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Diffstat (limited to 'Documentation/libtraceevent-reg_print_func.txt')
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diff --git a/Documentation/libtraceevent-reg_print_func.txt b/Documentation/libtraceevent-reg_print_func.txt new file mode 100644 index 0000000..b3c8491 --- /dev/null +++ b/Documentation/libtraceevent-reg_print_func.txt @@ -0,0 +1,155 @@ +libtraceevent(3) +================ + +NAME +---- +tep_register_print_function,tep_unregister_print_function - +Registers / Unregisters a helper function. + +SYNOPSIS +-------- +[verse] +-- +*#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 (*pass:[*]tep_func_handler*)(struct trace_seq pass:[*]s, unsigned long long pass:[*]args); + +int *tep_register_print_function*(struct tep_handle pass:[*]_tep_, tep_func_handler _func_, enum tep_func_arg_type _ret_type_, char pass:[*]_name_, _..._); +int *tep_unregister_print_function*(struct tep_handle pass:[*]_tep_, tep_func_handler _func_, char pass:[*]_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: +[source,c] +-- +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: +[source,c] +-- +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()*: +[source,c] +-- +#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 */ + } +-- + +FILES +----- +[verse] +-- +*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 +------ +[verse] +-- +*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 + +RESOURCES +--------- +https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/ |