156 lines
4.6 KiB
Plaintext
156 lines
4.6 KiB
Plaintext
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libtraceevent(3)
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================
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NAME
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----
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tep_register_print_function,tep_unregister_print_function -
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Registers / Unregisters a helper function.
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SYNOPSIS
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--------
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[verse]
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--
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*#include <event-parse.h>*
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enum *tep_func_arg_type* {
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TEP_FUNC_ARG_VOID,
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TEP_FUNC_ARG_INT,
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TEP_FUNC_ARG_LONG,
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TEP_FUNC_ARG_STRING,
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TEP_FUNC_ARG_PTR,
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TEP_FUNC_ARG_MAX_TYPES
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};
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typedef unsigned long long (*pass:[*]tep_func_handler*)(struct trace_seq pass:[*]s, unsigned long long pass:[*]args);
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int *tep_register_print_function*(struct tep_handle pass:[*]_tep_, tep_func_handler _func_, enum tep_func_arg_type _ret_type_, char pass:[*]_name_, _..._);
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int *tep_unregister_print_function*(struct tep_handle pass:[*]_tep_, tep_func_handler _func_, char pass:[*]_name_);
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--
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DESCRIPTION
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-----------
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Some events may have helper functions in the print format arguments.
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This allows a plugin to dynamically create a way to process one of
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these functions.
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The _tep_register_print_function()_ registers such helper function. The _tep_
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argument is the trace event parser context. The _func_ argument is a pointer
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to the helper function. The _ret_type_ argument is the return type of the
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helper function, value from the _tep_func_arg_type_ enum. The _name_ is the name
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of the helper function, as seen in the print format arguments. The _..._ is a
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variable list of _tep_func_arg_type_ enums, the _func_ function arguments.
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This list must end with _TEP_FUNC_ARG_VOID_. See 'EXAMPLE' section.
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The _tep_unregister_print_function()_ unregisters a helper function, previously
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registered with _tep_register_print_function()_. The _tep_ argument is the
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trace event parser context. The _func_ and _name_ arguments are the same, used
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when the helper function was registered.
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The _tep_func_handler_ is the type of the helper function. The _s_ argument is
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the trace sequence, it can be used to create a custom string.
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The _args_ is a list of arguments, defined when the helper function was
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registered.
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RETURN VALUE
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------------
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The _tep_register_print_function()_ function returns 0 in case of success.
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In case of an error, TEP_ERRNO_... code is returned.
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The _tep_unregister_print_function()_ returns 0 in case of success, or -1 in
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case of an error.
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EXAMPLE
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-------
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Some events have internal functions calls, that appear in the print format
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output. For example "tracefs/events/i915/g4x_wm/format" has:
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[source,c]
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--
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print fmt: "pipe %c, frame=%u, scanline=%u, wm %d/%d/%d, sr %s/%d/%d/%d, hpll %s/%d/%d/%d, fbc %s",
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((REC->pipe) + 'A'), REC->frame, REC->scanline, REC->primary,
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REC->sprite, REC->cursor, yesno(REC->cxsr), REC->sr_plane,
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REC->sr_cursor, REC->sr_fbc, yesno(REC->hpll), REC->hpll_plane,
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REC->hpll_cursor, REC->hpll_fbc, yesno(REC->fbc)
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--
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Notice the call to function _yesno()_ in the print arguments. In the kernel
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context, this function has the following implementation:
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[source,c]
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--
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static const char *yesno(int x)
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{
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static const char *yes = "yes";
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static const char *no = "no";
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return x ? yes : no;
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}
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--
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The user space event parser has no idea how to handle this _yesno()_ function.
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The _tep_register_print_function()_ API can be used to register a user space
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helper function, mapped to the kernel's _yesno()_:
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[source,c]
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--
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#include <event-parse.h>
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#include <trace-seq.h>
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...
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struct tep_handle *tep = tep_alloc();
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...
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static const char *yes_no_helper(int x)
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{
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return x ? "yes" : "no";
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}
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...
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if ( tep_register_print_function(tep,
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yes_no_helper,
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TEP_FUNC_ARG_STRING,
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"yesno",
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TEP_FUNC_ARG_INT,
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TEP_FUNC_ARG_VOID) != 0) {
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/* Failed to register yes_no_helper function */
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}
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/*
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Now, when the event parser encounters this yesno() function, it will know
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how to handle it.
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*/
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...
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if (tep_unregister_print_function(tep, yes_no_helper, "yesno") != 0) {
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/* Failed to unregister yes_no_helper function */
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}
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--
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FILES
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-----
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[verse]
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--
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*event-parse.h*
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Header file to include in order to have access to the library APIs.
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*trace-seq.h*
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Header file to include in order to have access to trace sequences
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related APIs. Trace sequences are used to allow a function to call
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several other functions to create a string of data to use.
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*-ltraceevent*
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Linker switch to add when building a program that uses the library.
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--
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SEE ALSO
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--------
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_libtraceevent(3)_, _trace-cmd(1)_
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AUTHOR
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------
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[verse]
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--
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*Steven Rostedt* <rostedt@goodmis.org>, author of *libtraceevent*.
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*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>, author of this man page.
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--
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REPORTING BUGS
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--------------
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Report bugs to <linux-trace-devel@vger.kernel.org>
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LICENSE
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-------
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libtraceevent is Free Software licensed under the GNU LGPL 2.1
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RESOURCES
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---------
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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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