SYNOPSIS
#include <event-parse.h> enum tep_func_arg_type { TEP_FUNC_ARG_VOID, TEP_FUNC_ARG_INT, TEP_FUNC_ARG_LONG, TEP_FUNC_ARG_STRING, TEP_FUNC_ARG_PTR, TEP_FUNC_ARG_MAX_TYPES }; typedef unsigned long long (*tep_func_handler)(struct trace_seq *s, unsigned long long *args); int tep_register_print_function(struct tep_handle *tep, tep_func_handler func, enum tep_func_arg_type ret_type, char *name, …); int tep_unregister_print_function(struct tep_handle *tep, tep_func_handler func, char *name);
DESCRIPTION
Some events may have helper functions in the print format arguments. This allows a plugin to dynamically create a way to process one of these functions.
The tep_register_print_function() registers such helper function. The tep argument is the trace event parser context. The func argument is a pointer to the helper function. The ret_type argument is the return type of the helper function, value from the tep_func_arg_type enum. The name is the name of the helper function, as seen in the print format arguments. The … is a variable list of tep_func_arg_type enums, the func function arguments. This list must end with TEP_FUNC_ARG_VOID. See EXAMPLE section.
The tep_unregister_print_function() unregisters a helper function, previously registered with tep_register_print_function(). The tep argument is the trace event parser context. The func and name arguments are the same, used when the helper function was registered.
The tep_func_handler is the type of the helper function. The s argument is the trace sequence, it can be used to create a custom string. The args is a list of arguments, defined when the helper function was registered.
RETURN VALUE
The tep_register_print_function() function returns 0 in case of success. In case of an error, TEP_ERRNO_… code is returned.
The tep_unregister_print_function() returns 0 in case of success, or -1 in case of an error.
EXAMPLE
Some events have internal functions calls, that appear in the print format output. For example "tracefs/events/i915/g4x_wm/format" has:
Notice the call to function yesno() in the print arguments. In the kernel context, this function has the following implementation:
The user space event parser has no idea how to handle this yesno() function. The tep_register_print_function() API can be used to register a user space helper function, mapped to the kernel’s yesno():
FILES
event-parse.h Header file to include in order to have access to the library APIs. trace-seq.h Header file to include in order to have access to trace sequences related APIs. Trace sequences are used to allow a function to call several other functions to create a string of data to use. -ltraceevent Linker switch to add when building a program that uses the library.
SEE ALSO
libtraceevent(3), trace-cmd(1)
AUTHOR
Steven Rostedt <rostedt@goodmis.org>, author of libtraceevent. Tzvetomir Stoyanov <tz.stoyanov@gmail.com>, author of this man page.
REPORTING BUGS
Report bugs to <linux-trace-devel@vger.kernel.org>
LICENSE
libtraceevent is Free Software licensed under the GNU LGPL 2.1