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¶

#include <event-parse.h>
#include <trace-seq.h>
void trace_seq_init(struct trace_seq *s);
void trace_seq_destroy(struct trace_seq *s);
void trace_seq_reset(struct trace_seq *s);
void trace_seq_terminate(struct trace_seq *s);
int trace_seq_putc(struct trace_seq *s, unsigned char c);
int trace_seq_puts(struct trace_seq *s, const char *str);
int trace_seq_printf(struct trace_seq *s, const char *fmt, ...);
int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args);
int trace_seq_do_printf(struct trace_seq *s);
int trace_seq_do_fprintf(struct trace_seq *s, FILE *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 '\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¶

#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¶

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¶

Steven Rostedt <rostedt@goodmis.org[1]>, author of libtraceevent.
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>, author of this man page.

REPORTING BUGS¶

Report bugs to <linux-trace-devel@vger.kernel.org[3]>

LICENSE¶

libtraceevent is Free Software licensed under the GNU LGPL 2.1

RESOURCES¶

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

NOTES¶

1.

rostedt@goodmis.org

2.

tz.stoyanov@gmail.com

3.

linux-trace-devel@vger.kernel.org