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 <stdlib.h>
  12 #include <stdint.h>
  13 #include <stdio.h>
  14 #include <time.h>
  15 #ifndef _WIN32
  16 #include <signal.h>
  17 #include <pthread.h>
  18 #endif
  19 #include "qemu/timer.h"
  20 #include "trace.h"
  21 #include "trace/control.h"
  22
  23 /** Trace file header event ID */
  24 #define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */
  25
  26 /** Trace file magic number */
  27 #define HEADER_MAGIC 0xf2b177cb0aa429b4ULL
  28
  29 /** Trace file version number, bump if format changes */
  30 #define HEADER_VERSION 2
  31
  32 /** Records were dropped event ID */
  33 #define DROPPED_EVENT_ID (~(uint64_t)0 - 1)
  34
  35 /** Trace record is valid */
  36 #define TRACE_RECORD_VALID ((uint64_t)1 << 63)
  37
  38 /*
  39  * Trace records are written out by a dedicated thread.  The thread waits for
  40  * records to become available, writes them out, and then waits again.
  41  */
  42 static GStaticMutex trace_lock = G_STATIC_MUTEX_INIT;
  43 static GCond *trace_available_cond;
  44 static GCond *trace_empty_cond;
  45 static bool trace_available;
  46 static bool trace_writeout_enabled;
  47
  48 enum {
  49     TRACE_BUF_LEN = 4096 * 64,
  50     TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
  51 };
  52
  53 uint8_t trace_buf[TRACE_BUF_LEN];
  54 static unsigned int trace_idx;
  55 static unsigned int writeout_idx;
  56 static uint64_t dropped_events;
  57 static FILE *trace_fp;
  58 static char *trace_file_name;
  59
  60 /* * Trace buffer entry */
  61 typedef struct {
  62     uint64_t event; /*   TraceEventID */
  63     uint64_t timestamp_ns;
  64     uint32_t length;   /*    in bytes */
  65     uint32_t reserved; /*    unused */
  66     uint8_t arguments[];
  67 } TraceRecord;
  68
  69 typedef struct {
  70     uint64_t header_event_id; /* HEADER_EVENT_ID */
  71     uint64_t header_magic;    /* HEADER_MAGIC    */
  72     uint64_t header_version;  /* HEADER_VERSION  */
  73 } TraceLogHeader;
  74
  75
  76 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
  77 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
  78
  79 static void clear_buffer_range(unsigned int idx, size_t len)
  80 {
  81     uint32_t num = 0;
  82     while (num < len) {
  83         if (idx >= TRACE_BUF_LEN) {
  84             idx = idx % TRACE_BUF_LEN;
  85         }
  86         trace_buf[idx++] = 0;
  87         num++;
  88     }
  89 }
  90 /**
  91  * Read a trace record from the trace buffer
  92  *
  93  * @idx         Trace buffer index
  94  * @record      Trace record to fill
  95  *
  96  * Returns false if the record is not valid.
  97  */
  98 static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)
  99 {
 100     uint64_t event_flag = 0;
 101     TraceRecord record;
 102     /* read the event flag to see if its a valid record */
 103     read_from_buffer(idx, &record, sizeof(event_flag));
 104
 105     if (!(record.event & TRACE_RECORD_VALID)) {
 106         return false;
 107     }
 108
 109     smp_rmb(); /* read memory barrier before accessing record */
 110     /* read the record header to know record length */
 111     read_from_buffer(idx, &record, sizeof(TraceRecord));
 112     *recordptr = malloc(record.length); /* dont use g_malloc, can deadlock when traced */
 113     /* make a copy of record to avoid being overwritten */
 114     read_from_buffer(idx, *recordptr, record.length);
 115     smp_rmb(); /* memory barrier before clearing valid flag */
 116     (*recordptr)->event &= ~TRACE_RECORD_VALID;
 117     /* clear the trace buffer range for consumed record otherwise any byte
 118      * with its MSB set may be considered as a valid event id when the writer
 119      * thread crosses this range of buffer again.
 120      */
 121     clear_buffer_range(idx, record.length);
 122     return true;
 123 }
 124
 125 /**
 126  * Kick writeout thread
 127  *
 128  * @wait        Whether to wait for writeout thread to complete
 129  */
 130 static void flush_trace_file(bool wait)
 131 {
 132     g_static_mutex_lock(&trace_lock);
 133     trace_available = true;
 134     g_cond_signal(trace_available_cond);
 135
 136     if (wait) {
 137         g_cond_wait(trace_empty_cond, g_static_mutex_get_mutex(&trace_lock));
 138     }
 139
 140     g_static_mutex_unlock(&trace_lock);
 141 }
 142
 143 static void wait_for_trace_records_available(void)
 144 {
 145     g_static_mutex_lock(&trace_lock);
 146     while (!(trace_available && trace_writeout_enabled)) {
 147         g_cond_signal(trace_empty_cond);
 148         g_cond_wait(trace_available_cond,
 149                     g_static_mutex_get_mutex(&trace_lock));
 150     }
 151     trace_available = false;
 152     g_static_mutex_unlock(&trace_lock);
 153 }
 154
 155 static gpointer writeout_thread(gpointer opaque)
 156 {
 157     TraceRecord *recordptr;
 158     union {
 159         TraceRecord rec;
 160         uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];
 161     } dropped;
 162     unsigned int idx = 0;
 163     uint64_t dropped_count;
 164     size_t unused __attribute__ ((unused));
 165
 166     for (;;) {
 167         wait_for_trace_records_available();
 168
 169         if (dropped_events) {
 170             dropped.rec.event = DROPPED_EVENT_ID,
 171             dropped.rec.timestamp_ns = get_clock();
 172             dropped.rec.length = sizeof(TraceRecord) + sizeof(dropped_events),
 173             dropped.rec.reserved = 0;
 174             while (1) {
 175                 dropped_count = dropped_events;
 176                 if (g_atomic_int_compare_and_exchange((gint *)&dropped_events,
 177                                                       dropped_count, 0)) {
 178                     break;
 179                 }
 180             }
 181             memcpy(dropped.rec.arguments, &dropped_count, sizeof(uint64_t));
 182             unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
 183         }
 184
 185         while (get_trace_record(idx, &recordptr)) {
 186             unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
 187             writeout_idx += recordptr->length;
 188             free(recordptr); /* dont use g_free, can deadlock when traced */
 189             idx = writeout_idx % TRACE_BUF_LEN;
 190         }
 191
 192         fflush(trace_fp);
 193     }
 194     return NULL;
 195 }
 196
 197 void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)
 198 {
 199     rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t));
 200 }
 201
 202 void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen)
 203 {
 204     /* Write string length first */
 205     rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen));
 206     /* Write actual string now */
 207     rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen);
 208 }
 209
 210 int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasize)
 211 {
 212     unsigned int idx, rec_off, old_idx, new_idx;
 213     uint32_t rec_len = sizeof(TraceRecord) + datasize;
 214     uint64_t timestamp_ns = get_clock();
 215
 216     while (1) {
 217         old_idx = trace_idx;
 218         smp_rmb();
 219         new_idx = old_idx + rec_len;
 220
 221         if (new_idx - writeout_idx > TRACE_BUF_LEN) {
 222             /* Trace Buffer Full, Event dropped ! */
 223             g_atomic_int_inc((gint *)&dropped_events);
 224             return -ENOSPC;
 225         }
 226
 227         if (g_atomic_int_compare_and_exchange((gint *)&trace_idx,
 228                                               old_idx, new_idx)) {
 229             break;
 230         }
 231     }
 232
 233     idx = old_idx % TRACE_BUF_LEN;
 234
 235     rec_off = idx;
 236     rec_off = write_to_buffer(rec_off, &event, sizeof(event));
 237     rec_off = write_to_buffer(rec_off, &timestamp_ns, sizeof(timestamp_ns));
 238     rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len));
 239
 240     rec->tbuf_idx = idx;
 241     rec->rec_off  = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN;
 242     return 0;
 243 }
 244
 245 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size)
 246 {
 247     uint8_t *data_ptr = dataptr;
 248     uint32_t x = 0;
 249     while (x < size) {
 250         if (idx >= TRACE_BUF_LEN) {
 251             idx = idx % TRACE_BUF_LEN;
 252         }
 253         data_ptr[x++] = trace_buf[idx++];
 254     }
 255 }
 256
 257 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size)
 258 {
 259     uint8_t *data_ptr = dataptr;
 260     uint32_t x = 0;
 261     while (x < size) {
 262         if (idx >= TRACE_BUF_LEN) {
 263             idx = idx % TRACE_BUF_LEN;
 264         }
 265         trace_buf[idx++] = data_ptr[x++];
 266     }
 267     return idx; /* most callers wants to know where to write next */
 268 }
 269
 270 void trace_record_finish(TraceBufferRecord *rec)
 271 {
 272     TraceRecord record;
 273     read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
 274     smp_wmb(); /* write barrier before marking as valid */
 275     record.event |= TRACE_RECORD_VALID;
 276     write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
 277
 278     if ((trace_idx - writeout_idx) > TRACE_BUF_FLUSH_THRESHOLD) {
 279         flush_trace_file(false);
 280     }
 281 }
 282
 283 void st_set_trace_file_enabled(bool enable)
 284 {
 285     if (enable == !!trace_fp) {
 286         return; /* no change */
 287     }
 288
 289     /* Halt trace writeout */
 290     flush_trace_file(true);
 291     trace_writeout_enabled = false;
 292     flush_trace_file(true);
 293
 294     if (enable) {
 295         static const TraceLogHeader header = {
 296             .header_event_id = HEADER_EVENT_ID,
 297             .header_magic = HEADER_MAGIC,
 298             /* Older log readers will check for version at next location */
 299             .header_version = HEADER_VERSION,
 300         };
 301
 302         trace_fp = fopen(trace_file_name, "wb");
 303         if (!trace_fp) {
 304             return;
 305         }
 306
 307         if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {
 308             fclose(trace_fp);
 309             trace_fp = NULL;
 310             return;
 311         }
 312
 313         /* Resume trace writeout */
 314         trace_writeout_enabled = true;
 315         flush_trace_file(false);
 316     } else {
 317         fclose(trace_fp);
 318         trace_fp = NULL;
 319     }
 320 }
 321
 322 /**
 323  * Set the name of a trace file
 324  *
 325  * @file        The trace file name or NULL for the default name-<pid> set at
 326  *              config time
 327  */
 328 bool st_set_trace_file(const char *file)
 329 {
 330     st_set_trace_file_enabled(false);
 331
 332     g_free(trace_file_name);
 333
 334     if (!file) {
 335         trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, getpid());
 336     } else {
 337         trace_file_name = g_strdup_printf("%s", file);
 338     }
 339
 340     st_set_trace_file_enabled(true);
 341     return true;
 342 }
 343
 344 void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
 345 {
 346     stream_printf(stream, "Trace file \"%s\" %s.\n",
 347                   trace_file_name, trace_fp ? "on" : "off");
 348 }
 349
 350 void st_flush_trace_buffer(void)
 351 {
 352     flush_trace_file(true);
 353 }
 354
 355 void trace_print_events(FILE *stream, fprintf_function stream_printf)
 356 {
 357     unsigned int i;
 358
 359     for (i = 0; i < NR_TRACE_EVENTS; i++) {
 360         stream_printf(stream, "%s [Event ID %u] : state %u\n",
 361                       trace_list[i].tp_name, i, trace_list[i].state);
 362     }
 363 }
 364
 365 bool trace_event_set_state(const char *name, bool state)
 366 {
 367     unsigned int i;
 368     unsigned int len;
 369     bool wildcard = false;
 370     bool matched = false;
 371
 372     len = strlen(name);
 373     if (len > 0 && name[len - 1] == '*') {
 374         wildcard = true;
 375         len -= 1;
 376     }
 377     for (i = 0; i < NR_TRACE_EVENTS; i++) {
 378         if (wildcard) {
 379             if (!strncmp(trace_list[i].tp_name, name, len)) {
 380                 trace_list[i].state = state;
 381                 matched = true;
 382             }
 383             continue;
 384         }
 385         if (!strcmp(trace_list[i].tp_name, name)) {
 386             trace_list[i].state = state;
 387             return true;
 388         }
 389     }
 390     return matched;
 391 }
 392
 393 /* Helper function to create a thread with signals blocked.  Use glib's
 394  * portable threads since QEMU abstractions cannot be used due to reentrancy in
 395  * the tracer.  Also note the signal masking on POSIX hosts so that the thread
 396  * does not steal signals when the rest of the program wants them blocked.
 397  */
 398 static GThread *trace_thread_create(GThreadFunc fn)
 399 {
 400     GThread *thread;
 401 #ifndef _WIN32
 402     sigset_t set, oldset;
 403
 404     sigfillset(&set);
 405     pthread_sigmask(SIG_SETMASK, &set, &oldset);
 406 #endif
 407     thread = g_thread_create(fn, NULL, FALSE, NULL);
 408 #ifndef _WIN32
 409     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 410 #endif
 411
 412     return thread;
 413 }
 414
 415 bool trace_backend_init(const char *events, const char *file)
 416 {
 417     GThread *thread;
 418
 419     if (!g_thread_supported()) {
 420 #if !GLIB_CHECK_VERSION(2, 31, 0)
 421         g_thread_init(NULL);
 422 #else
 423         fprintf(stderr, "glib threading failed to initialize.\n");
 424         exit(1);
 425 #endif
 426     }
 427
 428     trace_available_cond = g_cond_new();
 429     trace_empty_cond = g_cond_new();
 430
 431     thread = trace_thread_create(writeout_thread);
 432     if (!thread) {
 433         fprintf(stderr, "warning: unable to initialize simple trace backend\n");
 434         return false;
 435     }
 436
 437     atexit(st_flush_trace_buffer);
 438     trace_backend_init_events(events);
 439     st_set_trace_file(file);
 440     return true;
 441 }