[PATCH 6/9] libtracefs man pages: APIs for working with files in trace instances.

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

Documented APIs:
tracefs_file_exists()
tracefs_dir_exists()
tracefs_instance_get_file()
tracefs_instance_get_dir()
tracefs_instance_file_write()
tracefs_instance_file_read()

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 Documentation/libtracefs-instances-files.txt | 157 +++++++++++++++++++
 1 file changed, 157 insertions(+)
 create mode 100644 Documentation/libtracefs-instances-files.txt

diff --git a/Documentation/libtracefs-instances-files.txt b/Documentation/libtracefs-instances-files.txt
new file mode 100644
index 0000000..f1e9707
--- /dev/null
+++ b/Documentation/libtracefs-instances-files.txt
@@ -0,0 +1,157 @@
+libtracefs(3)
+=============
+
+NAME
+----
+tracefs_file_exists, tracefs_dir_exists, tracefs_instance_get_file,
+tracefs_instance_get_dir, tracefs_instance_file_write,
+tracefs_instance_file_read - Work with files in tracing instances.
+
+SYNOPSIS
+--------
+[verse]
+--
+*#include <tracefs.h>*
+
+bool *tracefs_file_exists*(struct tracefs_instance pass:[*]_instance_, char pass:[*]_name_);
+bool *tracefs_dir_exists*(struct tracefs_instance pass:[*]_instance_, char pass:[*]_name_);
+char pass:[*]*tracefs_instance_get_file*(struct tracefs_instance pass:[*]_instance_, const char pass:[*]_file_);
+char pass:[*]*tracefs_instance_get_dir*(struct tracefs_instance pass:[*]_instance_);
+int *tracefs_instance_file_write*(struct tracefs_instance pass:[*]_instance_, const char pass:[*]_file_, const char pass:[*]_str_);
+char pass:[*]*tracefs_instance_file_read*(struct tracefs_instance pass:[*]_instance_, char pass:[*]_file_, int pass:[*]_psize_);
+
+--
+
+DESCRIPTION
+-----------
+This set of APIs can be used to work with trace files in all trace instances.
+All they have _instance_ argument, to limit the scope on the given trace _instance_ only.
+If _instance_ is NULL, the scope is limited to the main trace instance.
+
+The _tracefs_file_exists()_ function checks if a file with _name_ exists in _instance_.
+
+The _tracefs_dir_exists()_ function checks if a directory with _name_ exists in _instance_.
+
+The _tracefs_instance_get_file()_ function returns the full path of the file with
+given _name_ in _instance_.
+
+The _tracefs_instance_get_dir()_ function  returns the full path of the directory with
+given _name_ in _instance_.
+
+The _tracefs_instance_file_write()_ function writes a string _str_ in a _file_ from
+the given _instance_, without the terminating NULL character.
+
+The _tracefs_instance_file_read()_ function reads the content of a _file_  from
+the given _instance_.
+
+RETURN VALUE
+------------
+The _tracefs_file_exists()_ and  _tracefs_dir_exists()_ functions return true if the
+file / directory exist in the given instance or false if they do not exist.
+
+The _tracefs_instance_get_file()_ and _tracefs_instance_get_dir()_ functions return
+a string or NULL in case of an error. The returned string must be freed with
+_tracefs_put_tracing_file()_.
+
+The _tracefs_instance_file_write()_ function returns the number of written bytes,
+or -1 in case of an error.
+
+The _tracefs_instance_file_read()_ function returns a pointer to a NULL terminated
+string, read from the file, or NULL in case of an error. The returned string must
+be freed with free().
+
+EXAMPLE
+-------
+[source,c]
+--
+#include <tracefs.h>
+
+struct tracefs_instance *inst = tracefs_instance_create("foo");
+	if (!inst) {
+		/* Error creating a new trace instance */
+		...
+	}
+
+	if (tracefs_file_exists(inst,"trace_clock")) {
+		/* The instance foo supports trace clock */
+		char *path, *clock;
+		int size;
+
+		path =  = tracefs_instance_get_file(inst, "trace_clock")
+		if (!path) {
+			/* Error getting the path to trace_clock file in instance foo */
+			...
+		}
+		...
+		tracefs_put_tracing_file(path);
+
+		clock = tracefs_instance_file_read(inst, "trace_clock", &size);
+		if (!clock) {
+			/* Failed to read trace_clock file in instance foo */
+			...
+		}
+		...
+		free(clock);
+
+		if (tracefs_instance_file_write(inst, "trace_clock", "global") != strlen("global")) {
+			/* Failed to set gloabl trace clock in instance foo */
+			...
+		}
+	} else {
+		/* The instance foo does not support trace clock */
+	}
+
+	if (tracefs_dir_exists(inst,"options")) {
+		/* The instance foo supports trace options */
+		char *path = tracefs_instance_get_file(inst, "options");
+		if (!path) {
+			/* Error getting the path to options directory in instance foo */
+			...
+		}
+
+		tracefs_put_tracing_file(path);
+	} else {
+		/* The instance foo does not support trace options */
+	}
+
+	...
+
+	if (tracefs_instance_is_new(inst))
+		tracefs_instance_destroy(inst);
+	else
+		tracefs_instance_free(inst);
+--
+FILES
+-----
+[verse]
+--
+*tracefs.h*
+	Header file to include in order to have access to the library APIs.
+*-ltracefs*
+	Linker switch to add when building a program that uses the library.
+--
+
+SEE ALSO
+--------
+_libtracefs(3)_,
+_libtraceevent(3)_,
+_trace-cmd(1)_
+
+AUTHOR
+------
+[verse]
+--
+*Steven Rostedt* <rostedt@goodmis.org>
+*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
+--
+REPORTING BUGS
+--------------
+Report bugs to  <linux-trace-devel@vger.kernel.org>
+
+LICENSE
+-------
+libtracefs is Free Software licensed under the GNU LGPL 2.1
+
+RESOURCES
+---------
+https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
\ No newline at end of file
-- 
2.28.0