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 #include "trace/simple.h"
  23
  24 /** Trace file header event ID */
  25 #define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */
  26
  27 /** Trace file magic number */
  28 #define HEADER_MAGIC 0xf2b177cb0aa429b4ULL
  29
  30 /** Trace file version number, bump if format changes */
  31 #define HEADER_VERSION 2
  32
  33 /** Records were dropped event ID */
  34 #define DROPPED_EVENT_ID (~(uint64_t)0 - 1)
  35
  36 /** Trace record is valid */
  37 #define TRACE_RECORD_VALID ((uint64_t)1 << 63)
  38
  39 /*
  40  * Trace records are written out by a dedicated thread.  The thread waits for
  41  * records to become available, writes them out, and then waits again.
  42  */
  43 #if GLIB_CHECK_VERSION(2, 32, 0)
  44 static GMutex trace_lock;
  45 #define lock_trace_lock() g_mutex_lock(&trace_lock)
  46 #define unlock_trace_lock() g_mutex_unlock(&trace_lock)
  47 #define get_trace_lock_mutex() (&trace_lock)
  48 #else
  49 static GStaticMutex trace_lock = G_STATIC_MUTEX_INIT;
  50 #define lock_trace_lock() g_static_mutex_lock(&trace_lock)
  51 #define unlock_trace_lock() g_static_mutex_unlock(&trace_lock)
  52 #define get_trace_lock_mutex() g_static_mutex_get_mutex(&trace_lock)
  53 #endif
  54
  55 /* g_cond_new() was deprecated in glib 2.31 but we still need to support it */
  56 #if GLIB_CHECK_VERSION(2, 31, 0)
  57 static GCond the_trace_available_cond;
  58 static GCond the_trace_empty_cond;
  59 static GCond *trace_available_cond = &the_trace_available_cond;
  60 static GCond *trace_empty_cond = &the_trace_empty_cond;
  61 #else
  62 static GCond *trace_available_cond;
  63 static GCond *trace_empty_cond;
  64 #endif
  65
  66 static bool trace_available;
  67 static bool trace_writeout_enabled;
  68
  69 enum {
  70     TRACE_BUF_LEN = 4096 * 64,
  71     TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
  72 };
  73
  74 uint8_t trace_buf[TRACE_BUF_LEN];
  75 static volatile gint trace_idx;
  76 static unsigned int writeout_idx;
  77 static volatile gint dropped_events;
  78 static FILE *trace_fp;
  79 static char *trace_file_name;
  80
  81 /* * Trace buffer entry */
  82 typedef struct {
  83     uint64_t event; /*   TraceEventID */
  84     uint64_t timestamp_ns;
  85     uint32_t length;   /*    in bytes */
  86     uint32_t reserved; /*    unused */
  87     uint64_t arguments[];
  88 } TraceRecord;
  89
  90 typedef struct {
  91     uint64_t header_event_id; /* HEADER_EVENT_ID */
  92     uint64_t header_magic;    /* HEADER_MAGIC    */
  93     uint64_t header_version;  /* HEADER_VERSION  */
  94 } TraceLogHeader;
  95
  96
  97 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
  98 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
  99
 100 static void clear_buffer_range(unsigned int idx, size_t len)
 101 {
 102     uint32_t num = 0;
 103     while (num < len) {
 104         if (idx >= TRACE_BUF_LEN) {
 105             idx = idx % TRACE_BUF_LEN;
 106         }
 107         trace_buf[idx++] = 0;
 108         num++;
 109     }
 110 }
 111 /**
 112  * Read a trace record from the trace buffer
 113  *
 114  * @idx         Trace buffer index
 115  * @record      Trace record to fill
 116  *
 117  * Returns false if the record is not valid.
 118  */
 119 static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)
 120 {
 121     uint64_t event_flag = 0;
 122     TraceRecord record;
 123     /* read the event flag to see if its a valid record */
 124     read_from_buffer(idx, &record, sizeof(event_flag));
 125
 126     if (!(record.event & TRACE_RECORD_VALID)) {
 127         return false;
 128     }
 129
 130     smp_rmb(); /* read memory barrier before accessing record */
 131     /* read the record header to know record length */
 132     read_from_buffer(idx, &record, sizeof(TraceRecord));
 133     *recordptr = malloc(record.length); /* dont use g_malloc, can deadlock when traced */
 134     /* make a copy of record to avoid being overwritten */
 135     read_from_buffer(idx, *recordptr, record.length);
 136     smp_rmb(); /* memory barrier before clearing valid flag */
 137     (*recordptr)->event &= ~TRACE_RECORD_VALID;
 138     /* clear the trace buffer range for consumed record otherwise any byte
 139      * with its MSB set may be considered as a valid event id when the writer
 140      * thread crosses this range of buffer again.
 141      */
 142     clear_buffer_range(idx, record.length);
 143     return true;
 144 }
 145
 146 /**
 147  * Kick writeout thread
 148  *
 149  * @wait        Whether to wait for writeout thread to complete
 150  */
 151 static void flush_trace_file(bool wait)
 152 {
 153     lock_trace_lock();
 154     trace_available = true;
 155     g_cond_signal(trace_available_cond);
 156
 157     if (wait) {
 158         g_cond_wait(trace_empty_cond, get_trace_lock_mutex());
 159     }
 160
 161     unlock_trace_lock();
 162 }
 163
 164 static void wait_for_trace_records_available(void)
 165 {
 166     lock_trace_lock();
 167     while (!(trace_available && trace_writeout_enabled)) {
 168         g_cond_signal(trace_empty_cond);
 169         g_cond_wait(trace_available_cond, get_trace_lock_mutex());
 170     }
 171     trace_available = false;
 172     unlock_trace_lock();
 173 }
 174
 175 static gpointer writeout_thread(gpointer opaque)
 176 {
 177     TraceRecord *recordptr;
 178     union {
 179         TraceRecord rec;
 180         uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];
 181     } dropped;
 182     unsigned int idx = 0;
 183     int dropped_count;
 184     size_t unused __attribute__ ((unused));
 185
 186     for (;;) {
 187         wait_for_trace_records_available();
 188
 189         if (g_atomic_int_get(&dropped_events)) {
 190             dropped.rec.event = DROPPED_EVENT_ID,
 191             dropped.rec.timestamp_ns = get_clock();
 192             dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
 193             dropped.rec.reserved = 0;
 194             do {
 195                 dropped_count = g_atomic_int_get(&dropped_events);
 196             } while (!g_atomic_int_compare_and_exchange(&dropped_events,
 197                                                         dropped_count, 0));
 198             dropped.rec.arguments[0] = dropped_count;
 199             unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
 200         }
 201
 202         while (get_trace_record(idx, &recordptr)) {
 203             unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
 204             writeout_idx += recordptr->length;
 205             free(recordptr); /* dont use g_free, can deadlock when traced */
 206             idx = writeout_idx % TRACE_BUF_LEN;
 207         }
 208
 209         fflush(trace_fp);
 210     }
 211     return NULL;
 212 }
 213
 214 void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)
 215 {
 216     rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t));
 217 }
 218
 219 void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen)
 220 {
 221     /* Write string length first */
 222     rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen));
 223     /* Write actual string now */
 224     rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen);
 225 }
 226
 227 int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasize)
 228 {
 229     unsigned int idx, rec_off, old_idx, new_idx;
 230     uint32_t rec_len = sizeof(TraceRecord) + datasize;
 231     uint64_t event_u64 = event;
 232     uint64_t timestamp_ns = get_clock();
 233
 234     do {
 235         old_idx = g_atomic_int_get(&trace_idx);
 236         smp_rmb();
 237         new_idx = old_idx + rec_len;
 238
 239         if (new_idx - writeout_idx > TRACE_BUF_LEN) {
 240             /* Trace Buffer Full, Event dropped ! */
 241             g_atomic_int_inc(&dropped_events);
 242             return -ENOSPC;
 243         }
 244     } while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));
 245
 246     idx = old_idx % TRACE_BUF_LEN;
 247
 248     rec_off = idx;
 249     rec_off = write_to_buffer(rec_off, &event_u64, sizeof(event_u64));
 250     rec_off = write_to_buffer(rec_off, &timestamp_ns, sizeof(timestamp_ns));
 251     rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len));
 252
 253     rec->tbuf_idx = idx;
 254     rec->rec_off  = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN;
 255     return 0;
 256 }
 257
 258 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size)
 259 {
 260     uint8_t *data_ptr = dataptr;
 261     uint32_t x = 0;
 262     while (x < size) {
 263         if (idx >= TRACE_BUF_LEN) {
 264             idx = idx % TRACE_BUF_LEN;
 265         }
 266         data_ptr[x++] = trace_buf[idx++];
 267     }
 268 }
 269
 270 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size)
 271 {
 272     uint8_t *data_ptr = dataptr;
 273     uint32_t x = 0;
 274     while (x < size) {
 275         if (idx >= TRACE_BUF_LEN) {
 276             idx = idx % TRACE_BUF_LEN;
 277         }
 278         trace_buf[idx++] = data_ptr[x++];
 279     }
 280     return idx; /* most callers wants to know where to write next */
 281 }
 282
 283 void trace_record_finish(TraceBufferRecord *rec)
 284 {
 285     TraceRecord record;
 286     read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
 287     smp_wmb(); /* write barrier before marking as valid */
 288     record.event |= TRACE_RECORD_VALID;
 289     write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
 290
 291     if (((unsigned int)g_atomic_int_get(&trace_idx) - writeout_idx)
 292         > TRACE_BUF_FLUSH_THRESHOLD) {
 293         flush_trace_file(false);
 294     }
 295 }
 296
 297 void st_set_trace_file_enabled(bool enable)
 298 {
 299     if (enable == !!trace_fp) {
 300         return; /* no change */
 301     }
 302
 303     /* Halt trace writeout */
 304     flush_trace_file(true);
 305     trace_writeout_enabled = false;
 306     flush_trace_file(true);
 307
 308     if (enable) {
 309         static const TraceLogHeader header = {
 310             .header_event_id = HEADER_EVENT_ID,
 311             .header_magic = HEADER_MAGIC,
 312             /* Older log readers will check for version at next location */
 313             .header_version = HEADER_VERSION,
 314         };
 315
 316         trace_fp = fopen(trace_file_name, "wb");
 317         if (!trace_fp) {
 318             return;
 319         }
 320
 321         if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {
 322             fclose(trace_fp);
 323             trace_fp = NULL;
 324             return;
 325         }
 326
 327         /* Resume trace writeout */
 328         trace_writeout_enabled = true;
 329         flush_trace_file(false);
 330     } else {
 331         fclose(trace_fp);
 332         trace_fp = NULL;
 333     }
 334 }
 335
 336 /**
 337  * Set the name of a trace file
 338  *
 339  * @file        The trace file name or NULL for the default name-<pid> set at
 340  *              config time
 341  */
 342 bool st_set_trace_file(const char *file)
 343 {
 344     st_set_trace_file_enabled(false);
 345
 346     g_free(trace_file_name);
 347
 348     if (!file) {
 349         trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, getpid());
 350     } else {
 351         trace_file_name = g_strdup_printf("%s", file);
 352     }
 353
 354     st_set_trace_file_enabled(true);
 355     return true;
 356 }
 357
 358 void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
 359 {
 360     stream_printf(stream, "Trace file \"%s\" %s.\n",
 361                   trace_file_name, trace_fp ? "on" : "off");
 362 }
 363
 364 void st_flush_trace_buffer(void)
 365 {
 366     flush_trace_file(true);
 367 }
 368
 369 void trace_print_events(FILE *stream, fprintf_function stream_printf)
 370 {
 371     unsigned int i;
 372
 373     for (i = 0; i < trace_event_count(); i++) {
 374         TraceEvent *ev = trace_event_id(i);
 375         stream_printf(stream, "%s [Event ID %u] : state %u\n",
 376                       trace_event_get_name(ev), i, trace_event_get_state_dynamic(ev));
 377     }
 378 }
 379
 380 void trace_event_set_state_dynamic_backend(TraceEvent *ev, bool state)
 381 {
 382     ev->dstate = state;
 383 }
 384
 385 /* Helper function to create a thread with signals blocked.  Use glib's
 386  * portable threads since QEMU abstractions cannot be used due to reentrancy in
 387  * the tracer.  Also note the signal masking on POSIX hosts so that the thread
 388  * does not steal signals when the rest of the program wants them blocked.
 389  */
 390 static GThread *trace_thread_create(GThreadFunc fn)
 391 {
 392     GThread *thread;
 393 #ifndef _WIN32
 394     sigset_t set, oldset;
 395
 396     sigfillset(&set);
 397     pthread_sigmask(SIG_SETMASK, &set, &oldset);
 398 #endif
 399
 400 #if GLIB_CHECK_VERSION(2, 31, 0)
 401     thread = g_thread_new("trace-thread", fn, NULL);
 402 #else
 403     thread = g_thread_create(fn, NULL, FALSE, NULL);
 404 #endif
 405
 406 #ifndef _WIN32
 407     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 408 #endif
 409
 410     return thread;
 411 }
 412
 413 bool trace_backend_init(const char *events, const char *file)
 414 {
 415     GThread *thread;
 416
 417 #if !GLIB_CHECK_VERSION(2, 31, 0)
 418     trace_available_cond = g_cond_new();
 419     trace_empty_cond = g_cond_new();
 420 #endif
 421
 422     thread = trace_thread_create(writeout_thread);
 423     if (!thread) {
 424         fprintf(stderr, "warning: unable to initialize simple trace backend\n");
 425         return false;
 426     }
 427
 428     atexit(st_flush_trace_buffer);
 429     trace_backend_init_events(events);
 430     st_set_trace_file(file);
 431     return true;
 432 }