libtracefs(3)
=============

NAME
----
tracefs_cpu_open, tracefs_cpu_close, tracefs_cpu_alloc_fd, tracefs_cpu_free_fd, tracefs_cpu_snapshot_open - Opening trace_pipe_raw data for reading

SYNOPSIS
--------
[verse]
--
*#include <tracefs.h>*

struct tracefs_cpu pass:[*]*tracefs_cpu_open*(struct tracefs_instance pass:[*]_instance_,
				     int _cpu_, bool _nonblock_);
void *tracefs_cpu_close*(struct tracefs_cpu pass:[*]_tcpu_);

struct tracefs_cpu pass:[*]*tracefs_cpu_alloc_fd*(int _fd_, int _subbuf_size_, bool _nonblock_);
void *tracefs_cpu_free_fd*(struct tracefs_cpu pass:[*]_tcpu_);

struct tracefs_cpu pass:[*]*tracefs_cpu_snapshot_open*(struct tracefs_instance pass:[*]_instance_,
					     int _cpu_, bool _nonblock_);
--

DESCRIPTION
-----------
This set of APIs can be used to open the raw data from the trace_pipe_raw
files in the tracefs file system in oder to read them with the *tracefs_cpu_read*(3)
functions.

The *tracefs_cpu_open()* creates a descriptor that can read the tracefs
trace_pipe_raw file for a given _cpu_ in a given _instance_. If _instance_ is
NULL than the toplevel trace_pipe_raw file is used.

The *tracefs_cpu_close()* closes all the file descriptors associated to the trace_pipe_raw
opened by *tracefs_cpu_open()*.

The *tracefs_cpu_alloc_fd()* will create a tracefs_cpu descriptor from an existing
file descriptor _fd_. This is useful to use when connecting to a socket or pipe where
the other end is feeding raw tracing data in the same format as the trace_pipe_raw
file would (like in guest to host tracing). The caller is responsible for determining
the _subbuf_size_ that will be used to break up the sub-buffers being read by the
file descriptor. The _nonblock_ is treated the same as the same parameter in
*tracefs_cpu_open()*.

The *tracefs_cpu_free_fd()* is used to free the descriptor returned by *tracefs_cpu_alloc_fd()*.
It does all the clean up that *tracefs_cpu_close()* performs, and that could also be
used to free up the descriptor created by *tracefs_cpu_alloc_fd()* but will also close
the file descriptor passed in. Note that *tracefs_cpu_free_fd()* should not be used
on the descriptor returned by *tracefs_cpu_open()* as it will not close the file descriptor
created by it.

The *tracefs_cpu_snapshot_open()* is similar to *tracefs_cpu_open()* except that it
opens the snapshot buffer (see *tracefs_snapshot_snap*(3)). The snapshot buffer
does not have a writer to it, it is only created by a snapshot action that swaps
the current ring buffer with the snapshot buffer. The _nonblock_, when false, acts a little
differently here too. Reads are not affected by the "buffer_percent" file. If the
snapshot buffer is empty, it will block until a new snapshot happens.

RETURN VALUE
------------
The *tracefs_cpu_open()* and *tracefs_cpu_snapshot_open() both return a struct
tracefs_cpu descriptor that can be used by the other functions or NULL on error.

The *tracefs_cpu_alloc_fd()* returns a struct tracefs_cpu descriptor that can
be used by the *tracefs_cpu_read*(3) related functions, where the descriptor
will be reading the passed in _fd_ file descriptor.

EXAMPLE
-------
See *tracefs_cpu_read*(3) for an example.

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>
--
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/

COPYING
-------
Copyright \(C) 2022 Google, Inc. Free use of this software is granted under
the terms of the GNU Public License (GPL).
