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trace: emit name <-> ID mapping in simpletrace header
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Currently simpletrace assumes that events are given IDs
starting from 0, based on the order in which they appear
in the trace-events file, with no gaps. When the
trace-events file is split up, this assumption becomes
problematic.

To deal with this, extend the simpletrace format so that
it outputs a table of event name <-> ID mappings. That
will allow QEMU to assign arbitrary IDs to events without
breaking simpletrace parsing.

The v3 simple trace format was

  FILE HEADER
  EVENT TRACE RECORD 0
  EVENT TRACE RECORD 1
  ...
  EVENT TRACE RECORD N

The v4 simple trace format is now

  FILE HEADER
  EVENT MAPPING RECORD 0
  EVENT MAPPING RECORD 1
  ...
  EVENT MAPPING RECORD M
  EVENT TRACE RECORD RECORD 0
  EVENT TRACE RECORD RECORD 1
  ...
  EVENT TRACE RECORD N

Although this shows all the mapping records being emitted
upfront, this is not required by the format. While the main
simpletrace backend will emit all mappings at startup,
the systemtap simpletrace.stp script will emit the mappings
at first use. eg

  FILE HEADER
  ...
  EVENT MAPPING RECORD 0
  EVENT TRACE RECORD RECORD 0
  EVENT TRACE RECORD RECORD 1
  EVENT MAPPING RECORD 1
  EVENT TRACE RECORD RECORD 2
  ...
  EVENT TRACE RECORD N

This is more space efficient given that most trace records
only include a subset of events.

In modifying the systemtap simpletrace code, a 'begin' probe
was added to emit the trace event header, so you no longer
need to add '--no-header' when running simpletrace.py for
systemtap generated trace files.

Signed-off-by: Daniel P. Berrange <[email protected]>
Message-id: [email protected]
Signed-off-by: Stefan Hajnoczi <[email protected]>
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@berrange @stefanhaRH
berrange authored and stefanhaRH committed Oct 12, 2016
1 parent ef4c9fc commit 7f1b588
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Showing 3 changed files with 89 additions and 18 deletions.
50 changes: 36 additions & 14 deletions scripts/simpletrace.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,9 @@
header_magic = 0xf2b177cb0aa429b4
dropped_event_id = 0xfffffffffffffffe

record_type_mapping = 0
record_type_event = 1

log_header_fmt = '=QQQ'
rec_header_fmt = '=QQII'

Expand All @@ -30,14 +33,16 @@ def read_header(fobj, hfmt):
return None
return struct.unpack(hfmt, hdr)

def get_record(edict, rechdr, fobj):
"""Deserialize a trace record from a file into a tuple (event_num, timestamp, pid, arg1, ..., arg6)."""
def get_record(edict, idtoname, rechdr, fobj):
"""Deserialize a trace record from a file into a tuple
(name, timestamp, pid, arg1, ..., arg6)."""
if rechdr is None:
return None
rec = (rechdr[0], rechdr[1], rechdr[3])
if rechdr[0] != dropped_event_id:
event_id = rechdr[0]
event = edict[event_id]
name = idtoname[event_id]
rec = (name, rechdr[1], rechdr[3])
event = edict[name]
for type, name in event.args:
if is_string(type):
l = fobj.read(4)
Expand All @@ -48,15 +53,22 @@ def get_record(edict, rechdr, fobj):
(value,) = struct.unpack('=Q', fobj.read(8))
rec = rec + (value,)
else:
rec = ("dropped", rechdr[1], rechdr[3])
(value,) = struct.unpack('=Q', fobj.read(8))
rec = rec + (value,)
return rec

def get_mapping(fobj):
(event_id, ) = struct.unpack('=Q', fobj.read(8))
(len, ) = struct.unpack('=L', fobj.read(4))
name = fobj.read(len)

return (event_id, name)

def read_record(edict, fobj):
def read_record(edict, idtoname, fobj):
"""Deserialize a trace record from a file into a tuple (event_num, timestamp, pid, arg1, ..., arg6)."""
rechdr = read_header(fobj, rec_header_fmt)
return get_record(edict, rechdr, fobj) # return tuple of record elements
return get_record(edict, idtoname, rechdr, fobj)

def read_trace_header(fobj):
"""Read and verify trace file header"""
Expand All @@ -67,20 +79,30 @@ def read_trace_header(fobj):
raise ValueError('Not a valid trace file!')

log_version = header[2]
if log_version not in [0, 2, 3]:
if log_version not in [0, 2, 3, 4]:
raise ValueError('Unknown version of tracelog format!')
if log_version != 3:
if log_version != 4:
raise ValueError('Log format %d not supported with this QEMU release!'
% log_version)

def read_trace_records(edict, fobj):
"""Deserialize trace records from a file, yielding record tuples (event_num, timestamp, pid, arg1, ..., arg6)."""
idtoname = {
dropped_event_id: "dropped"
}
while True:
rec = read_record(edict, fobj)
if rec is None:
t = fobj.read(8)
if len(t) == 0:
break

yield rec
(rectype, ) = struct.unpack('=Q', t)
if rectype == record_type_mapping:
event_id, name = get_mapping(fobj)
idtoname[event_id] = name
else:
rec = read_record(edict, idtoname, fobj)

yield rec

class Analyzer(object):
"""A trace file analyzer which processes trace records.
Expand Down Expand Up @@ -115,10 +137,10 @@ def process(events, log, analyzer, read_header=True):
read_trace_header(log)

dropped_event = Event.build("Dropped_Event(uint64_t num_events_dropped)")
edict = {dropped_event_id: dropped_event}
edict = {"dropped": dropped_event}

for num, event in enumerate(events):
edict[num] = event
for event in events:
edict[event.name] = event

def build_fn(analyzer, event):
if isinstance(event, str):
Expand Down
24 changes: 22 additions & 2 deletions scripts/tracetool/format/simpletrace_stap.py
View file
Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,25 @@

def generate(events, backend):
out('/* This file is autogenerated by tracetool, do not edit. */',
'',
'global event_name_to_id_map',
'global event_next_id',
'function simple_trace_map_event(name)',
'',
'{',
' if (!([name] in event_name_to_id_map)) {',
' event_name_to_id_map[name] = event_next_id',
' name_len = strlen(name)',
' printf("%%8b%%8b%%4b%%.*s", 0, ',
' event_next_id, name_len, name_len, name)',
' event_next_id = event_next_id + 1',
' }',
' return event_name_to_id_map[name]',
'}',
'probe begin',
'{',
' printf("%%8b%%8b%%8b", 0xffffffffffffffff, 0xf2b177cb0aa429b4, 4)',
'}',
'')

for event_id, e in enumerate(events):
Expand All @@ -29,6 +48,7 @@ def generate(events, backend):

out('probe %(probeprefix)s.simpletrace.%(name)s = %(probeprefix)s.%(name)s ?',
'{',
' id = simple_trace_map_event("%(name)s")',
probeprefix=probeprefix(),
name=e.name)

Expand All @@ -48,7 +68,7 @@ def generate(events, backend):
sizestr = ' + '.join(sizes)

# Generate format string and value pairs for record header and arguments
fields = [('8b', str(event_id)),
fields = [('8b', 'id'),
('8b', 'gettimeofday_ns()'),
('4b', sizestr),
('4b', 'pid()')]
Expand All @@ -63,7 +83,7 @@ def generate(events, backend):
# Emit the entire record in a single SystemTap printf()
fmt_str = '%'.join(fmt for fmt, _ in fields)
arg_str = ', '.join(arg for _, arg in fields)
out(' printf("%%%(fmt_str)s", %(arg_str)s)',
out(' printf("%%8b%%%(fmt_str)s", 1, %(arg_str)s)',
fmt_str=fmt_str, arg_str=arg_str)

out('}')
Expand Down
33 changes: 31 additions & 2 deletions trace/simple.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,7 +24,7 @@
#define HEADER_MAGIC 0xf2b177cb0aa429b4ULL

/** Trace file version number, bump if format changes */
#define HEADER_VERSION 3
#define HEADER_VERSION 4

/** Records were dropped event ID */
#define DROPPED_EVENT_ID (~(uint64_t)0 - 1)
Expand Down Expand Up @@ -56,6 +56,9 @@ static uint32_t trace_pid;
static FILE *trace_fp;
static char *trace_file_name;

#define TRACE_RECORD_TYPE_MAPPING 0
#define TRACE_RECORD_TYPE_EVENT 1

/* * Trace buffer entry */
typedef struct {
uint64_t event; /* event ID value */
Expand Down Expand Up @@ -160,6 +163,7 @@ static gpointer writeout_thread(gpointer opaque)
unsigned int idx = 0;
int dropped_count;
size_t unused __attribute__ ((unused));
uint64_t type = TRACE_RECORD_TYPE_EVENT;

for (;;) {
wait_for_trace_records_available();
Expand All @@ -174,10 +178,12 @@ static gpointer writeout_thread(gpointer opaque)
} while (!g_atomic_int_compare_and_exchange(&dropped_events,
dropped_count, 0));
dropped.rec.arguments[0] = dropped_count;
unused = fwrite(&type, sizeof(type), 1, trace_fp);
unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
}

while (get_trace_record(idx, &recordptr)) {
unused = fwrite(&type, sizeof(type), 1, trace_fp);
unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
writeout_idx += recordptr->length;
free(recordptr); /* don't use g_free, can deadlock when traced */
Expand Down Expand Up @@ -273,6 +279,28 @@ void trace_record_finish(TraceBufferRecord *rec)
}
}

static int st_write_event_mapping(void)
{
uint64_t type = TRACE_RECORD_TYPE_MAPPING;
TraceEventIter iter;
TraceEvent *ev;

trace_event_iter_init(&iter, NULL);
while ((ev = trace_event_iter_next(&iter)) != NULL) {
uint64_t id = trace_event_get_id(ev);
const char *name = trace_event_get_name(ev);
uint32_t len = strlen(name);
if (fwrite(&type, sizeof(type), 1, trace_fp) != 1 ||
fwrite(&id, sizeof(id), 1, trace_fp) != 1 ||
fwrite(&len, sizeof(len), 1, trace_fp) != 1 ||
fwrite(name, len, 1, trace_fp) != 1) {
return -1;
}
}

return 0;
}

void st_set_trace_file_enabled(bool enable)
{
if (enable == !!trace_fp) {
Expand All @@ -297,7 +325,8 @@ void st_set_trace_file_enabled(bool enable)
return;
}

if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {
if (fwrite(&header, sizeof header, 1, trace_fp) != 1 ||
st_write_event_mapping() < 0) {
fclose(trace_fp);
trace_fp = NULL;
return;
Expand Down

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