freebsd-dev/lib/libpmc/pmclog.3

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.Dd June 1, 2005
.Os
.Dt PMCLOG 3
.Sh NAME
.Nm pmclog_open ,
.Nm pmclog_close ,
.Nm pmclog_read ,
.Nm pmclog_feed
.Nd parse event log data generated by
.Xr hwpmc 4
.Sh LIBRARY
.Lb libpmc
.Sh SYNOPSIS
.In pmclog.h
.Ft "void *"
.Fn pmclog_open "int fd"
.Ft void
.Fn pmclog_close "void *cookie"
.Ft int
.Fn pmclog_read "void *cookie" "struct pmclog_ev *ev"
.Ft int
.Fn pmclog_feed "void *cookie" "char *data" "int len"
.Sh DESCRIPTION
These functions provide a way for application programs to extract
events from an event stream generated by
.Xr hwpmc 4 .
.Pp
A new event log parser is allocated using
.Fn pmclog_open .
Argument
.Fa fd
may be a file descriptor opened for reading if the event stream is
present in a file, or the constant
.Dv 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.
.Pp
Function
.Fn pmclog_read
returns the next available event in the event stream associated with
argument
.Fa cookie .
Argument
.Fa ev
points to an event descriptor that which will contain the result of a
successfully parsed event.
.Pp
An event descriptor returned by
.Fn pmclog_read
has the following structure:
.Bd -literal
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_allocate   pl_a;
		struct pmclog_ev_proccsw    pl_c;
		struct pmclog_ev_dropnotify pl_d;
		struct pmclog_ev_procexit   pl_e;
		struct pmclog_ev_initialize pl_i;
		struct pmclog_ev_pcsample   pl_s;
		struct pmclog_ev_pmcattach  pl_t;
		struct pmclog_ev_userdata   pl_u;
		struct pmclog_ev_procexec   pl_x;
       } pl_u;
};
.Ed
.Pp
The current state of the parser is recorded in
.Va pl_state .
This field can take on the following values:
.Bl -tag -width ".Dv PMCLOG_REQUIRE_DATA"
.It Dv PMCLOG_EOF
(For file based parsers only)
An end-of-file condition was encountered on the configured file
descriptor.
.It Dv PMCLOG_ERROR
An error occurred during parsing.
.It Dv PMCLOG_OK
A complete event record was read into
.Fa *ev .
.It Dv 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
.Fn pmclog_feed .
For file based parsers, function
.Fn pmclog_read
may be retried when data is available on the configured file
descriptor.
.El
.Pp
The rest of the event structure is valid only if field
.Va pl_state
contains
.Dv PMCLOG_OK .
Field
.Va pl_offset
contains the offset of the current record in the byte stream.
Field
.Va pl_count
contains the serial number of this event.
Field
.Va pl_ts
contains a timestamp with the system time when the event occurred.
Field
.Va pl_type
denotes the kind of the event returned in argument
.Fa *ev
and is one of the following:
.Bl -tag -width ".Dv PMCLOG_TYPE_PMCALLOCATE"
.It Dv PMCLOG_TYPE_DROPNOTIFY
a marker indicating that
.Xr hwpmc 4
had to drop data due to a resource constraint.
.It Dv PMCLOG_TYPE_INITIALIZE
an initialization record.
This is usually the first record in a log file.
.It Dv PMCLOG_TYPE_PCSAMPLE
A record containing an instruction pointer sample.
.It Dv PMCLOG_TYPE_PMCALLOCATE
A record describing a PMC allocation operation.
.It Dv PMCLOG_TYPE_PMCATTACH
A record describing a PMC attach operation.
.It Dv PMCLOG_TYPE_PROCCSW
A record describing a PMC reading at the time of a process context switch.
.It Dv PMCLOG_TYPE_PROCEXIT
A record describing the accumulated PMC reading for a process at the
time of
.Xr _exit 2 .
.It Dv PMCLOG_TYPE_PROCEXEC
A record describing an
.Xr execve 2
by a target process.
.It Dv PMCLOG_TYPE_USERDATA
A record containing user data.
.El
.Pp
Function
.Fn pmclog_feed
is used with parsers configured to parse memory based event streams.
It is intended to be called when function
.Fn pmclog_read
indicates the need for more data by a returning
.Dv PMCLOG_REQUIRE_DATA
in field
.Va pl_state
of its event structure argument.
Argument
.Fa data
points to the start of a memory buffer containing fresh event data.
Argument
.Fa len
indicates the number of data bytes available.
The memory range
.Bq Fa data , Fa data No + Fa len
must remain valid till the next time
.Fn pmclog_read
returns an error.
It is an error to use
.Fn pmclog_feed
on a parser configured to parse file data.
.Pp
Function
.Fn pmclog_close
releases the internal state allocated by a prior call
to
.Fn pmclog_open .
.Sh RETURN VALUES
Function
.Fn pmclog_open
will return a
.No non- Ns Dv NULL
value if successful or
.Dv NULL
otherwise.
.Pp
Function
.Fn pmclog_read
will return 0 in case a complete event record was successfully read,
or will return \-1 and will set the
.Va pl_state
field of the event record to the appropriate code in case of an error.
.Pp
Function
.Fn pmclog_feed
will return 0 on success or \-1 in case of failure.
.Sh EXAMPLES
A template for using the log file parsing API is shown below in pseudocode:
.Bd -literal
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 */
.Ed
.Sh ERRORS
A call to
.Fn pmclog_init_parser
may fail with any of the errors returned by
.Xr malloc 3 .
.Pp
A call to
.Fn pmclog_read
for a file based parser may fail with any of the errors returned by
.Xr read 2 .
.Sh SEE ALSO
.Xr read 2 ,
.Xr malloc 3 ,
.Xr pmc 3 ,
.Xr hwpmc 4 ,
.Xr pmcstat 8