xref: /aosp_15_r20/external/libtraceevent/Documentation/libtraceevent-tseq.txt (revision 436bf2bcd5202612ffffe471bbcc1f277cc8d28e)

libtraceevent(3)
================

NAME
----
trace_seq_init, trace_seq_destroy, trace_seq_reset, trace_seq_terminate,
trace_seq_putc, trace_seq_puts, trace_seq_printf, trace_seq_vprintf,
trace_seq_do_fprintf, trace_seq_do_printf -
Initialize / destroy a trace sequence.

SYNOPSIS
--------
[verse]
--
*#include <event-parse.h>*
*#include <trace-seq.h>*

void *trace_seq_init*(struct trace_seq pass:[*]_s_);
void *trace_seq_destroy*(struct trace_seq pass:[*]_s_);
void *trace_seq_reset*(struct trace_seq pass:[*]_s_);
void *trace_seq_terminate*(struct trace_seq pass:[*]_s_);
int *trace_seq_putc*(struct trace_seq pass:[*]_s_, unsigned char _c_);
int *trace_seq_puts*(struct trace_seq pass:[*]_s_, const char pass:[*]_str_);
int *trace_seq_printf*(struct trace_seq pass:[*]_s_, const char pass:[*]_fmt_, _..._);
int *trace_seq_vprintf*(struct trace_seq pass:[*]_s_, const char pass:[*]_fmt_, va_list _args_);
int *trace_seq_do_printf*(struct trace_seq pass:[*]_s_);
int *trace_seq_do_fprintf*(struct trace_seq pass:[*]_s_, FILE pass:[*]_fp_);
--

DESCRIPTION
-----------
Trace sequences are used to allow a function to call several other functions
to create a string of data to use.

The *trace_seq_init()* function initializes the trace sequence _s_.

The *trace_seq_destroy()* function destroys the trace sequence _s_ and frees
all its resources that it had used.

The *trace_seq_reset()* function re-initializes the trace sequence _s_. All
characters already written in _s_ will be deleted.

The *trace_seq_terminate()* function terminates the trace sequence _s_. It puts
the null character pass:['\0'] at the end of the buffer.

The *trace_seq_putc()* function puts a single character _c_ in the trace
sequence _s_.

The *trace_seq_puts()* function puts a NULL terminated string _str_ in the
trace sequence _s_.

The *trace_seq_printf()* function puts a formated string _fmt _with
variable arguments _..._ in the trace sequence _s_.

The *trace_seq_vprintf()* function puts a formated string _fmt _with
list of arguments _args_ in the trace sequence _s_.

The *trace_seq_do_printf()* function prints the buffer of trace sequence _s_ to
the standard output stdout.

The *trace_seq_do_fprintf()* function prints the buffer of trace sequence _s_
to the given file _fp_.

RETURN VALUE
------------
Both *trace_seq_putc()* and *trace_seq_puts()* functions return the number of
characters put in the trace sequence, or 0 in case of an error

Both *trace_seq_printf()* and *trace_seq_vprintf()* functions return 0 if the
trace oversizes the buffer's free space, the number of characters printed, or
a negative value in case of an error.

Both *trace_seq_do_printf()* and *trace_seq_do_fprintf()* functions return the
number of printed characters, or -1 in case of an error.

EXAMPLE
-------
[source,c]
--
#include <event-parse.h>
#include <trace-seq.h>
...
struct trace_seq seq;
trace_seq_init(&seq);
...
void foo_seq_print(struct trace_seq *tseq, char *format, ...)
{
	va_list ap;
	va_start(ap, format);
	if (trace_seq_vprintf(tseq, format, ap) <= 0) {
		/* Failed to print in the trace sequence */
	}
	va_end(ap);
}

trace_seq_reset(&seq);

char *str = " MAN page example";
if (trace_seq_puts(&seq, str) != strlen(str)) {
	/* Failed to put str in the trace sequence */
}
if (trace_seq_putc(&seq, ':') != 1) {
	/* Failed to put ':' in the trace sequence */
}
if (trace_seq_printf(&seq, " trace sequence: %d", 1) <= 0) {
	/* Failed to print in the trace sequence */
}
foo_seq_print( &seq, "  %d\n", 2);

trace_seq_terminate(&seq);
...

if (trace_seq_do_printf(&seq) < 0 ) {
	/* Failed to print the sequence buffer to the standard output */
}
FILE *fp = fopen("trace.txt", "w");
if (trace_seq_do_fprintf(&seq, fp) < 0 ) [
	/* Failed to print the sequence buffer to the trace.txt file */
}

trace_seq_destroy(&seq);
...
--

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.
*-ltraceevent*
	Linker switch to add when building a program that uses the library.
--

SEE ALSO
--------
*libtraceevent*(3), *trace-cmd*(1)

AUTHOR
------
[verse]
--
*Steven Rostedt* <[email protected]>, author of *libtraceevent*.
*Tzvetomir Stoyanov* <[email protected]>, author of this man page.
--
REPORTING BUGS
--------------
Report bugs to  <[email protected]>

LICENSE
-------
libtraceevent is Free Software licensed under the GNU LGPL 2.1

RESOURCES
---------
https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/