quorum: Avoid bdrv_aio_writev() for rewrites
[qemu.git] / trace / simple.c
1 /*
2 * Simple trace backend
3 *
4 * Copyright IBM, Corp. 2010
5 *
6 * This work is licensed under the terms of the GNU GPL, version 2. See
7 * the COPYING file in the top-level directory.
8 *
9 */
10
11 #include "qemu/osdep.h"
12 #ifndef _WIN32
13 #include <pthread.h>
14 #endif
15 #include "qemu/timer.h"
16 #include "trace.h"
17 #include "trace/control.h"
18 #include "trace/simple.h"
19
20 /** Trace file header event ID, picked to avoid conflict with real event IDs */
21 #define HEADER_EVENT_ID (~(uint64_t)0)
22
23 /** Trace file magic number */
24 #define HEADER_MAGIC 0xf2b177cb0aa429b4ULL
25
26 /** Trace file version number, bump if format changes */
27 #define HEADER_VERSION 4
28
29 /** Records were dropped event ID */
30 #define DROPPED_EVENT_ID (~(uint64_t)0 - 1)
31
32 /** Trace record is valid */
33 #define TRACE_RECORD_VALID ((uint64_t)1 << 63)
34
35 /*
36 * Trace records are written out by a dedicated thread. The thread waits for
37 * records to become available, writes them out, and then waits again.
38 */
39 static CompatGMutex trace_lock;
40 static CompatGCond trace_available_cond;
41 static CompatGCond trace_empty_cond;
42
43 static bool trace_available;
44 static bool trace_writeout_enabled;
45
46 enum {
47 TRACE_BUF_LEN = 4096 * 64,
48 TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
49 };
50
51 uint8_t trace_buf[TRACE_BUF_LEN];
52 static volatile gint trace_idx;
53 static unsigned int writeout_idx;
54 static volatile gint dropped_events;
55 static uint32_t trace_pid;
56 static FILE *trace_fp;
57 static char *trace_file_name;
58
59 #define TRACE_RECORD_TYPE_MAPPING 0
60 #define TRACE_RECORD_TYPE_EVENT 1
61
62 /* * Trace buffer entry */
63 typedef struct {
64 uint64_t event; /* event ID value */
65 uint64_t timestamp_ns;
66 uint32_t length; /* in bytes */
67 uint32_t pid;
68 uint64_t arguments[];
69 } TraceRecord;
70
71 typedef struct {
72 uint64_t header_event_id; /* HEADER_EVENT_ID */
73 uint64_t header_magic; /* HEADER_MAGIC */
74 uint64_t header_version; /* HEADER_VERSION */
75 } TraceLogHeader;
76
77
78 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
79 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
80
81 static void clear_buffer_range(unsigned int idx, size_t len)
82 {
83 uint32_t num = 0;
84 while (num < len) {
85 if (idx >= TRACE_BUF_LEN) {
86 idx = idx % TRACE_BUF_LEN;
87 }
88 trace_buf[idx++] = 0;
89 num++;
90 }
91 }
92 /**
93 * Read a trace record from the trace buffer
94 *
95 * @idx Trace buffer index
96 * @record Trace record to fill
97 *
98 * Returns false if the record is not valid.
99 */
100 static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)
101 {
102 uint64_t event_flag = 0;
103 TraceRecord record;
104 /* read the event flag to see if its a valid record */
105 read_from_buffer(idx, &record, sizeof(event_flag));
106
107 if (!(record.event & TRACE_RECORD_VALID)) {
108 return false;
109 }
110
111 smp_rmb(); /* read memory barrier before accessing record */
112 /* read the record header to know record length */
113 read_from_buffer(idx, &record, sizeof(TraceRecord));
114 *recordptr = malloc(record.length); /* don't use g_malloc, can deadlock when traced */
115 /* make a copy of record to avoid being overwritten */
116 read_from_buffer(idx, *recordptr, record.length);
117 smp_rmb(); /* memory barrier before clearing valid flag */
118 (*recordptr)->event &= ~TRACE_RECORD_VALID;
119 /* clear the trace buffer range for consumed record otherwise any byte
120 * with its MSB set may be considered as a valid event id when the writer
121 * thread crosses this range of buffer again.
122 */
123 clear_buffer_range(idx, record.length);
124 return true;
125 }
126
127 /**
128 * Kick writeout thread
129 *
130 * @wait Whether to wait for writeout thread to complete
131 */
132 static void flush_trace_file(bool wait)
133 {
134 g_mutex_lock(&trace_lock);
135 trace_available = true;
136 g_cond_signal(&trace_available_cond);
137
138 if (wait) {
139 g_cond_wait(&trace_empty_cond, &trace_lock);
140 }
141
142 g_mutex_unlock(&trace_lock);
143 }
144
145 static void wait_for_trace_records_available(void)
146 {
147 g_mutex_lock(&trace_lock);
148 while (!(trace_available && trace_writeout_enabled)) {
149 g_cond_signal(&trace_empty_cond);
150 g_cond_wait(&trace_available_cond, &trace_lock);
151 }
152 trace_available = false;
153 g_mutex_unlock(&trace_lock);
154 }
155
156 static gpointer writeout_thread(gpointer opaque)
157 {
158 TraceRecord *recordptr;
159 union {
160 TraceRecord rec;
161 uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];
162 } dropped;
163 unsigned int idx = 0;
164 int dropped_count;
165 size_t unused __attribute__ ((unused));
166 uint64_t type = TRACE_RECORD_TYPE_EVENT;
167
168 for (;;) {
169 wait_for_trace_records_available();
170
171 if (g_atomic_int_get(&dropped_events)) {
172 dropped.rec.event = DROPPED_EVENT_ID,
173 dropped.rec.timestamp_ns = get_clock();
174 dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
175 dropped.rec.pid = trace_pid;
176 do {
177 dropped_count = g_atomic_int_get(&dropped_events);
178 } while (!g_atomic_int_compare_and_exchange(&dropped_events,
179 dropped_count, 0));
180 dropped.rec.arguments[0] = dropped_count;
181 unused = fwrite(&type, sizeof(type), 1, trace_fp);
182 unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
183 }
184
185 while (get_trace_record(idx, &recordptr)) {
186 unused = fwrite(&type, sizeof(type), 1, trace_fp);
187 unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
188 writeout_idx += recordptr->length;
189 free(recordptr); /* don't use g_free, can deadlock when traced */
190 idx = writeout_idx % TRACE_BUF_LEN;
191 }
192
193 fflush(trace_fp);
194 }
195 return NULL;
196 }
197
198 void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)
199 {
200 rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t));
201 }
202
203 void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen)
204 {
205 /* Write string length first */
206 rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen));
207 /* Write actual string now */
208 rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen);
209 }
210
211 int trace_record_start(TraceBufferRecord *rec, uint32_t event, size_t datasize)
212 {
213 unsigned int idx, rec_off, old_idx, new_idx;
214 uint32_t rec_len = sizeof(TraceRecord) + datasize;
215 uint64_t event_u64 = event;
216 uint64_t timestamp_ns = get_clock();
217
218 do {
219 old_idx = g_atomic_int_get(&trace_idx);
220 smp_rmb();
221 new_idx = old_idx + rec_len;
222
223 if (new_idx - writeout_idx > TRACE_BUF_LEN) {
224 /* Trace Buffer Full, Event dropped ! */
225 g_atomic_int_inc(&dropped_events);
226 return -ENOSPC;
227 }
228 } while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));
229
230 idx = old_idx % TRACE_BUF_LEN;
231
232 rec_off = idx;
233 rec_off = write_to_buffer(rec_off, &event_u64, sizeof(event_u64));
234 rec_off = write_to_buffer(rec_off, &timestamp_ns, sizeof(timestamp_ns));
235 rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len));
236 rec_off = write_to_buffer(rec_off, &trace_pid, sizeof(trace_pid));
237
238 rec->tbuf_idx = idx;
239 rec->rec_off = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN;
240 return 0;
241 }
242
243 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size)
244 {
245 uint8_t *data_ptr = dataptr;
246 uint32_t x = 0;
247 while (x < size) {
248 if (idx >= TRACE_BUF_LEN) {
249 idx = idx % TRACE_BUF_LEN;
250 }
251 data_ptr[x++] = trace_buf[idx++];
252 }
253 }
254
255 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size)
256 {
257 uint8_t *data_ptr = dataptr;
258 uint32_t x = 0;
259 while (x < size) {
260 if (idx >= TRACE_BUF_LEN) {
261 idx = idx % TRACE_BUF_LEN;
262 }
263 trace_buf[idx++] = data_ptr[x++];
264 }
265 return idx; /* most callers wants to know where to write next */
266 }
267
268 void trace_record_finish(TraceBufferRecord *rec)
269 {
270 TraceRecord record;
271 read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
272 smp_wmb(); /* write barrier before marking as valid */
273 record.event |= TRACE_RECORD_VALID;
274 write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
275
276 if (((unsigned int)g_atomic_int_get(&trace_idx) - writeout_idx)
277 > TRACE_BUF_FLUSH_THRESHOLD) {
278 flush_trace_file(false);
279 }
280 }
281
282 static int st_write_event_mapping(void)
283 {
284 uint64_t type = TRACE_RECORD_TYPE_MAPPING;
285 TraceEventIter iter;
286 TraceEvent *ev;
287
288 trace_event_iter_init(&iter, NULL);
289 while ((ev = trace_event_iter_next(&iter)) != NULL) {
290 uint64_t id = trace_event_get_id(ev);
291 const char *name = trace_event_get_name(ev);
292 uint32_t len = strlen(name);
293 if (fwrite(&type, sizeof(type), 1, trace_fp) != 1 ||
294 fwrite(&id, sizeof(id), 1, trace_fp) != 1 ||
295 fwrite(&len, sizeof(len), 1, trace_fp) != 1 ||
296 fwrite(name, len, 1, trace_fp) != 1) {
297 return -1;
298 }
299 }
300
301 return 0;
302 }
303
304 void st_set_trace_file_enabled(bool enable)
305 {
306 if (enable == !!trace_fp) {
307 return; /* no change */
308 }
309
310 /* Halt trace writeout */
311 flush_trace_file(true);
312 trace_writeout_enabled = false;
313 flush_trace_file(true);
314
315 if (enable) {
316 static const TraceLogHeader header = {
317 .header_event_id = HEADER_EVENT_ID,
318 .header_magic = HEADER_MAGIC,
319 /* Older log readers will check for version at next location */
320 .header_version = HEADER_VERSION,
321 };
322
323 trace_fp = fopen(trace_file_name, "wb");
324 if (!trace_fp) {
325 return;
326 }
327
328 if (fwrite(&header, sizeof header, 1, trace_fp) != 1 ||
329 st_write_event_mapping() < 0) {
330 fclose(trace_fp);
331 trace_fp = NULL;
332 return;
333 }
334
335 /* Resume trace writeout */
336 trace_writeout_enabled = true;
337 flush_trace_file(false);
338 } else {
339 fclose(trace_fp);
340 trace_fp = NULL;
341 }
342 }
343
344 /**
345 * Set the name of a trace file
346 *
347 * @file The trace file name or NULL for the default name-<pid> set at
348 * config time
349 */
350 void st_set_trace_file(const char *file)
351 {
352 st_set_trace_file_enabled(false);
353
354 g_free(trace_file_name);
355
356 if (!file) {
357 /* Type cast needed for Windows where getpid() returns an int. */
358 trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, (pid_t)getpid());
359 } else {
360 trace_file_name = g_strdup_printf("%s", file);
361 }
362
363 st_set_trace_file_enabled(true);
364 }
365
366 void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
367 {
368 stream_printf(stream, "Trace file \"%s\" %s.\n",
369 trace_file_name, trace_fp ? "on" : "off");
370 }
371
372 void st_flush_trace_buffer(void)
373 {
374 flush_trace_file(true);
375 }
376
377 /* Helper function to create a thread with signals blocked. Use glib's
378 * portable threads since QEMU abstractions cannot be used due to reentrancy in
379 * the tracer. Also note the signal masking on POSIX hosts so that the thread
380 * does not steal signals when the rest of the program wants them blocked.
381 */
382 static GThread *trace_thread_create(GThreadFunc fn)
383 {
384 GThread *thread;
385 #ifndef _WIN32
386 sigset_t set, oldset;
387
388 sigfillset(&set);
389 pthread_sigmask(SIG_SETMASK, &set, &oldset);
390 #endif
391
392 thread = g_thread_new("trace-thread", fn, NULL);
393
394 #ifndef _WIN32
395 pthread_sigmask(SIG_SETMASK, &oldset, NULL);
396 #endif
397
398 return thread;
399 }
400
401 bool st_init(void)
402 {
403 GThread *thread;
404
405 trace_pid = getpid();
406
407 thread = trace_thread_create(writeout_thread);
408 if (!thread) {
409 fprintf(stderr, "warning: unable to initialize simple trace backend\n");
410 return false;
411 }
412
413 atexit(st_flush_trace_buffer);
414 return true;
415 }