NAME

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

SYNOPSIS

       #include <tracefs.h>

       struct tracefs_cpu *tracefs_cpu_open(struct tracefs_instance *instance,
                                            int cpu, bool nonblock);
       void tracefs_cpu_close(struct tracefs_cpu *tcpu);

       struct tracefs_cpu *tracefs_cpu_alloc_fd(int fd, int subbuf_size, bool nonblock);
       void tracefs_cpu_free_fd(struct tracefs_cpu *tcpu);

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.

RETURN VALUE

       The tracefs_cpu_open() returns 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

           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

           Steven Rostedt <rostedt@goodmis.org[1]>

REPORTING BUGS

       Report bugs to <linux-trace-devel@vger.kernel.org[2]>

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).

NOTES

        1. rostedt@goodmis.org
           mailto:rostedt@goodmis.org

        2. linux-trace-devel@vger.kernel.org
           mailto:linux-trace-devel@vger.kernel.org