pmclog_read man page on FreeBSD

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PMCLOG(3)		 BSD Library Functions Manual		     PMCLOG(3)

NAME
     pmclog_open, pmclog_close, pmclog_read, pmclog_feed — parse event log
     data generated by hwpmc(4)

LIBRARY
     Performance Counters Library (libpmc, -lpmc)

SYNOPSIS
     #include <pmclog.h>

     void *
     pmclog_open(int fd);

     void
     pmclog_close(void *cookie);

     int
     pmclog_read(void *cookie, struct pmclog_ev *ev);

     int
     pmclog_feed(void *cookie, char *data, int len);

DESCRIPTION
     These functions provide a way for application programs to extract events
     from an event stream generated by hwpmc(4).

     A new event log parser is allocated using pmclog_open().  Argument fd may
     be a file descriptor opened for reading if the event stream is present in
     a file, or the constant PMCLOG_FD_NONE for an event stream present in
     memory.  This function returns a cookie that is passed into the other
     functions in this API set.

     Function pmclog_read() returns the next available event in the event
     stream associated with argument cookie.  Argument ev points to an event
     descriptor that which will contain the result of a successfully parsed
     event.

     An event descriptor returned by pmclog_read() has the following struc‐
     ture:

     struct pmclog_ev {
	    enum pmclog_state pl_state;	     /* parser state after 'get_event()' */
	    off_t	      pl_offset;     /* byte offset in stream */
	    size_t	      pl_count;	     /* count of records so far */
	    struct timespec   pl_ts;	     /* log entry timestamp */
	    enum pmclog_type  pl_type;	     /* log entry kind */
	    union {			     /* log entry data */
		     struct pmclog_ev_closelog	  pl_cl;
		     struct pmclog_ev_dropnotify  pl_d;
		     struct pmclog_ev_initialize  pl_i;
		     struct pmclog_ev_map_in	  pl_mi;
		     struct pmclog_ev_map_out	  pl_mo;
		     struct pmclog_ev_pcsample	  pl_s;
		     struct pmclog_ev_pmcallocate pl_a;
		     struct pmclog_ev_pmcattach	  pl_t;
		     struct pmclog_ev_pmcdetach	  pl_d;
		     struct pmclog_ev_proccsw	  pl_c;
		     struct pmclog_ev_procexec	  pl_x;
		     struct pmclog_ev_procexit	  pl_e;
		     struct pmclog_ev_procfork	  pl_f;
		     struct pmclog_ev_sysexit	  pl_e;
		     struct pmclog_ev_userdata	  pl_u;
	    } pl_u;
     };

     The current state of the parser is recorded in pl_state.  This field can
     take on the following values:

     PMCLOG_EOF		  (For file based parsers only) An end-of-file condi‐
			  tion was encountered on the configured file descrip‐
			  tor.

     PMCLOG_ERROR	  An error occurred during parsing.

     PMCLOG_OK		  A complete event record was read into *ev.

     PMCLOG_REQUIRE_DATA  There was insufficient data in the event stream to
			  assemble a complete event record.  For memory based
			  parsers, more data can be fed to the parser using
			  function pmclog_feed().  For file based parsers,
			  function pmclog_read() may be retried when data is
			  available on the configured file descriptor.

     The rest of the event structure is valid only if field pl_state contains
     PMCLOG_OK.	 Field pl_offset contains the offset of the current record in
     the byte stream.  Field pl_count contains the serial number of this
     event.  Field pl_ts contains a timestamp with the system time when the
     event occurred.  Field pl_type denotes the kind of the event returned in
     argument *ev and is one of the following:

     PMCLOG_TYPE_CLOSELOG     A marker indicating a successful close of a log
			      file.  This record will be the last record of a
			      log file.

     PMCLOG_TYPE_DROPNOTIFY   A marker indicating that hwpmc(4) had to drop
			      data due to a resource constraint.

     PMCLOG_TYPE_INITIALIZE   An initialization record.	 This is the first
			      record in a log file.

     PMCLOG_TYPE_MAP_IN	      A record describing the introduction of a map‐
			      ping to an executable object by a kldload(2) or
			      mmap(2) system call.

     PMCLOG_TYPE_MAP_OUT      A record describing the removal of a mapping to
			      an executable object by a kldunload(2) or
			      munmap(2) system call.

     PMCLOG_TYPE_PCSAMPLE     A record containing an instruction pointer sam‐
			      ple.

     PMCLOG_TYPE_PMCALLOCATE  A record describing a PMC allocation operation.

     PMCLOG_TYPE_PMCATTACH    A record describing a PMC attach operation.

     PMCLOG_TYPE_PMCDETACH    A record describing a PMC detach operation.

     PMCLOG_TYPE_PROCCSW      A record describing a PMC reading at the time of
			      a process context switch.

     PMCLOG_TYPE_PROCEXEC     A record describing an execve(2) by a target
			      process.

     PMCLOG_TYPE_PROCEXIT     A record describing the accumulated PMC reading
			      for a process at the time of _exit(2).

     PMCLOG_TYPE_PROCFORK     A record describing a fork(2) by a target
			      process.

     PMCLOG_TYPE_SYSEXIT      A record describing a process exit, sent to pro‐
			      cesses owning system-wide sampling PMCs.

     PMCLOG_TYPE_USERDATA     A record containing user data.

     Function pmclog_feed() is used with parsers configured to parse memory
     based event streams.  It is intended to be called when function
     pmclog_read() indicates the need for more data by a returning
     PMCLOG_REQUIRE_DATA in field pl_state of its event structure argument.
     Argument data points to the start of a memory buffer containing fresh
     event data.  Argument len indicates the number of data bytes available.
     The memory range [data, data + len] must remain valid till the next time
     pmclog_read() returns an error.  It is an error to use pmclog_feed() on a
     parser configured to parse file data.

     Function pmclog_close() releases the internal state allocated by a prior
     call to pmclog_open().

RETURN VALUES
     Function pmclog_open() will return a non-NULL value if successful or NULL
     otherwise.

     Function pmclog_read() will return 0 in case a complete event record was
     successfully read, or will return -1 and will set the pl_state field of
     the event record to the appropriate code in case of an error.

     Function pmclog_feed() will return 0 on success or -1 in case of failure.

EXAMPLES
     A template for using the log file parsing API is shown below in pseu‐
     docode:

     void *parser;		     /* cookie */
     struct pmclog_ev ev;	     /* parsed event */
     int fd;			     /* file descriptor */

     fd = open(filename, O_RDONLY);  /* open log file */
     parser = pmclog_open(fd);	     /* initialize parser */
     if (parser == NULL)
	     --handle an out of memory error--;

     /* read and parse data */
     while (pmclog_read(parser, &ev) == 0) {
	     assert(ev.pl_state == PMCLOG_OK);
	     /* process the event */
	     switch (ev.pl_type) {
	     case PMCLOG_TYPE_ALLOCATE:
		     --process a pmc allocation record--
		     break;
	     case PMCLOG_TYPE_PROCCSW:
		     --process a thread context switch record--
		     break;
	     case PMCLOG_TYPE_PCSAMPLE:
		     --process a PC sample--
		     break;
	     --and so on--
	     }
     }

     /* examine parser state */
     switch (ev.pl_state) {
     case PMCLOG_EOF:
	     --normal termination--
	     break;
     case PMCLOG_ERROR:
	     --look at errno here--
	     break;
     case PMCLOG_REQUIRE_DATA:
	     --arrange for more data to be available for parsing--
	     break;
     default:
	     assert(0);
	     /*NOTREACHED*/
     }

     pmclog_close(parser);	     /* cleanup */

ERRORS
     A call to pmclog_init_parser() may fail with any of the errors returned
     by malloc(3).

     A call to pmclog_read() for a file based parser may fail with any of the
     errors returned by read(2).

SEE ALSO
     read(2), malloc(3), pmc(3), hwpmc(4), pmcstat(8)

HISTORY
     The pmclog API currently under development.  It first appeared in
     FreeBSD 6.0.

BSD				March 26, 2006				   BSD
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