vmsvga: don't process more than 1024 fifo commands at once
[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 */
21 #define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */
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 3
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 /* * Trace buffer entry */
60 typedef struct {
61 uint64_t event; /* TraceEventID */
62 uint64_t timestamp_ns;
63 uint32_t length; /* in bytes */
64 uint32_t pid;
65 uint64_t arguments[];
66 } TraceRecord;
67
68 typedef struct {
69 uint64_t header_event_id; /* HEADER_EVENT_ID */
70 uint64_t header_magic; /* HEADER_MAGIC */
71 uint64_t header_version; /* HEADER_VERSION */
72 } TraceLogHeader;
73
74
75 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
76 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
77
78 static void clear_buffer_range(unsigned int idx, size_t len)
79 {
80 uint32_t num = 0;
81 while (num < len) {
82 if (idx >= TRACE_BUF_LEN) {
83 idx = idx % TRACE_BUF_LEN;
84 }
85 trace_buf[idx++] = 0;
86 num++;
87 }
88 }
89 /**
90 * Read a trace record from the trace buffer
91 *
92 * @idx Trace buffer index
93 * @record Trace record to fill
94 *
95 * Returns false if the record is not valid.
96 */
97 static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)
98 {
99 uint64_t event_flag = 0;
100 TraceRecord record;
101 /* read the event flag to see if its a valid record */
102 read_from_buffer(idx, &record, sizeof(event_flag));
103
104 if (!(record.event & TRACE_RECORD_VALID)) {
105 return false;
106 }
107
108 smp_rmb(); /* read memory barrier before accessing record */
109 /* read the record header to know record length */
110 read_from_buffer(idx, &record, sizeof(TraceRecord));
111 *recordptr = malloc(record.length); /* don't use g_malloc, can deadlock when traced */
112 /* make a copy of record to avoid being overwritten */
113 read_from_buffer(idx, *recordptr, record.length);
114 smp_rmb(); /* memory barrier before clearing valid flag */
115 (*recordptr)->event &= ~TRACE_RECORD_VALID;
116 /* clear the trace buffer range for consumed record otherwise any byte
117 * with its MSB set may be considered as a valid event id when the writer
118 * thread crosses this range of buffer again.
119 */
120 clear_buffer_range(idx, record.length);
121 return true;
122 }
123
124 /**
125 * Kick writeout thread
126 *
127 * @wait Whether to wait for writeout thread to complete
128 */
129 static void flush_trace_file(bool wait)
130 {
131 g_mutex_lock(&trace_lock);
132 trace_available = true;
133 g_cond_signal(&trace_available_cond);
134
135 if (wait) {
136 g_cond_wait(&trace_empty_cond, &trace_lock);
137 }
138
139 g_mutex_unlock(&trace_lock);
140 }
141
142 static void wait_for_trace_records_available(void)
143 {
144 g_mutex_lock(&trace_lock);
145 while (!(trace_available && trace_writeout_enabled)) {
146 g_cond_signal(&trace_empty_cond);
147 g_cond_wait(&trace_available_cond, &trace_lock);
148 }
149 trace_available = false;
150 g_mutex_unlock(&trace_lock);
151 }
152
153 static gpointer writeout_thread(gpointer opaque)
154 {
155 TraceRecord *recordptr;
156 union {
157 TraceRecord rec;
158 uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];
159 } dropped;
160 unsigned int idx = 0;
161 int dropped_count;
162 size_t unused __attribute__ ((unused));
163
164 for (;;) {
165 wait_for_trace_records_available();
166
167 if (g_atomic_int_get(&dropped_events)) {
168 dropped.rec.event = DROPPED_EVENT_ID,
169 dropped.rec.timestamp_ns = get_clock();
170 dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
171 dropped.rec.pid = trace_pid;
172 do {
173 dropped_count = g_atomic_int_get(&dropped_events);
174 } while (!g_atomic_int_compare_and_exchange(&dropped_events,
175 dropped_count, 0));
176 dropped.rec.arguments[0] = dropped_count;
177 unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
178 }
179
180 while (get_trace_record(idx, &recordptr)) {
181 unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
182 writeout_idx += recordptr->length;
183 free(recordptr); /* don't use g_free, can deadlock when traced */
184 idx = writeout_idx % TRACE_BUF_LEN;
185 }
186
187 fflush(trace_fp);
188 }
189 return NULL;
190 }
191
192 void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)
193 {
194 rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t));
195 }
196
197 void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen)
198 {
199 /* Write string length first */
200 rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen));
201 /* Write actual string now */
202 rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen);
203 }
204
205 int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasize)
206 {
207 unsigned int idx, rec_off, old_idx, new_idx;
208 uint32_t rec_len = sizeof(TraceRecord) + datasize;
209 uint64_t event_u64 = event;
210 uint64_t timestamp_ns = get_clock();
211
212 do {
213 old_idx = g_atomic_int_get(&trace_idx);
214 smp_rmb();
215 new_idx = old_idx + rec_len;
216
217 if (new_idx - writeout_idx > TRACE_BUF_LEN) {
218 /* Trace Buffer Full, Event dropped ! */
219 g_atomic_int_inc(&dropped_events);
220 return -ENOSPC;
221 }
222 } while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));
223
224 idx = old_idx % TRACE_BUF_LEN;
225
226 rec_off = idx;
227 rec_off = write_to_buffer(rec_off, &event_u64, sizeof(event_u64));
228 rec_off = write_to_buffer(rec_off, &timestamp_ns, sizeof(timestamp_ns));
229 rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len));
230 rec_off = write_to_buffer(rec_off, &trace_pid, sizeof(trace_pid));
231
232 rec->tbuf_idx = idx;
233 rec->rec_off = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN;
234 return 0;
235 }
236
237 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size)
238 {
239 uint8_t *data_ptr = dataptr;
240 uint32_t x = 0;
241 while (x < size) {
242 if (idx >= TRACE_BUF_LEN) {
243 idx = idx % TRACE_BUF_LEN;
244 }
245 data_ptr[x++] = trace_buf[idx++];
246 }
247 }
248
249 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size)
250 {
251 uint8_t *data_ptr = dataptr;
252 uint32_t x = 0;
253 while (x < size) {
254 if (idx >= TRACE_BUF_LEN) {
255 idx = idx % TRACE_BUF_LEN;
256 }
257 trace_buf[idx++] = data_ptr[x++];
258 }
259 return idx; /* most callers wants to know where to write next */
260 }
261
262 void trace_record_finish(TraceBufferRecord *rec)
263 {
264 TraceRecord record;
265 read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
266 smp_wmb(); /* write barrier before marking as valid */
267 record.event |= TRACE_RECORD_VALID;
268 write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
269
270 if (((unsigned int)g_atomic_int_get(&trace_idx) - writeout_idx)
271 > TRACE_BUF_FLUSH_THRESHOLD) {
272 flush_trace_file(false);
273 }
274 }
275
276 void st_set_trace_file_enabled(bool enable)
277 {
278 if (enable == !!trace_fp) {
279 return; /* no change */
280 }
281
282 /* Halt trace writeout */
283 flush_trace_file(true);
284 trace_writeout_enabled = false;
285 flush_trace_file(true);
286
287 if (enable) {
288 static const TraceLogHeader header = {
289 .header_event_id = HEADER_EVENT_ID,
290 .header_magic = HEADER_MAGIC,
291 /* Older log readers will check for version at next location */
292 .header_version = HEADER_VERSION,
293 };
294
295 trace_fp = fopen(trace_file_name, "wb");
296 if (!trace_fp) {
297 return;
298 }
299
300 if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {
301 fclose(trace_fp);
302 trace_fp = NULL;
303 return;
304 }
305
306 /* Resume trace writeout */
307 trace_writeout_enabled = true;
308 flush_trace_file(false);
309 } else {
310 fclose(trace_fp);
311 trace_fp = NULL;
312 }
313 }
314
315 /**
316 * Set the name of a trace file
317 *
318 * @file The trace file name or NULL for the default name-<pid> set at
319 * config time
320 */
321 void st_set_trace_file(const char *file)
322 {
323 st_set_trace_file_enabled(false);
324
325 g_free(trace_file_name);
326
327 if (!file) {
328 /* Type cast needed for Windows where getpid() returns an int. */
329 trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, (pid_t)getpid());
330 } else {
331 trace_file_name = g_strdup_printf("%s", file);
332 }
333
334 st_set_trace_file_enabled(true);
335 }
336
337 void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
338 {
339 stream_printf(stream, "Trace file \"%s\" %s.\n",
340 trace_file_name, trace_fp ? "on" : "off");
341 }
342
343 void st_flush_trace_buffer(void)
344 {
345 flush_trace_file(true);
346 }
347
348 /* Helper function to create a thread with signals blocked. Use glib's
349 * portable threads since QEMU abstractions cannot be used due to reentrancy in
350 * the tracer. Also note the signal masking on POSIX hosts so that the thread
351 * does not steal signals when the rest of the program wants them blocked.
352 */
353 static GThread *trace_thread_create(GThreadFunc fn)
354 {
355 GThread *thread;
356 #ifndef _WIN32
357 sigset_t set, oldset;
358
359 sigfillset(&set);
360 pthread_sigmask(SIG_SETMASK, &set, &oldset);
361 #endif
362
363 thread = g_thread_new("trace-thread", fn, NULL);
364
365 #ifndef _WIN32
366 pthread_sigmask(SIG_SETMASK, &oldset, NULL);
367 #endif
368
369 return thread;
370 }
371
372 bool st_init(void)
373 {
374 GThread *thread;
375
376 trace_pid = getpid();
377
378 thread = trace_thread_create(writeout_thread);
379 if (!thread) {
380 fprintf(stderr, "warning: unable to initialize simple trace backend\n");
381 return false;
382 }
383
384 atexit(st_flush_trace_buffer);
385 return true;
386 }