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