trace_seq_init - Man Page

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
    mailto:rostedt@goodmis.org
  2. tz.stoyanov@gmail.com
    mailto:tz.stoyanov@gmail.com
  3. linux-trace-devel@vger.kernel.org
    mailto:linux-trace-devel@vger.kernel.org

Referenced By

The man pages trace_seq_destroy(3), trace_seq_do_fprintf(3), trace_seq_do_printf(3), trace_seq_printf(3), trace_seq_putc(3), trace_seq_puts(3), trace_seq_reset(3), trace_seq_terminate(3) and trace_seq_vprintf(3) are aliases of trace_seq_init(3).

02/08/2021 libtraceevent 1.1.1 libtraceevent Manual