Add detection of debugfs and kernel module loading

The session daemon now detects the path of the debugfs mount point or
create and mount it at a default location (/mnt/debugfs).

Then, the kernel module are loaded automatically, if present, and the
kernel tracer fd is opened at the previous detected debugfs path.

The kernel module list is hardcoded for now.

NOTE: There is no module unload at the session daemon cleanup. This is
to avoid removing tracing capabilities when a trace is ongoing and
written to disk.

Signed-off-by: David Goulet <david.goulet@polymtl.ca>

diff --git a/ltt-sessiond/ltt-sessiond.h b/ltt-sessiond/ltt-sessiond.h
index af48cd92a39c16b5da4e314056c6868705b2e707..e878302115d95ade6040609f64c391beb1630ac4 100644 (file)
--- a/ltt-sessiond/ltt-sessiond.h
+++ b/ltt-sessiond/ltt-sessiond.h
@@ -24,10 +24,27 @@
 #define DEFAULT_GLOBAL_APPS_PIPE       DEFAULT_UST_SOCK_DIR "/global"
 #define DEFAULT_TRACE_OUTPUT        DEFAULT_HOME_DIR "/lttng"
 
-/*
- * Kernel tracer defines
- */
-#define DEFAULT_KERNEL_TRACER_PATH                     "/mnt/debugfs/lttng"
+/* LTTng kernel tracer modules list */
+const char *kernel_modules_list[] = {
+       "lib-ring-buffer",
+       "ltt-relay",
+       "ltt-ring-buffer-client-discard",
+       "ltt-ring-buffer-client-overwrite",
+       "ltt-ring-buffer-metadata-client",
+       "ltt-ring-buffer-client-mmap-discard",
+       "ltt-ring-buffer-client-mmap-overwrite",
+       "ltt-ring-buffer-metadata-mmap-client",
+       "lttng-ftrace",
+       "lttng-kprobes",
+       "lttng-probe-block",
+       "lttng-probe-irq",
+       "lttng-probe-kvm",
+       "lttng-probe-lttng",
+       "lttng-probe-sched",
+       "lttng-probe-syscalls",
+       "lttng-types",
+       NULL,
+};
 
 extern const char default_home_dir[],
        default_tracing_group[],

diff --git a/ltt-sessiond/main.c b/ltt-sessiond/main.c
index 0ab3ad9a73300221092babcbbd3671ea8b5983b5..205548bed3cecad8720ca395ceedfc2bd614dc9c 100644 (file)
--- a/ltt-sessiond/main.c
+++ b/ltt-sessiond/main.c
@@ -28,6 +28,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/ipc.h>
+#include <sys/mount.h>
 #include <sys/shm.h>
 #include <sys/socket.h>
 #include <sys/stat.h>
@@ -641,6 +642,58 @@ error:
        return ret;
 }
 
+/*
+ *  modprobe_kernel_modules
+ */
+static int modprobe_kernel_modules(void)
+{
+       int ret = 0, i = 0;
+       char modprobe[256];
+
+       while (kernel_modules_list[i] != NULL) {
+               ret = snprintf(modprobe, sizeof(modprobe), "/sbin/modprobe %s",
+                               kernel_modules_list[i]);
+               if (ret < 0) {
+                       perror("snprintf modprobe");
+                       goto error;
+               }
+               ret = system(modprobe);
+               if (ret < 0) {
+                       ERR("Unable to load module %s", kernel_modules_list[i]);
+               }
+               DBG("Modprobe successfully %s", kernel_modules_list[i]);
+               i++;
+       }
+
+error:
+       return ret;
+}
+
+/*
+ *  mount_debugfs
+ */
+static int mount_debugfs(char *path)
+{
+       int ret;
+       char *type = "debugfs";
+
+       ret = mkdir_recursive(path, S_IRWXU | S_IRWXG);
+       if (ret < 0) {
+               goto error;
+       }
+
+       ret = mount(type, path, type, 0, NULL);
+       if (ret < 0) {
+               perror("mount debugfs");
+               goto error;
+       }
+
+       DBG("Mounted debugfs successfully at %s", path);
+
+error:
+       return ret;
+}
+
 /*
  *  init_kernel_tracer
  *
@@ -648,14 +701,80 @@ error:
  */
 static void init_kernel_tracer(void)
 {
-       /* Set the global kernel tracer fd */
-       kernel_tracer_fd = open(DEFAULT_KERNEL_TRACER_PATH, O_RDWR);
+       int ret;
+       char *proc_mounts = "/proc/mounts";
+       char line[256];
+       char *debugfs_path = NULL, *lttng_path;
+       FILE *fp;
+
+       /* Detect debugfs */
+       fp = fopen(proc_mounts, "r");
+       if (fp == NULL) {
+               ERR("Unable to probe %s", proc_mounts);
+               goto error;
+       }
+
+       while (fgets(line, sizeof(line), fp) != NULL) {
+               if (strstr(line, "debugfs") != NULL) {
+                       /* Remove first string */
+                       strtok(line, " ");
+                       /* Dup string here so we can reuse line later on */
+                       debugfs_path = strdup(strtok(NULL, " "));
+                       DBG("Got debugfs path : %s", debugfs_path);
+                       break;
+               }
+       }
+
+       fclose(fp);
+
+       /* Mount debugfs if needded */
+       if (debugfs_path == NULL) {
+               ret = asprintf(&debugfs_path, "/mnt/debugfs");
+               if (ret < 0) {
+                       perror("asprintf debugfs path");
+                       goto error;
+               }
+               ret = mount_debugfs(debugfs_path);
+               if (ret < 0) {
+                       goto error;
+               }
+       }
+
+       /* Modprobe lttng kernel modules */
+       ret = modprobe_kernel_modules();
+       if (ret < 0) {
+               goto error;
+       }
+
+       /* Setup lttng kernel path */
+       ret = asprintf(&lttng_path, "%s/lttng", debugfs_path);
+       if (ret < 0) {
+               perror("asprintf lttng path");
+               goto error;
+       }
+
+       /* Open debugfs lttng */
+       kernel_tracer_fd = open(lttng_path, O_RDWR);
        if (kernel_tracer_fd < 0) {
-               WARN("No kernel tracer available");
-               kernel_tracer_fd = 0;
+               DBG("Failed to open %s", lttng_path);
+               goto error;
        }
 
+       free(lttng_path);
+       free(debugfs_path);
        DBG("Kernel tracer fd %d", kernel_tracer_fd);
+       return;
+
+error:
+       if (lttng_path) {
+               free(lttng_path);
+       }
+       if (debugfs_path) {
+               free(debugfs_path);
+       }
+       WARN("No kernel tracer available");
+       kernel_tracer_fd = 0;
+       return;
 }
 
 /*
@@ -1995,7 +2114,6 @@ int main(int argc, char **argv)
        /* Check if daemon is UID = 0 */
        is_root = !getuid();
 
-       /* Set all sockets path */
        if (is_root) {
                ret = create_lttng_rundir();
                if (ret < 0) {