Signed-off-by: Markus Armbruster <armbru@redhat.com> Reviewed-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Harsh Prateek Bora <harsh@linux.vnet.ibm.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
435 lines
12 KiB
C
435 lines
12 KiB
C
/*
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* Simple trace backend
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*
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* Copyright IBM, Corp. 2010
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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*/
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#include <stdlib.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <time.h>
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#ifndef _WIN32
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#include <signal.h>
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#include <pthread.h>
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#endif
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#include "qemu/timer.h"
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#include "trace.h"
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#include "trace/control.h"
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/** Trace file header event ID */
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#define HEADER_EVENT_ID (~(uint64_t)0) /* avoids conflicting with TraceEventIDs */
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/** Trace file magic number */
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#define HEADER_MAGIC 0xf2b177cb0aa429b4ULL
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/** Trace file version number, bump if format changes */
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#define HEADER_VERSION 2
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/** Records were dropped event ID */
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#define DROPPED_EVENT_ID (~(uint64_t)0 - 1)
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/** Trace record is valid */
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#define TRACE_RECORD_VALID ((uint64_t)1 << 63)
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/*
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* Trace records are written out by a dedicated thread. The thread waits for
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* records to become available, writes them out, and then waits again.
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*/
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static GStaticMutex trace_lock = G_STATIC_MUTEX_INIT;
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static GCond *trace_available_cond;
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static GCond *trace_empty_cond;
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static bool trace_available;
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static bool trace_writeout_enabled;
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enum {
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TRACE_BUF_LEN = 4096 * 64,
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TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
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};
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uint8_t trace_buf[TRACE_BUF_LEN];
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static unsigned int trace_idx;
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static unsigned int writeout_idx;
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static int dropped_events;
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static FILE *trace_fp;
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static char *trace_file_name;
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/* * Trace buffer entry */
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typedef struct {
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uint64_t event; /* TraceEventID */
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uint64_t timestamp_ns;
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uint32_t length; /* in bytes */
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uint32_t reserved; /* unused */
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uint64_t arguments[];
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} TraceRecord;
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typedef struct {
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uint64_t header_event_id; /* HEADER_EVENT_ID */
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uint64_t header_magic; /* HEADER_MAGIC */
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uint64_t header_version; /* HEADER_VERSION */
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} TraceLogHeader;
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static void read_from_buffer(unsigned int idx, void *dataptr, size_t size);
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static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size);
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static void clear_buffer_range(unsigned int idx, size_t len)
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{
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uint32_t num = 0;
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while (num < len) {
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if (idx >= TRACE_BUF_LEN) {
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idx = idx % TRACE_BUF_LEN;
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}
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trace_buf[idx++] = 0;
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num++;
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}
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}
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/**
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* Read a trace record from the trace buffer
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*
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* @idx Trace buffer index
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* @record Trace record to fill
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*
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* Returns false if the record is not valid.
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*/
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static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)
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{
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uint64_t event_flag = 0;
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TraceRecord record;
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/* read the event flag to see if its a valid record */
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read_from_buffer(idx, &record, sizeof(event_flag));
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if (!(record.event & TRACE_RECORD_VALID)) {
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return false;
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}
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smp_rmb(); /* read memory barrier before accessing record */
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/* read the record header to know record length */
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read_from_buffer(idx, &record, sizeof(TraceRecord));
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*recordptr = malloc(record.length); /* dont use g_malloc, can deadlock when traced */
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/* make a copy of record to avoid being overwritten */
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read_from_buffer(idx, *recordptr, record.length);
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smp_rmb(); /* memory barrier before clearing valid flag */
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(*recordptr)->event &= ~TRACE_RECORD_VALID;
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/* clear the trace buffer range for consumed record otherwise any byte
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* with its MSB set may be considered as a valid event id when the writer
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* thread crosses this range of buffer again.
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*/
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clear_buffer_range(idx, record.length);
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return true;
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}
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/**
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* Kick writeout thread
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*
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* @wait Whether to wait for writeout thread to complete
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*/
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static void flush_trace_file(bool wait)
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{
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g_static_mutex_lock(&trace_lock);
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trace_available = true;
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g_cond_signal(trace_available_cond);
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if (wait) {
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g_cond_wait(trace_empty_cond, g_static_mutex_get_mutex(&trace_lock));
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}
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g_static_mutex_unlock(&trace_lock);
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}
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static void wait_for_trace_records_available(void)
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{
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g_static_mutex_lock(&trace_lock);
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while (!(trace_available && trace_writeout_enabled)) {
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g_cond_signal(trace_empty_cond);
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g_cond_wait(trace_available_cond,
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g_static_mutex_get_mutex(&trace_lock));
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}
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trace_available = false;
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g_static_mutex_unlock(&trace_lock);
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}
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static gpointer writeout_thread(gpointer opaque)
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{
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TraceRecord *recordptr;
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union {
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TraceRecord rec;
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uint8_t bytes[sizeof(TraceRecord) + sizeof(uint64_t)];
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} dropped;
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unsigned int idx = 0;
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int dropped_count;
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size_t unused __attribute__ ((unused));
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for (;;) {
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wait_for_trace_records_available();
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if (g_atomic_int_get(&dropped_events)) {
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dropped.rec.event = DROPPED_EVENT_ID,
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dropped.rec.timestamp_ns = get_clock();
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dropped.rec.length = sizeof(TraceRecord) + sizeof(uint64_t),
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dropped.rec.reserved = 0;
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do {
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dropped_count = g_atomic_int_get(&dropped_events);
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} while (!g_atomic_int_compare_and_exchange(&dropped_events,
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dropped_count, 0));
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dropped.rec.arguments[0] = dropped_count;
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unused = fwrite(&dropped.rec, dropped.rec.length, 1, trace_fp);
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}
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while (get_trace_record(idx, &recordptr)) {
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unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
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writeout_idx += recordptr->length;
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free(recordptr); /* dont use g_free, can deadlock when traced */
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idx = writeout_idx % TRACE_BUF_LEN;
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}
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fflush(trace_fp);
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}
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return NULL;
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}
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void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)
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{
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rec->rec_off = write_to_buffer(rec->rec_off, &val, sizeof(uint64_t));
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}
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void trace_record_write_str(TraceBufferRecord *rec, const char *s, uint32_t slen)
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{
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/* Write string length first */
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rec->rec_off = write_to_buffer(rec->rec_off, &slen, sizeof(slen));
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/* Write actual string now */
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rec->rec_off = write_to_buffer(rec->rec_off, (void*)s, slen);
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}
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int trace_record_start(TraceBufferRecord *rec, TraceEventID event, size_t datasize)
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{
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unsigned int idx, rec_off, old_idx, new_idx;
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uint32_t rec_len = sizeof(TraceRecord) + datasize;
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uint64_t timestamp_ns = get_clock();
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do {
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old_idx = g_atomic_int_get(&trace_idx);
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smp_rmb();
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new_idx = old_idx + rec_len;
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if (new_idx - writeout_idx > TRACE_BUF_LEN) {
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/* Trace Buffer Full, Event dropped ! */
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g_atomic_int_inc(&dropped_events);
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return -ENOSPC;
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}
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} while (!g_atomic_int_compare_and_exchange(&trace_idx, old_idx, new_idx));
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idx = old_idx % TRACE_BUF_LEN;
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rec_off = idx;
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rec_off = write_to_buffer(rec_off, &event, sizeof(event));
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rec_off = write_to_buffer(rec_off, ×tamp_ns, sizeof(timestamp_ns));
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rec_off = write_to_buffer(rec_off, &rec_len, sizeof(rec_len));
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rec->tbuf_idx = idx;
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rec->rec_off = (idx + sizeof(TraceRecord)) % TRACE_BUF_LEN;
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return 0;
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}
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static void read_from_buffer(unsigned int idx, void *dataptr, size_t size)
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{
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uint8_t *data_ptr = dataptr;
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uint32_t x = 0;
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while (x < size) {
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if (idx >= TRACE_BUF_LEN) {
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idx = idx % TRACE_BUF_LEN;
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}
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data_ptr[x++] = trace_buf[idx++];
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}
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}
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static unsigned int write_to_buffer(unsigned int idx, void *dataptr, size_t size)
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{
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uint8_t *data_ptr = dataptr;
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uint32_t x = 0;
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while (x < size) {
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if (idx >= TRACE_BUF_LEN) {
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idx = idx % TRACE_BUF_LEN;
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}
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trace_buf[idx++] = data_ptr[x++];
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}
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return idx; /* most callers wants to know where to write next */
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}
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void trace_record_finish(TraceBufferRecord *rec)
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{
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TraceRecord record;
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read_from_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
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smp_wmb(); /* write barrier before marking as valid */
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record.event |= TRACE_RECORD_VALID;
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write_to_buffer(rec->tbuf_idx, &record, sizeof(TraceRecord));
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if ((g_atomic_int_get(&trace_idx) - writeout_idx)
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> TRACE_BUF_FLUSH_THRESHOLD) {
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flush_trace_file(false);
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}
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}
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void st_set_trace_file_enabled(bool enable)
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{
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if (enable == !!trace_fp) {
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return; /* no change */
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}
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/* Halt trace writeout */
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flush_trace_file(true);
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trace_writeout_enabled = false;
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flush_trace_file(true);
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if (enable) {
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static const TraceLogHeader header = {
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.header_event_id = HEADER_EVENT_ID,
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.header_magic = HEADER_MAGIC,
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/* Older log readers will check for version at next location */
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.header_version = HEADER_VERSION,
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};
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trace_fp = fopen(trace_file_name, "wb");
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if (!trace_fp) {
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return;
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}
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if (fwrite(&header, sizeof header, 1, trace_fp) != 1) {
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fclose(trace_fp);
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trace_fp = NULL;
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return;
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}
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/* Resume trace writeout */
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trace_writeout_enabled = true;
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flush_trace_file(false);
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} else {
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fclose(trace_fp);
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trace_fp = NULL;
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}
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}
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/**
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* Set the name of a trace file
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*
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* @file The trace file name or NULL for the default name-<pid> set at
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* config time
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*/
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bool st_set_trace_file(const char *file)
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{
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st_set_trace_file_enabled(false);
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g_free(trace_file_name);
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if (!file) {
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trace_file_name = g_strdup_printf(CONFIG_TRACE_FILE, getpid());
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} else {
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trace_file_name = g_strdup_printf("%s", file);
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}
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st_set_trace_file_enabled(true);
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return true;
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}
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void st_print_trace_file_status(FILE *stream, int (*stream_printf)(FILE *stream, const char *fmt, ...))
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{
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stream_printf(stream, "Trace file \"%s\" %s.\n",
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trace_file_name, trace_fp ? "on" : "off");
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}
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void st_flush_trace_buffer(void)
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{
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flush_trace_file(true);
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}
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void trace_print_events(FILE *stream, fprintf_function stream_printf)
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{
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unsigned int i;
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for (i = 0; i < NR_TRACE_EVENTS; i++) {
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stream_printf(stream, "%s [Event ID %u] : state %u\n",
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trace_list[i].tp_name, i, trace_list[i].state);
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}
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}
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bool trace_event_set_state(const char *name, bool state)
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{
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unsigned int i;
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unsigned int len;
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bool wildcard = false;
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bool matched = false;
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len = strlen(name);
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if (len > 0 && name[len - 1] == '*') {
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wildcard = true;
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len -= 1;
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}
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for (i = 0; i < NR_TRACE_EVENTS; i++) {
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if (wildcard) {
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if (!strncmp(trace_list[i].tp_name, name, len)) {
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trace_list[i].state = state;
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matched = true;
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}
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continue;
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}
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if (!strcmp(trace_list[i].tp_name, name)) {
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trace_list[i].state = state;
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return true;
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}
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}
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return matched;
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}
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/* Helper function to create a thread with signals blocked. Use glib's
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* portable threads since QEMU abstractions cannot be used due to reentrancy in
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* the tracer. Also note the signal masking on POSIX hosts so that the thread
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* does not steal signals when the rest of the program wants them blocked.
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*/
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static GThread *trace_thread_create(GThreadFunc fn)
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{
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GThread *thread;
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#ifndef _WIN32
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sigset_t set, oldset;
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sigfillset(&set);
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pthread_sigmask(SIG_SETMASK, &set, &oldset);
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#endif
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thread = g_thread_create(fn, NULL, FALSE, NULL);
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#ifndef _WIN32
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pthread_sigmask(SIG_SETMASK, &oldset, NULL);
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#endif
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return thread;
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}
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bool trace_backend_init(const char *events, const char *file)
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{
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GThread *thread;
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if (!g_thread_supported()) {
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#if !GLIB_CHECK_VERSION(2, 31, 0)
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g_thread_init(NULL);
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#else
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fprintf(stderr, "glib threading failed to initialize.\n");
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exit(1);
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#endif
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}
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trace_available_cond = g_cond_new();
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trace_empty_cond = g_cond_new();
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thread = trace_thread_create(writeout_thread);
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if (!thread) {
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fprintf(stderr, "warning: unable to initialize simple trace backend\n");
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return false;
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}
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atexit(st_flush_trace_buffer);
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trace_backend_init_events(events);
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st_set_trace_file(file);
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return true;
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}
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