libtraceevent-reg_print_func.txt (4744B)
1libtraceevent(3) 2================ 3 4NAME 5---- 6tep_register_print_function,tep_unregister_print_function - 7Registers / Unregisters a helper function. 8 9SYNOPSIS 10-------- 11[verse] 12-- 13*#include <event-parse.h>* 14 15enum *tep_func_arg_type* { 16 TEP_FUNC_ARG_VOID, 17 TEP_FUNC_ARG_INT, 18 TEP_FUNC_ARG_LONG, 19 TEP_FUNC_ARG_STRING, 20 TEP_FUNC_ARG_PTR, 21 TEP_FUNC_ARG_MAX_TYPES 22}; 23 24typedef unsigned long long (*pass:[*]tep_func_handler*)(struct trace_seq pass:[*]s, unsigned long long pass:[*]args); 25 26int *tep_register_print_function*(struct tep_handle pass:[*]_tep_, tep_func_handler _func_, enum tep_func_arg_type _ret_type_, char pass:[*]_name_, _..._); 27int *tep_unregister_print_function*(struct tep_handle pass:[*]_tep_, tep_func_handler _func_, char pass:[*]_name_); 28-- 29 30DESCRIPTION 31----------- 32Some events may have helper functions in the print format arguments. 33This allows a plugin to dynamically create a way to process one of 34these functions. 35 36The _tep_register_print_function()_ registers such helper function. The _tep_ 37argument is the trace event parser context. The _func_ argument is a pointer 38to the helper function. The _ret_type_ argument is the return type of the 39helper function, value from the _tep_func_arg_type_ enum. The _name_ is the name 40of the helper function, as seen in the print format arguments. The _..._ is a 41variable list of _tep_func_arg_type_ enums, the _func_ function arguments. 42This list must end with _TEP_FUNC_ARG_VOID_. See 'EXAMPLE' section. 43 44The _tep_unregister_print_function()_ unregisters a helper function, previously 45registered with _tep_register_print_function()_. The _tep_ argument is the 46trace event parser context. The _func_ and _name_ arguments are the same, used 47when the helper function was registered. 48 49The _tep_func_handler_ is the type of the helper function. The _s_ argument is 50the trace sequence, it can be used to create a custom string. 51The _args_ is a list of arguments, defined when the helper function was 52registered. 53 54RETURN VALUE 55------------ 56The _tep_register_print_function()_ function returns 0 in case of success. 57In case of an error, TEP_ERRNO_... code is returned. 58 59The _tep_unregister_print_function()_ returns 0 in case of success, or -1 in 60case of an error. 61 62EXAMPLE 63------- 64Some events have internal functions calls, that appear in the print format 65output. For example "tracefs/events/i915/g4x_wm/format" has: 66[source,c] 67-- 68print fmt: "pipe %c, frame=%u, scanline=%u, wm %d/%d/%d, sr %s/%d/%d/%d, hpll %s/%d/%d/%d, fbc %s", 69 ((REC->pipe) + 'A'), REC->frame, REC->scanline, REC->primary, 70 REC->sprite, REC->cursor, yesno(REC->cxsr), REC->sr_plane, 71 REC->sr_cursor, REC->sr_fbc, yesno(REC->hpll), REC->hpll_plane, 72 REC->hpll_cursor, REC->hpll_fbc, yesno(REC->fbc) 73-- 74Notice the call to function _yesno()_ in the print arguments. In the kernel 75context, this function has the following implementation: 76[source,c] 77-- 78static const char *yesno(int x) 79{ 80 static const char *yes = "yes"; 81 static const char *no = "no"; 82 83 return x ? yes : no; 84} 85-- 86The user space event parser has no idea how to handle this _yesno()_ function. 87The _tep_register_print_function()_ API can be used to register a user space 88helper function, mapped to the kernel's _yesno()_: 89[source,c] 90-- 91#include <event-parse.h> 92#include <trace-seq.h> 93... 94struct tep_handle *tep = tep_alloc(); 95... 96static const char *yes_no_helper(int x) 97{ 98 return x ? "yes" : "no"; 99} 100... 101 if ( tep_register_print_function(tep, 102 yes_no_helper, 103 TEP_FUNC_ARG_STRING, 104 "yesno", 105 TEP_FUNC_ARG_INT, 106 TEP_FUNC_ARG_VOID) != 0) { 107 /* Failed to register yes_no_helper function */ 108 } 109 110/* 111 Now, when the event parser encounters this yesno() function, it will know 112 how to handle it. 113*/ 114... 115 if (tep_unregister_print_function(tep, yes_no_helper, "yesno") != 0) { 116 /* Failed to unregister yes_no_helper function */ 117 } 118-- 119 120FILES 121----- 122[verse] 123-- 124*event-parse.h* 125 Header file to include in order to have access to the library APIs. 126*trace-seq.h* 127 Header file to include in order to have access to trace sequences 128 related APIs. Trace sequences are used to allow a function to call 129 several other functions to create a string of data to use. 130*-ltraceevent* 131 Linker switch to add when building a program that uses the library. 132-- 133 134SEE ALSO 135-------- 136_libtraceevent(3)_, _trace-cmd(1)_ 137 138AUTHOR 139------ 140[verse] 141-- 142*Steven Rostedt* <rostedt@goodmis.org>, author of *libtraceevent*. 143*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>, author of this man page. 144-- 145REPORTING BUGS 146-------------- 147Report bugs to <linux-trace-devel@vger.kernel.org> 148 149LICENSE 150------- 151libtraceevent is Free Software licensed under the GNU LGPL 2.1 152 153RESOURCES 154--------- 155https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git