NAME
pmclog_open, pmclog_close, pmclog_read, pmclog_feed – parse event log data generated by hwpmc(4)
LIBRARY
library “libpmc”
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 structure:
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 */
union {
uint64_t pl_tsc; /* TSC timestamp */
struct timespec pl_ts; /* log entry timestamp (legacy) */
};
enum pmclog_type pl_type; /* log entry kind */
union { /* log entry data */
struct pmclog_ev_callchain pl_cc;
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_pmcallocate pl_a;
struct pmclog_ev_pmcallocatedyn pl_ad;
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 condition was encountered on the configured file descriptor.
- 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_tsc carries the raw CPU Time Stamp Counter (TSC) value recorded at the time of the event. This is not a wall-clock time; to convert to nanoseconds divide the TSC delta between two events by the TSC frequency (pl_u.pl_i.pl_tsc_freq) reported in the PMCLOG_TYPE_INITIALIZE record. The legacy pl_ts member aliases the same storage for ABI compatibility, but its contents no longer represent a wall-clock timestamp.
Note that TSC-based timestamps and pl_u.pl_i.pl_tsc_freq are only meaningful on x86 architectures (amd64 and i386). On all other architectures (including arm64 and powerpc), pl_tsc and pl_u.pl_i.pl_tsc_freq are set to zero. 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 mapping 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 sample.
- 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 processes 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 pseudocode:
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_CALLCHAIN:
--process a callchain 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
HISTORY
The pmclog API first appeared in FreeBSD 6.0.