POSIX_TRACE_GETNEXT_EVENT(3P)

PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
posix_trace_getnext_event, posix_trace_timedgetnext_event, posix_trace_trygetnext_event — retrieve a trace event (TRACING)

SYNOPSIS

#include <sys/types.h>
#include <trace.h>

int posix_trace_getnext_event(trace_id_t trid,
    struct posix_trace_event_info *restrict event,
    void *restrict data, size_t num_bytes,
    size_t *restrict data_len, int *restrict unavailable);
int posix_trace_timedgetnext_event(trace_id_t trid,
    struct posix_trace_event_info *restrict event,
    void *restrict data, size_t num_bytes,
    size_t *restrict data_len, int *restrict unavailable,
    const struct timespec *restrict abstime);
int posix_trace_trygetnext_event(trace_id_t trid,
    struct posix_trace_event_info *restrict event,
    void *restrict data, size_t num_bytes,
    size_t *restrict data_len, int *restrict unavailable);

DESCRIPTION
The posix_trace_getnext_event() function shall report a recorded trace event either from an active trace stream without log or a pre-recorded trace stream identified by the trid argument. The posix_trace_trygetnext_event() function shall report a recorded trace event from an active trace stream without log identified by the trid argument.

The trace event information associated with the recorded trace event shall be copied by the function into the structure pointed to by the argument event and the data associated with the trace event shall be copied into the buffer pointed to by the data argument.

The posix_trace_getnext_event() function shall block if the trid argument identifies an active trace stream and there is currently no trace event ready to be retrieved. When returning, if a recorded trace event was reported, the variable pointed to by the unavailable argument shall be set to zero. Otherwise, the variable pointed to by the unavailable argument shall be set to a value different from zero.

The posix_trace_timedgetnext_event() function shall attempt to get another trace event from an active trace stream without log, as in the posix_trace_getnext_event() function. However, if no trace event is available from the trace stream, the implied wait shall be terminated when the timeout specified by the argument abstime expires, and the function shall return the error [ETIMEDOUT].

The timeout shall expire when the absolute time specified by abstime passes, as measured by the clock upon which timeouts are based (that is, when the value of that clock equals or exceeds abstime), or if the absolute time specified by abstime has already passed at the time of the call.

The timeout shall be based on the CLOCK_REALTIME clock. The resolution of the timeout shall be the resolution of the clock on which it is based. The timespec data type is defined in the <time.h> header.

Under no circumstance shall the function fail with a timeout if a trace event is immediately available from the trace stream. The validity of the abstime argument need not be checked if a trace event is immediately available from the trace stream.

The behavior of this function for a pre-recorded trace stream is unspecified.

The posix_trace_trygetnext_event() function shall not block. This function shall return an error if the trid argument identifies a pre-recorded trace stream. If a recorded trace event was reported, the variable pointed to by the unavailable argument shall be set to zero. Otherwise, if no trace event was reported, the variable pointed to by the unavailable argument shall be set to a value different from zero.

The argument num_bytes shall be the size of the buffer pointed to by the data argument. The argument data_len reports to the application the length in bytes of the data record just transferred. If num_bytes is greater than or equal to the size of the data associated with the trace event pointed to by the event argument, all the recorded data shall be transferred. In this case, the truncation-status member of the trace event structure shall be either POSIX_TRACE_NOT_TRUNCATED, if the trace event data was recorded without truncation while tracing, or POSIX_TRACE_TRUNCATED_RECORD, if the trace event data was truncated when it was recorded. If the num_bytes argument is less than the length of recorded trace event data, the data transferred shall be truncated to a length of num_bytes, the value stored in the variable pointed to by data_len shall be equal to num_bytes, and the truncation-status member of the event structure argument shall be set to POSIX_TRACE_TRUNCATED_READ (see the posix_trace_event_info structure defined in <trace.h>).

The report of a trace event shall be sequential starting from the oldest recorded trace event. Trace events shall be reported in the order in which they were generated, up to an implementation-defined time resolution that causes the ordering of trace events occurring very close to each other to be unknown. Once reported, a trace event cannot be reported again from an active trace stream. Once a trace event is reported from an active trace stream without log, the trace stream shall make the resources associated with that trace event available to record future generated trace events.

RETURN VALUE
Upon successful completion, these functions shall return a value of zero. Otherwise, they shall return the corresponding error number.

If successful, these functions store:

*   The recorded trace event in the object pointed to by event

*   The trace event information associated with the recorded trace event in the object pointed to by data

*   The length of this trace event information in the object pointed to by data_len

*   The value of zero in the object pointed to by unavailable

ERRORS
These functions shall fail if:

EINVAL
    The trace stream identifier argument trid is invalid.

The posix_trace_getnext_event() and posix_trace_timedgetnext_event() functions shall fail if:

EINTR
    The operation was interrupted by a signal, and so the call had no effect.

The posix_trace_trygetnext_event() function shall fail if:

EINVAL
    The trace stream identifier argument trid does not correspond to an active trace stream.

The posix_trace_timedgetnext_event() function shall fail if:

EINVAL
    There is no trace event immediately available from the trace stream, and the timeout argument is invalid.

ETIMEDOUT
    No trace event was available from the trace stream before the specified timeout timeout expired.

The following sections are informative.

EXAMPLES
None.

APPLICATION USAGE
None.

RATIONALE
None.

FUTURE DIRECTIONS
These functions may be removed in a future version.

SEE ALSO
posix_trace_close(), posix_trace_create()

The Base Definitions volume of POSIX.1-2017, <sys_types.h>, <trace.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .