[PATCH 3/5] libtracefs: Add information about top tracing directory in instance structure

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx>]

There are use cases, where the library could be used with non default
system trace directory - for example a partial copy of a system trace
directory from another machine. More flexibility is added to the tracefs
library, to handle these use cases. The full path to the system trace
directory is added in the instance structure and is used to get trace
files from that instance.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
---
 src/tracefs-instance.c | 80 ++++++++++++++++++++++++++----------------
 1 file changed, 49 insertions(+), 31 deletions(-)

diff --git a/src/tracefs-instance.c b/src/tracefs-instance.c
index b5f8298..468da1b 100644
--- a/src/tracefs-instance.c
+++ b/src/tracefs-instance.c
@@ -20,30 +20,43 @@
 
 #define FLAG_INSTANCE_NEWLY_CREATED	(1 << 0)
 struct tracefs_instance {
+	char	*trace_dir;
 	char	*name;
 	int	flags;
 };
 
 /**
  * instance_alloc - allocate a new ftrace instance
+ * @trace_dir - Full path to the tracing directory, where the instance is
  * @name: The name of the instance (instance will point to this)
  *
  * Returns a newly allocated instance, or NULL in case of an error.
  */
-static struct tracefs_instance *instance_alloc(const char *name)
+static struct tracefs_instance *instance_alloc(const char *trace_dir, const char *name)
 {
 	struct tracefs_instance *instance;
 
 	instance = calloc(1, sizeof(*instance));
-	if (instance && name) {
+	if (!instance)
+		goto error;
+	instance->trace_dir = strdup(trace_dir);
+	if (!instance->trace_dir)
+		goto error;
+	if (name) {
 		instance->name = strdup(name);
-		if (!instance->name) {
-			free(instance);
-			instance = NULL;
-		}
+		if (!instance->name)
+			goto error;
 	}
 
 	return instance;
+
+error:
+	if (instance) {
+		free(instance->name);
+		free(instance->trace_dir);
+		free(instance);
+	}
+	return NULL;
 }
 
 /**
@@ -56,6 +69,7 @@ void tracefs_instance_free(struct tracefs_instance *instance)
 {
 	if (!instance)
 		return;
+	free(instance->trace_dir);
 	free(instance->name);
 	free(instance);
 }
@@ -105,12 +119,16 @@ bool tracefs_instance_is_new(struct tracefs_instance *instance)
 struct tracefs_instance *tracefs_instance_create(const char *name)
 {
 	struct tracefs_instance *inst = NULL;
+	char *path = NULL;
+	const char *tdir;
 	struct stat st;
 	mode_t mode;
-	char *path;
 	int ret;
 
-	inst = instance_alloc(name);
+	tdir = tracefs_tracing_dir();
+	if (!tdir)
+		return NULL;
+	inst = instance_alloc(tdir, name);
 	if (!inst)
 		return NULL;
 
@@ -170,18 +188,18 @@ int tracefs_instance_destroy(struct tracefs_instance *instance)
 char *
 tracefs_instance_get_file(struct tracefs_instance *instance, const char *file)
 {
-	char *path;
-	char *buf;
+	char *path = NULL;
 	int ret;
 
-	if (instance && instance->name) {
-		ret = asprintf(&buf, "instances/%s/%s", instance->name, file);
-		if (ret < 0)
-			return NULL;
-		path = tracefs_get_tracing_file(buf);
-		free(buf);
-	} else
-		path = tracefs_get_tracing_file(file);
+	if (!instance)
+		return tracefs_get_tracing_file(file);
+	if (!instance->name)
+		ret = asprintf(&path, "%s/%s", instance->trace_dir, file);
+	else
+		ret = asprintf(&path, "%s/instances/%s/%s",
+			       instance->trace_dir, instance->name, file);
+	if (ret < 0)
+		return NULL;
 
 	return path;
 }
@@ -196,21 +214,21 @@ tracefs_instance_get_file(struct tracefs_instance *instance, const char *file)
  */
 char *tracefs_instance_get_dir(struct tracefs_instance *instance)
 {
-	char *buf;
-	char *path;
+	char *path = NULL;
 	int ret;
 
-	if (instance && instance->name) {
-		ret = asprintf(&buf, "instances/%s", instance->name);
-		if (ret < 0) {
-			warning("Failed to allocate path for instance %s",
-				 instance->name);
-			return NULL;
-		}
-		path = tracefs_get_tracing_file(buf);
-		free(buf);
-	} else
-		path = trace_find_tracing_dir();
+	if (!instance) /* Top instance of default system trace directory */
+		return trace_find_tracing_dir();
+
+	if (!instance->name)
+		return strdup(instance->trace_dir);
+
+	ret = asprintf(&path, "%s/instances/%s", instance->trace_dir, instance->name);
+	if (ret < 0) {
+		warning("Failed to allocate path for instance %s",
+			 instance->name);
+		return NULL;
+	}
 
 	return path;
 }
-- 
2.29.2