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 3
  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 uint32_t trace_pid;
  79 static FILE *trace_fp;
  80 static char *trace_file_name;
  81
  82 /* * Trace buffer entry */
  83 typedef struct {
  84     uint64_t event; /*   TraceEventID */
  85     uint64_t timestamp_ns;
  86     uint32_t length;   /*    in bytes */
  87     uint32_t pid;
  88     uint64_t arguments[];
  89 } TraceRecord;
  90
  91 typedef struct {
  92     uint64_t header_event_id; /* HEADER_EVENT_ID */
  93     uint64_t header_magic;    /* HEADER_MAGIC    */
  94     uint64_t header_version;  /* HEADER_VERSION  */
  95 } TraceLogHeader;
  96
  97
  98 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
  99 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
 100
 101 static void clear_buffer_range(unsigned int idx, size_t len)
 102 {
 103     uint32_t num = 0;
 104     while (num < len) {
 105         if (idx >= TRACE_BUF_LEN) {
 106             idx = idx % TRACE_BUF_LEN;
 107         }
 108         trace_buf[idx++] = 0;
 109         num++;
 110     }
 111 }
 112 /**
 113  * Read a trace record from the trace buffer
 114  *
 115  * @idx         Trace buffer index
 116  * @record      Trace record to fill
 117  *
 118  * Returns false if the record is not valid.
 119  */
 120 static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)
 121 {
 122     uint64_t event_flag = 0;
 123     TraceRecord record;
 124     /* read the event flag to see if its a valid record */
 125     read_from_buffer(idx, &record, sizeof(event_flag));
 126
 127     if (!(record.event & TRACE_RECORD_VALID)) {
 128         return false;
 129     }
 130
 131     smp_rmb(); /* read memory barrier before accessing record */
 132     /* read the record header to know record length */
 133     read_from_buffer(idx, &record, sizeof(TraceRecord));
 134     *recordptr = malloc(record.length); /* dont use g_malloc, can deadlock when traced */
 135     /* make a copy of record to avoid being overwritten */
 136     read_from_buffer(idx, *recordptr, record.length);
 137     smp_rmb(); /* memory barrier before clearing valid flag */
 138     (*recordptr)->event &= ~TRACE_RECORD_VALID;
 139     /* clear the trace buffer range for consumed record otherwise any byte
 140      * with its MSB set may be considered as a valid event id when the writer
 141      * thread crosses this range of buffer again.
 142      */
 143     clear_buffer_range(idx, record.length);
 144     return true;
 145 }
 146
 147 /**
 148  * Kick writeout thread
 149  *
 150  * @wait        Whether to wait for writeout thread to complete
 151  */
 152 static void flush_trace_file(bool wait)
 153 {
 154     lock_trace_lock();
 155     trace_available = true;
 156     g_cond_signal(trace_available_cond);
 157
 158     if (wait) {
 159         g_cond_wait(trace_empty_cond, get_trace_lock_mutex());
 160     }
 161
 162     unlock_trace_lock();
 163 }
 164
 165 static void wait_for_trace_records_available(void)
 166 {
 167     lock_trace_lock();
 168     while (!(trace_available && trace_writeout_enabled)) {
 169         g_cond_signal(trace_empty_cond);
 170         g_cond_wait(trace_available_cond, get_trace_lock_mutex());
 171     }
 172     trace_available = false;
 173     unlock_trace_lock();
 174 }
 175
 176 static gpointer writeout_thread(gpointer opaque)
 177 {
 178     TraceRecord *recordptr;
 179     union {
 180         TraceRecord rec;
 181         uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];
 182     } dropped;
 183     unsigned int idx = 0;
 184     int dropped_count;
 185     size_t unused __attribute__ ((unused));
 186
 187     for (;;) {
 188         wait_for_trace_records_available();
 189
 190         if (g_atomic_int_get(&dropped_events)) {
 191             dropped.rec.event = DROPPED_EVENT_ID,
 192             dropped.rec.timestamp_ns = get_clock();
 193             dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
 194             dropped.rec.pid = trace_pid;
 195             do {
 196                 dropped_count = g_atomic_int_get(&dropped_events);
 197             } while (!g_atomic_int_compare_and_exchange(&dropped_events,
 198                                                         dropped_count, 0));
 199             dropped.rec.arguments[0] = dropped_count;
 200             unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
 201         }
 202
 203         while (get_trace_record(idx, &recordptr)) {
 204             unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
 205             writeout_idx += recordptr->length;
 206             free(recordptr); /* dont use g_free, can deadlock when traced */
 207             idx = writeout_idx % TRACE_BUF_LEN;
 208         }
 209
 210         fflush(trace_fp);
 211     }
 212     return NULL;
 213 }
 214
 215 void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)
 216 {
 217     rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t));
 218 }
 219
 220 void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen)
 221 {
 222     /* Write string length first */
 223     rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen));
 224     /* Write actual string now */
 225     rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen);
 226 }
 227
 228 int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasize)
 229 {
 230     unsigned int idx, rec_off, old_idx, new_idx;
 231     uint32_t rec_len = sizeof(TraceRecord) + datasize;
 232     uint64_t event_u64 = event;
 233     uint64_t timestamp_ns = get_clock();
 234
 235     do {
 236         old_idx = g_atomic_int_get(&trace_idx);
 237         smp_rmb();
 238         new_idx = old_idx + rec_len;
 239
 240         if (new_idx - writeout_idx > TRACE_BUF_LEN) {
 241             /* Trace Buffer Full, Event dropped ! */
 242             g_atomic_int_inc(&dropped_events);
 243             return -ENOSPC;
 244         }
 245     } while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));
 246
 247     idx = old_idx % TRACE_BUF_LEN;
 248
 249     rec_off = idx;
 250     rec_off = write_to_buffer(rec_off, &event_u64, sizeof(event_u64));
 251     rec_off = write_to_buffer(rec_off, &timestamp_ns, sizeof(timestamp_ns));
 252     rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len));
 253     rec_off = write_to_buffer(rec_off, &trace_pid, sizeof(trace_pid));
 254
 255     rec->tbuf_idx = idx;
 256     rec->rec_off  = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN;
 257     return 0;
 258 }
 259
 260 static void read_from_buffer(unsigned int idx, void *dataptr, size_t size)
 261 {
 262     uint8_t *data_ptr = dataptr;
 263     uint32_t x = 0;
 264     while (x < size) {
 265         if (idx >= TRACE_BUF_LEN) {
 266             idx = idx % TRACE_BUF_LEN;
 267         }
 268         data_ptr[x++] = trace_buf[idx++];
 269     }
 270 }
 271
 272 static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size)
 273 {
 274     uint8_t *data_ptr = dataptr;
 275     uint32_t x = 0;
 276     while (x < size) {
 277         if (idx >= TRACE_BUF_LEN) {
 278             idx = idx % TRACE_BUF_LEN;
 279         }
 280         trace_buf[idx++] = data_ptr[x++];
 281     }
 282     return idx; /* most callers wants to know where to write next */
 283 }
 284
 285 void trace_record_finish(TraceBufferRecord *rec)
 286 {
 287     TraceRecord record;
 288     read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
 289     smp_wmb(); /* write barrier before marking as valid */
 290     record.event |= TRACE_RECORD_VALID;
 291     write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
 292
 293     if (((unsigned int)g_atomic_int_get(&trace_idx) - writeout_idx)
 294         > TRACE_BUF_FLUSH_THRESHOLD) {
 295         flush_trace_file(false);
 296     }
 297 }
 298
 299 void st_set_trace_file_enabled(bool enable)
 300 {
 301     if (enable == !!trace_fp) {
 302         return; /* no change */
 303     }
 304
 305     /* Halt trace writeout */
 306     flush_trace_file(true);
 307     trace_writeout_enabled = false;
 308     flush_trace_file(true);
 309
 310     if (enable) {
 311         static const TraceLogHeader header = {
 312             .header_event_id = HEADER_EVENT_ID,
 313             .header_magic = HEADER_MAGIC,
 314             /* Older log readers will check for version at next location */
 315             .header_version = HEADER_VERSION,
 316         };
 317
 318         trace_fp = fopen(trace_file_name, "wb");
 319         if (!trace_fp) {
 320             return;
 321         }
 322
 323         if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {
 324             fclose(trace_fp);
 325             trace_fp = NULL;
 326             return;
 327         }
 328
 329         /* Resume trace writeout */
 330         trace_writeout_enabled = true;
 331         flush_trace_file(false);
 332     } else {
 333         fclose(trace_fp);
 334         trace_fp = NULL;
 335     }
 336 }
 337
 338 /**
 339  * Set the name of a trace file
 340  *
 341  * @file        The trace file name or NULL for the default name-<pid> set at
 342  *              config time
 343  */
 344 bool st_set_trace_file(const char *file)
 345 {
 346     st_set_trace_file_enabled(false);
 347
 348     g_free(trace_file_name);
 349
 350     if (!file) {
 351         trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, getpid());
 352     } else {
 353         trace_file_name = g_strdup_printf("%s", file);
 354     }
 355
 356     st_set_trace_file_enabled(true);
 357     return true;
 358 }
 359
 360 void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
 361 {
 362     stream_printf(stream, "Trace file \"%s\" %s.\n",
 363                   trace_file_name, trace_fp ? "on" : "off");
 364 }
 365
 366 void st_flush_trace_buffer(void)
 367 {
 368     flush_trace_file(true);
 369 }
 370
 371 /* Helper function to create a thread with signals blocked.  Use glib's
 372  * portable threads since QEMU abstractions cannot be used due to reentrancy in
 373  * the tracer.  Also note the signal masking on POSIX hosts so that the thread
 374  * does not steal signals when the rest of the program wants them blocked.
 375  */
 376 static GThread *trace_thread_create(GThreadFunc fn)
 377 {
 378     GThread *thread;
 379 #ifndef _WIN32
 380     sigset_t set, oldset;
 381
 382     sigfillset(&set);
 383     pthread_sigmask(SIG_SETMASK, &set, &oldset);
 384 #endif
 385
 386 #if GLIB_CHECK_VERSION(2, 31, 0)
 387     thread = g_thread_new("trace-thread", fn, NULL);
 388 #else
 389     thread = g_thread_create(fn, NULL, FALSE, NULL);
 390 #endif
 391
 392 #ifndef _WIN32
 393     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
 394 #endif
 395
 396     return thread;
 397 }
 398
 399 bool st_init(const char *file)
 400 {
 401     GThread *thread;
 402
 403     trace_pid = getpid();
 404
 405 #if !GLIB_CHECK_VERSION(2, 31, 0)
 406     trace_available_cond = g_cond_new();
 407     trace_empty_cond = g_cond_new();
 408 #endif
 409
 410     thread = trace_thread_create(writeout_thread);
 411     if (!thread) {
 412         fprintf(stderr, "warning: unable to initialize simple trace backend\n");
 413         return false;
 414     }
 415
 416     atexit(st_flush_trace_buffer);
 417     st_set_trace_file(file);
 418     return true;
 419 }