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

CONTENTS

Library
Synopsis
Description
Return Values
Examples
Errors
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.Lb libpmc

.In 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

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 */
       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;
};

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_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_MAPPINGCHANGE
	A record describing an address space change for a process.
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.

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.

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_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 */

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).

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

The pmclog(3) API
.Ud It first appeared in
.Fx 6.0 .

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