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LIBTRACEEVENT(3) libtraceevent Manual LIBTRACEEVENT(3)
tep_register_print_function, tep_unregister_print_function - Registers / Unregisters a helper function.
#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);
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.
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.
Some events have internal functions calls, that appear in the print format output. For example "tracefs/events/i915/g4x_wm/format" has: print fmt: "pipe %c, frame=%u, scanline=%u, wm %d/%d/%d, sr %s/%d/%d/%d, hpll %s/%d/%d/%d, fbc %s", ((REC->pipe) + 'A'), REC->frame, REC->scanline, REC->primary, REC->sprite, REC->cursor, yesno(REC->cxsr), REC->sr_plane, REC->sr_cursor, REC->sr_fbc, yesno(REC->hpll), REC->hpll_plane, REC->hpll_cursor, REC->hpll_fbc, yesno(REC->fbc) Notice the call to function yesno() in the print arguments. In the kernel context, this function has the following implementation: static const char *yesno(int x) { static const char *yes = "yes"; static const char *no = "no"; return x ? yes : no; } 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(): #include <event-parse.h> #include <trace-seq.h> ... struct tep_handle *tep = tep_alloc(); ... static const char *yes_no_helper(int x) { return x ? "yes" : "no"; } ... if ( tep_register_print_function(tep, yes_no_helper, TEP_FUNC_ARG_STRING, "yesno", TEP_FUNC_ARG_INT, TEP_FUNC_ARG_VOID) != 0) { /* Failed to register yes_no_helper function */ } /* Now, when the event parser encounters this yesno() function, it will know how to handle it. */ ... if (tep_unregister_print_function(tep, yes_no_helper, "yesno") != 0) { /* Failed to unregister yes_no_helper function */ }
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.
libtraceevent(3), trace-cmd(1)
Steven Rostedt <[email protected][1]>, author of libtraceevent. Tzvetomir Stoyanov <[email protected][2]>, author of this man page.
Report bugs to <[email protected][3]>
libtraceevent is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/
1. [email protected] mailto:[email protected] 2. [email protected] mailto:[email protected] 3. [email protected] mailto:[email protected]
This page is part of the libtraceevent (Linux kernel trace event
library) project. Information about the project can be found at
⟨https://www.trace-cmd.org/⟩. If you have a bug report for this
manual page, see ⟨https://www.trace-cmd.org/⟩. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git⟩
on 2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-05-17.) If you
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libtraceevent 1.7.3 09/24/2023 LIBTRACEEVENT(3)