On Wed, 1 Jul 2026 08:45:40 +0200
Tomas Glozar [off-list ref] wrote:

I double-checked that and you are correct that the docstring says so,
but it's an error in the docstring. According to the manpage, it
returns the number of bytes written (i.e. positive on success, not
zero) [1]:

Note, the man page is considered the source of "truth".

"RETURN VALUE
...
tracefs_event_file_write() and tracefs_event_file_append() returns
*the number of bytes written to the system/event file* or negative on
error."

The code agrees as well: in tracefs_event_file_write() there's the
wrong docstring (likely copied from another function) [2]:

/*
 * tracefs_event_file_write - write to an event file
 * ...
 * Return 0 on success, and -1 on error.

Ug, that's a bug and needs to be fixed.

Thanks for catching this. I need to spend some time to catch up on the user
side of tracing. There's a few new bugzillas and patches I need to apply.

-- Steve

 */
int tracefs_event_file_write(struct tracefs_instance *instance,
    const char *system, const char *event,
    const char *file, const char *str)
{
        ....
        ret = tracefs_instance_file_write(instance, path, str);
        free(path);
        return ret;
}