From: David Goulet <david.goulet@polymtl.ca>
Date: Thu, 7 Jul 2011 14:29:19 +0000 (-0400)
Subject: Add detection of debugfs and kernel module loading
X-Git-Tag: v2.0-pre1~50
X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=b73401da87657682c2b51665a6fd1950f5c362f1;p=lttng-tools.git

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 af48cd92a..e87830211 100644
--- 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 0ab3ad9a7..205548bed 100644
--- 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) {