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); /* dont 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); /* dont 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 }