_channel *init_default_channel(char *name)
+static struct lttng_channel *init_default_channel(enum lttng_domain_type domain_type,
+                                               char *name)
 {
        struct lttng_channel *chan;
 
@@ -1214,18 +1516,29 @@ static struct lttng_channel *init_default_channel(char *name)
 
        if (snprintf(chan->name, NAME_MAX, "%s", name) < 0) {
                perror("snprintf channel name");
-               return NULL;
+               goto error;
        }
 
        chan->attr.overwrite = DEFAULT_CHANNEL_OVERWRITE;
-       chan->attr.subbuf_size = DEFAULT_CHANNEL_SUBBUF_SIZE;
-       chan->attr.num_subbuf = DEFAULT_CHANNEL_SUBBUF_NUM;
        chan->attr.switch_timer_interval = DEFAULT_CHANNEL_SWITCH_TIMER;
        chan->attr.read_timer_interval = DEFAULT_CHANNEL_READ_TIMER;
-       chan->attr.output = DEFAULT_KERNEL_CHANNEL_OUTPUT;
 
-error:
+       switch (domain_type) {
+       case LTTNG_DOMAIN_KERNEL:
+               chan->attr.subbuf_size = DEFAULT_KERNEL_CHANNEL_SUBBUF_SIZE;
+               chan->attr.num_subbuf = DEFAULT_KERNEL_CHANNEL_SUBBUF_NUM;
+               chan->attr.output = DEFAULT_KERNEL_CHANNEL_OUTPUT;
+               break;
+               /* TODO: add UST */
+       default:
+               goto error;     /* Not implemented */
+       }
+
        return chan;
+
+error:
+       free(chan);
+       return NULL;
 }
 
 /*
@@ -1243,8 +1556,20 @@ static int create_kernel_session(struct ltt_session *session)
                goto error;
        }
 
-       ret = mkdir_recursive(session->path, S_IRWXU | S_IRWXG,
-                             geteuid(), allowed_group()); 
+       /* Set kernel consumer socket fd */
+       if (kconsumerd_cmd_sock) {
+               session->kernel_session->consumer_fd = kconsumerd_cmd_sock;
+       }
+
+       ret = asprintf(&session->kernel_session->trace_path, "%s/kernel",
+                       session->path);
+       if (ret < 0) {
+               perror("asprintf kernel traces path");
+               goto error;
+       }
+
+       ret = mkdir_recursive(session->kernel_session->trace_path,
+                       S_IRWXU | S_IRWXG, geteuid(), allowed_group());
        if (ret < 0) {
                if (ret != -EEXIST) {
                        ERR("Trace directory creation error");
@@ -1275,7 +1600,9 @@ static void list_lttng_sessions(struct lttng_session *sessions)
         */
        cds_list_for_each_entry(session, &session_list_ptr->head, list) {
                strncpy(sessions[i].path, session->path, PATH_MAX);
+               sessions[i].path[PATH_MAX - 1] = '\0';
                strncpy(sessions[i].name, session->name, NAME_MAX);
+               sessions[i].name[NAME_MAX - 1] = '\0';
                i++;
        }
 }
@@ -1321,6 +1648,7 @@ static void list_lttng_events(struct ltt_kernel_channel *kchan,
        /* Kernel channels */
        cds_list_for_each_entry(event, &kchan->events_list.head , list) {
                strncpy(events[i].name, event->event->name, LTTNG_SYMBOL_NAME_LEN);
+               events[i].name[LTTNG_SYMBOL_NAME_LEN - 1] = '\0';
                events[i].enabled = event->enabled;
                switch (event->event->instrumentation) {
                        case LTTNG_KERNEL_TRACEPOINT:
@@ -1355,7 +1683,9 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
 
        DBG("Processing client command %d", cmd_ctx->lsm->cmd_type);
 
-       /* Listing commands don't need a session */
+       /*
+        * Commands that DO NOT need a session.
+        */
        switch (cmd_ctx->lsm->cmd_type) {
        case LTTNG_CREATE_SESSION:
        case LTTNG_LIST_SESSIONS:
@@ -1396,10 +1726,10 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
 
                /* Need a session for kernel command */
                switch (cmd_ctx->lsm->cmd_type) {
+               case LTTNG_CALIBRATE:
                case LTTNG_CREATE_SESSION:
                case LTTNG_LIST_SESSIONS:
                case LTTNG_LIST_TRACEPOINTS:
-               case LTTNG_CALIBRATE:
                        break;
                default:
                        if (cmd_ctx->session->kernel_session == NULL) {
@@ -1410,7 +1740,9 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                                }
 
                                /* Start the kernel consumer daemon */
-                               if (kconsumerd_pid == 0) {
+
+                               if (kconsumerd_pid == 0 &&
+                                               cmd_ctx->lsm->cmd_type != LTTNG_REGISTER_CONSUMER) {
                                        ret = start_kconsumerd();
                                        if (ret < 0) {
                                                goto error;
@@ -1444,6 +1776,7 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                        strncpy(kctx.u.perf_counter.name,
                                        cmd_ctx->lsm->u.context.ctx.u.perf_counter.name,
                                        LTTNG_SYMBOL_NAME_LEN);
+                       kctx.u.perf_counter.name[LTTNG_SYMBOL_NAME_LEN - 1] = '\0';
 
                        /* Add kernel context to kernel tracer. See context.c */
                        ret = add_kernel_context(cmd_ctx->session->kernel_session, &kctx,
@@ -1603,7 +1936,8 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                                DBG("Creating kernel channel");
 
                                ret = kernel_create_channel(cmd_ctx->session->kernel_session,
-                                               &cmd_ctx->lsm->u.channel.chan, cmd_ctx->session->path);
+                                               &cmd_ctx->lsm->u.channel.chan,
+                                               cmd_ctx->session->kernel_session->trace_path);
                                if (ret < 0) {
                                        ret = LTTCOMM_KERN_CHAN_FAIL;
                                        goto error;
@@ -1653,26 +1987,32 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
 
                switch (cmd_ctx->lsm->domain.type) {
                case LTTNG_DOMAIN_KERNEL:
-                       do {
+                       kchan = get_kernel_channel_by_name(channel_name,
+                                       cmd_ctx->session->kernel_session);
+                       if (kchan == NULL) {
+                               DBG("Channel not found. Creating channel %s", channel_name);
+
+                               chan = init_default_channel(cmd_ctx->lsm->domain.type, channel_name);
+                               if (chan == NULL) {
+                                       ret = LTTCOMM_FATAL;
+                                       goto error;
+                               }
+
+                               ret = kernel_create_channel(cmd_ctx->session->kernel_session,
+                                               chan, cmd_ctx->session->kernel_session->trace_path);
+                               if (ret < 0) {
+                                       ret = LTTCOMM_KERN_CHAN_FAIL;
+                                       goto error;
+                               }
                                kchan = get_kernel_channel_by_name(channel_name,
                                                cmd_ctx->session->kernel_session);
                                if (kchan == NULL) {
-                                       DBG("Channel not found. Creating channel %s", channel_name);
-
-                                       chan = init_default_channel(channel_name);
-                                       if (chan == NULL) {
-                                               ret = LTTCOMM_FATAL;
-                                               goto error;
-                                       }
-
-                                       ret = kernel_create_channel(cmd_ctx->session->kernel_session,
-                                                       chan, cmd_ctx->session->path);
-                                       if (ret < 0) {
-                                               ret = LTTCOMM_KERN_CHAN_FAIL;
-                                               goto error;
-                                       }
+                                       ERR("Channel %s not found after creation. Internal error, giving up.",
+                                               channel_name);
+                                       ret = LTTCOMM_FATAL;
+                                       goto error;
                                }
-                       } while (kchan == NULL);
+                       }
 
                        kevent = get_kernel_event_by_name(cmd_ctx->lsm->u.enable.event.name, kchan);
                        if (kevent == NULL) {
@@ -1725,26 +2065,32 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
 
                switch (cmd_ctx->lsm->domain.type) {
                case LTTNG_DOMAIN_KERNEL:
-                       do {
+                       kchan = get_kernel_channel_by_name(channel_name,
+                                       cmd_ctx->session->kernel_session);
+                       if (kchan == NULL) {
+                               DBG("Channel not found. Creating channel %s", channel_name);
+
+                               chan = init_default_channel(cmd_ctx->lsm->domain.type, channel_name);
+                               if (chan == NULL) {
+                                       ret = LTTCOMM_FATAL;
+                                       goto error;
+                               }
+
+                               ret = kernel_create_channel(cmd_ctx->session->kernel_session,
+                                               chan, cmd_ctx->session->kernel_session->trace_path);
+                               if (ret < 0) {
+                                       ret = LTTCOMM_KERN_CHAN_FAIL;
+                                       goto error;
+                               }
                                kchan = get_kernel_channel_by_name(channel_name,
                                                cmd_ctx->session->kernel_session);
                                if (kchan == NULL) {
-                                       DBG("Channel not found. Creating channel %s", channel_name);
-
-                                       chan = init_default_channel(channel_name);
-                                       if (chan == NULL) {
-                                               ret = LTTCOMM_FATAL;
-                                               goto error;
-                                       }
-
-                                       ret = kernel_create_channel(cmd_ctx->session->kernel_session,
-                                                       chan, cmd_ctx->session->path);
-                                       if (ret < 0) {
-                                               ret = LTTCOMM_KERN_CHAN_FAIL;
-                                               goto error;
-                                       }
+                                       ERR("Channel %s not found after creation. Internal error, giving up.",
+                                               channel_name);
+                                       ret = LTTCOMM_FATAL;
+                                       goto error;
                                }
-                       } while (kchan == NULL);
+                       }
 
                        /* For each event in the kernel session */
                        cds_list_for_each_entry(kevent, &kchan->events_list.head, list) {
@@ -1843,7 +2189,7 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                        if (cmd_ctx->session->kernel_session->metadata == NULL) {
                                DBG("Open kernel metadata");
                                ret = kernel_open_metadata(cmd_ctx->session->kernel_session,
-                                               cmd_ctx->session->path);
+                                               cmd_ctx->session->kernel_session->trace_path);
                                if (ret < 0) {
                                        ret = LTTCOMM_KERN_META_FAIL;
                                        goto error;
@@ -1877,16 +2223,16 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                                }
                        }
 
-                       DBG("Start kernel tracing");
-                       ret = kernel_start_session(cmd_ctx->session->kernel_session);
+                       ret = start_kernel_trace(cmd_ctx->session->kernel_session);
                        if (ret < 0) {
-                               ERR("Kernel start session failed");
                                ret = LTTCOMM_KERN_START_FAIL;
                                goto error;
                        }
 
-                       ret = start_kernel_trace(cmd_ctx->session->kernel_session);
+                       DBG("Start kernel tracing");
+                       ret = kernel_start_session(cmd_ctx->session->kernel_session);
                        if (ret < 0) {
+                               ERR("Kernel start session failed");
                                ret = LTTCOMM_KERN_START_FAIL;
                                goto error;
                        }
@@ -2062,7 +2408,7 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                        goto setup_error;
                }
 
-               DBG("Listing events (%ld events)", nb_event);
+               DBG("Listing events (%zu events)", nb_event);
 
                list_lttng_events(kchan,
                                (struct lttng_event *)(cmd_ctx->llm->payload));
@@ -2095,7 +2441,6 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                ret = LTTCOMM_OK;
                break;
        }
-
        case LTTNG_CALIBRATE:
        {
                /* Setup lttng message with no payload */
@@ -2125,6 +2470,43 @@ static int process_client_msg(struct command_ctx *cmd_ctx)
                ret = LTTCOMM_OK;
                break;
        }
+       case LTTNG_REGISTER_CONSUMER:
+       {
+               int sock;
+
+               /* Setup lttng message with no payload */
+               ret = setup_lttng_msg(cmd_ctx, 0);
+               if (ret < 0) {
+                       goto setup_error;
+               }
+
+               switch (cmd_ctx->lsm->domain.type) {
+               case LTTNG_DOMAIN_KERNEL:
+                       {
+                               /* Can't register a consumer if there is already one */
+                               if (cmd_ctx->session->kernel_session->consumer_fd != 0) {
+                                       ret = LTTCOMM_CONNECT_FAIL;
+                                       goto error;
+                               }
+
+                               sock = lttcomm_connect_unix_sock(cmd_ctx->lsm->u.reg.path);
+                               if (sock < 0) {
+                                       ret = LTTCOMM_CONNECT_FAIL;
+                                       goto error;
+                               }
+
+                               cmd_ctx->session->kernel_session->consumer_fd = sock;
+                               break;
+                       }
+               default:
+                       /* TODO: Userspace tracing */
+                       ret = LTTCOMM_NOT_IMPLEMENTED;
+                       goto error;
+               }
+
+               ret = LTTCOMM_OK;
+               break;
+       }
 
        default:
                /* Undefined command */
@@ -2442,13 +2824,15 @@ end:
 static int check_existing_daemon(void)
 {
        if (access(client_unix_sock_path, F_OK) < 0 &&
-           access(apps_unix_sock_path, F_OK) < 0)
+                       access(apps_unix_sock_path, F_OK) < 0) {
                return 0;
+       }
        /* Is there anybody out there ? */
-       if (lttng_session_daemon_alive())
+       if (lttng_session_daemon_alive()) {
                return -EEXIST;
-       else
+       } else {
                return 0;
+       }
 }
 
 /*
@@ -2509,6 +2893,14 @@ static int create_kernel_poll_pipe(void)
        return pipe2(kernel_poll_pipe, O_CLOEXEC);
 }
 
+/*
+ * Create the application command pipe to wake thread_manage_apps.
+ */
+static int create_apps_cmd_pipe(void)
+{
+       return pipe2(apps_cmd_pipe, O_CLOEXEC);
+}
+
 /*
  * Create the lttng run directory needed for all global sockets and pipe.
  */
@@ -2785,6 +3177,14 @@ int main(int argc, char **argv)
                goto exit;
        }
 
+       /* Setup the thread apps communication pipe. */
+       if ((ret = create_apps_cmd_pipe()) < 0) {
+               goto exit;
+       }
+
+       /* Init UST command queue. */
+       cds_wfq_init(&ust_cmd_queue.queue);
+
        /*
         * Get session list pointer. This pointer MUST NOT be free().
         * This list is statically declared in session.c
@@ -2792,23 +3192,40 @@ int main(int argc, char **argv)
        session_list_ptr = get_session_list();
 
        /* Create thread to manage the client socket */
-       ret = pthread_create(&client_thread, NULL, thread_manage_clients, (void *) NULL);
+       ret = pthread_create(&client_thread, NULL,
+                       thread_manage_clients, (void *) NULL);
        if (ret != 0) {
-               perror("pthread_create");
+               perror("pthread_create clients");
                goto exit_client;
        }
 
+       /* Create thread to dispatch registration */
+       ret = pthread_create(&dispatch_thread, NULL,
+                       thread_dispatch_ust_registration, (void *) NULL);
+       if (ret != 0) {
+               perror("pthread_create dispatch");
+               goto exit_dispatch;
+       }
+
+       /* Create thread to manage application registration. */
+       ret = pthread_create(&reg_apps_thread, NULL,
+                       thread_registration_apps, (void *) NULL);
+       if (ret != 0) {
+               perror("pthread_create registration");
+               goto exit_reg_apps;
+       }
+
        /* Create thread to manage application socket */
        ret = pthread_create(&apps_thread, NULL, thread_manage_apps, (void *) NULL);
        if (ret != 0) {
-               perror("pthread_create");
+               perror("pthread_create apps");
                goto exit_apps;
        }
 
        /* Create kernel thread to manage kernel event */
        ret = pthread_create(&kernel_thread, NULL, thread_manage_kernel, (void *) NULL);
        if (ret != 0) {
-               perror("pthread_create");
+               perror("pthread_create kernel");
                goto exit_kernel;
        }
 
@@ -2826,6 +3243,20 @@ exit_kernel:
        }
 
 exit_apps:
+       ret = pthread_join(reg_apps_thread, &status);
+       if (ret != 0) {
+               perror("pthread_join");
+               goto error;     /* join error, exit without cleanup */
+       }
+
+exit_reg_apps:
+       ret = pthread_join(dispatch_thread, &status);
+       if (ret != 0) {
+               perror("pthread_join");
+               goto error;     /* join error, exit without cleanup */
+       }
+
+exit_dispatch:
        ret = pthread_join(client_thread, &status);
        if (ret != 0) {
                perror("pthread_join");
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