[Qemu-devel] [PATCH 2/3] simpletrace v2: Support var number of args, strings.

[Harsh Prateek Bora]

A newer tracelog format which gets rid of fixed size trace records and
therefore allows to trace multiple arguments as well as strings in trace
events.

Sample trace:
v9fs_version 0.000 tag=0xffff id=0x64 msize=0x2000 version=9P2000.L
v9fs_version_return 6.705 tag=0xffff id=0x64 msize=0x2000 version=9P2000.L
v9fs_attach 174.467 tag=0x1 id=0x68 fid=0x0 afid=0xffffffffffffffff 
uname=nobody aname=
v9fs_attach_return 4720.454 tag=0x1 id=0x68 type=0xffffffffffffff80 
version=0x4f2a4dd0  path=0x220ea6

Signed-off-by: Harsh Prateek Bora <address@hidden>
---
 scripts/tracetool/backend/simple.py |   84 +++++++++---
 trace/simple.c                      |  246 ++++++++++++++++++++---------------
 trace/simple.h                      |   39 +++++-
 3 files changed, 240 insertions(+), 129 deletions(-)

diff --git a/scripts/tracetool/backend/simple.py 
b/scripts/tracetool/backend/simple.py
index fbb5717..ef9ed93 100644
--- a/scripts/tracetool/backend/simple.py
+++ b/scripts/tracetool/backend/simple.py
@@ -15,9 +15,16 @@ __email__      = "address@hidden"
 
 from tracetool import out
 
+def is_string(arg):
+    strtype = ('const char*', 'char*', 'const char *', 'char *')
+    if arg.lstrip().startswith(strtype):
+        return True
+    else:
+        return False
 
 def c(events):
     out('#include "trace.h"',
+        '#include "trace/simple.h"',
         '',
         'TraceEvent trace_list[] = {')
 
@@ -26,30 +33,69 @@ def c(events):
             name = e.name,
             )
 
-    out('};')
-
-def h(events):
-    out('#include "trace/simple.h"',
+    out('};',
         '')
 
-    for num, e in enumerate(events):
-        if len(e.args):
-            argstr = e.args.names()
-            arg_prefix = ', (uint64_t)(uintptr_t)'
-            cast_args = arg_prefix + arg_prefix.join(argstr)
-            simple_args = (str(num) + cast_args)
-        else:
-            simple_args = str(num)
+    for num, event in enumerate(events):
+        sizes = []
+        for type_, name in event.args:
+            if is_string(type_):
+                sizes.append("4 + safe_strlen(%s)" % name)
+            else:
+                sizes.append("8")
+        sizestr = " + ".join(sizes)
+        if len(event.args) == 0:
+            sizestr = '0'
 
-        out('static inline void trace_%(name)s(%(args)s)',
+        out('void trace_%(name)s(%(args)s)',
             '{',
-            '    trace%(argc)d(%(trace_args)s);',
-            '}',
-            name = e.name,
-            args = e.args,
-            argc = len(e.args),
-            trace_args = simple_args,
+            '    TraceBufferRecord rec;',
+            '',
+            '    if (!trace_list[%(event_id)s].state) {',
+            '        return;',
+            '    }',
+            '',
+            '    if (trace_record_start(&rec, %(event_id)s, %(size_str)s)) {',
+            '        return; /* Trace Buffer Full, Event Dropped ! */',
+            '    }',
+            name = event.name,
+            args = event.args,
+            event_id = num,
+            size_str = sizestr,
             )
 
+        if len(event.args) > 0:
+            for type_, name in event.args:
+                # string
+                if is_string(type_):
+                    out('    trace_record_write_str(&rec, %(name)s);',
+                        name = name,
+                       )
+                # pointer var (not string)
+                elif type_.endswith('*'):
+                    out('    trace_record_write_u64(&rec, (uint64_t)(uint64_t 
*)%(name)s);',
+                        name = name,
+                       )
+                # primitive data type
+                else:
+                    out('    trace_record_write_u64(&rec, 
(uint64_t)%(name)s);',
+                       name = name,
+                       )
+
+        out('    trace_record_finish(&rec);',
+            '}',
+            '')
+
+
+def h(events):
+    out('#include "trace/simple.h"',
+        '')
+
+    for event in events:
+        out('void trace_%(name)s(%(args)s);',
+            name = event.name,
+            args = event.args,
+            )
+    out('')
     out('#define NR_TRACE_EVENTS %d' % len(events))
     out('extern TraceEvent trace_list[NR_TRACE_EVENTS];')
diff --git a/trace/simple.c b/trace/simple.c
index 33ae486..6b18f8b 100644
--- a/trace/simple.c
+++ b/trace/simple.c
@@ -27,7 +27,7 @@
 #define HEADER_MAGIC 0xf2b177cb0aa429b4ULL
 
 /** Trace file version number, bump if format changes */
-#define HEADER_VERSION 0
+#define HEADER_VERSION 2
 
 /** Records were dropped event ID */
 #define DROPPED_EVENT_ID (~(uint64_t)0 - 1)
@@ -35,23 +35,6 @@
 /** Trace record is valid */
 #define TRACE_RECORD_VALID ((uint64_t)1 << 63)
 
-/** Trace buffer entry */
-typedef struct {
-    uint64_t event;
-    uint64_t timestamp_ns;
-    uint64_t x1;
-    uint64_t x2;
-    uint64_t x3;
-    uint64_t x4;
-    uint64_t x5;
-    uint64_t x6;
-} TraceRecord;
-
-enum {
-    TRACE_BUF_LEN = 4096,
-    TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
-};
-
 /*
  * Trace records are written out by a dedicated thread.  The thread waits for
  * records to become available, writes them out, and then waits again.
@@ -62,11 +45,49 @@ static GCond *trace_empty_cond;
 static bool trace_available;
 static bool trace_writeout_enabled;
 
-static TraceRecord trace_buf[TRACE_BUF_LEN];
+enum {
+    TRACE_BUF_LEN = 4096 * 64,
+    TRACE_BUF_FLUSH_THRESHOLD = TRACE_BUF_LEN / 4,
+};
+
+uint8_t trace_buf[TRACE_BUF_LEN];
 static unsigned int trace_idx;
+static unsigned int writeout_idx;
+static uint64_t dropped_events;
 static FILE *trace_fp;
 static char *trace_file_name = NULL;
 
+/* * Trace buffer entry */
+typedef struct {
+    uint64_t event; /*   TraceEventID */
+    uint64_t timestamp_ns;
+    uint32_t length;   /*    in bytes */
+    uint32_t reserved; /*    unused */
+    uint8_t arguments[]; /*  arguments position affects ST_REC_HDR_LEN */
+} TraceRecord;
+
+typedef struct {
+    uint64_t header_event_id; /* HEADER_EVENT_ID */
+    uint64_t header_magic;    /* HEADER_MAGIC    */
+    uint64_t header_version;  /* HEADER_VERSION  */
+} TraceRecordHeader;
+
+/* * Trace record header length */
+#define ST_REC_HDR_LEN 24
+
+int trace_alloc_record(TraceBufferRecord *rec, TraceEventID event, uint32_t 
datasize);
+static void read_from_buffer(unsigned int idx, uint8_t *dataptr, uint32_t 
size);
+static void write_to_buffer(unsigned int idx, uint8_t *dataptr, uint32_t size);
+void trace_mark_record_complete(TraceBufferRecord *rec);
+
+uint32_t safe_strlen(const char* str)
+{
+    if (str == NULL) {
+        return 0;
+    }
+    return strlen(str);
+}
+
 /**
  * Read a trace record from the trace buffer
  *
@@ -75,16 +96,22 @@ static char *trace_file_name = NULL;
  *
  * Returns false if the record is not valid.
  */
-static bool get_trace_record(unsigned int idx, TraceRecord *record)
+static bool get_trace_record(unsigned int idx, TraceRecord **recordptr)
 {
-    if (!(trace_buf[idx].event & TRACE_RECORD_VALID)) {
+    uint8_t temp_rec[ST_REC_HDR_LEN];
+    TraceRecord *record = (TraceRecord *) temp_rec;
+    read_from_buffer(idx, temp_rec, ST_REC_HDR_LEN);
+
+    if (!(record->event & TRACE_RECORD_VALID)) {
         return false;
     }
 
     __sync_synchronize(); /* read memory barrier before accessing record */
 
-    *record = trace_buf[idx];
-    record->event &= ~TRACE_RECORD_VALID;
+    *recordptr = g_malloc(record->length);
+    /* make a copy of record to avoid being overwritten */
+    read_from_buffer(idx, (uint8_t *)*recordptr, record->length);
+    (*recordptr)->event &= ~TRACE_RECORD_VALID;
     return true;
 }
 
@@ -120,29 +147,31 @@ static void wait_for_trace_records_available(void)
 
 static gpointer writeout_thread(gpointer opaque)
 {
-    TraceRecord record;
-    unsigned int writeout_idx = 0;
-    unsigned int num_available, idx;
+    TraceRecord *recordptr;
+    unsigned int idx = 0;
     size_t unused __attribute__ ((unused));
 
     for (;;) {
         wait_for_trace_records_available();
 
-        num_available = trace_idx - writeout_idx;
-        if (num_available > TRACE_BUF_LEN) {
-            record = (TraceRecord){
-                .event = DROPPED_EVENT_ID,
-                .x1 = num_available,
-            };
-            unused = fwrite(&record, sizeof(record), 1, trace_fp);
-            writeout_idx += num_available;
+        if (dropped_events) {
+            recordptr = g_malloc(ST_REC_HDR_LEN + sizeof(dropped_events));
+            recordptr->event = DROPPED_EVENT_ID,
+            recordptr->timestamp_ns = get_clock();
+            recordptr->length = ST_REC_HDR_LEN + sizeof(dropped_events),
+            recordptr->reserved = 0;
+            *(uint64_t *) &(recordptr->arguments[0]) = dropped_events;
+            dropped_events = 0;
+            unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
         }
 
-        idx = writeout_idx % TRACE_BUF_LEN;
-        while (get_trace_record(idx, &record)) {
-            trace_buf[idx].event = 0; /* clear valid bit */
-            unused = fwrite(&record, sizeof(record), 1, trace_fp);
-            idx = ++writeout_idx % TRACE_BUF_LEN;
+        while (get_trace_record(idx, &recordptr)) {
+            unused = fwrite(recordptr, recordptr->length, 1, trace_fp);
+            writeout_idx += recordptr->length;
+            g_free(recordptr);
+            recordptr = (TraceRecord *) &trace_buf[idx];
+            recordptr->event = 0;
+            idx = writeout_idx % TRACE_BUF_LEN;
         }
 
         fflush(trace_fp);
@@ -150,72 +179,101 @@ static gpointer writeout_thread(gpointer opaque)
     return NULL;
 }
 
-static void trace(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3,
-                  uint64_t x4, uint64_t x5, uint64_t x6)
+int trace_record_start(TraceBufferRecord *rec, TraceEventID id, size_t arglen)
 {
-    unsigned int idx;
-    uint64_t timestamp;
-
-    if (!trace_list[event].state) {
-        return;
-    }
-
-    timestamp = get_clock();
-
-    idx = g_atomic_int_exchange_and_add((gint *)&trace_idx, 1) % TRACE_BUF_LEN;
-    trace_buf[idx] = (TraceRecord){
-        .event = event,
-        .timestamp_ns = timestamp,
-        .x1 = x1,
-        .x2 = x2,
-        .x3 = x3,
-        .x4 = x4,
-        .x5 = x5,
-        .x6 = x6,
-    };
-    __sync_synchronize(); /* write barrier before marking as valid */
-    trace_buf[idx].event |= TRACE_RECORD_VALID;
-
-    if ((idx + 1) % TRACE_BUF_FLUSH_THRESHOLD == 0) {
-        flush_trace_file(false);
-    }
+    return trace_alloc_record(rec, id, arglen); /* return 0 on success */
 }
 
-void trace0(TraceEventID event)
+void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val)
 {
-    trace(event, 0, 0, 0, 0, 0, 0);
+    write_to_buffer(rec->rec_off, (uint8_t *)&val, sizeof(uint64_t));
+    rec->rec_off += sizeof(uint64_t);
 }
 
-void trace1(TraceEventID event, uint64_t x1)
+void trace_record_write_str(TraceBufferRecord *rec, const char *s)
 {
-    trace(event, x1, 0, 0, 0, 0, 0);
+    /* Write string length first */
+    uint32_t slen = (s == NULL ? 0 : strlen(s));
+    write_to_buffer(rec->rec_off, (uint8_t *)&slen, sizeof(slen));
+    rec->rec_off += sizeof(slen);
+    /* Write actual string now */
+    write_to_buffer(rec->rec_off, (uint8_t *)s, slen);
+    rec->rec_off += slen;
 }
 
-void trace2(TraceEventID event, uint64_t x1, uint64_t x2)
+void trace_record_finish(TraceBufferRecord *rec)
 {
-    trace(event, x1, x2, 0, 0, 0, 0);
+    trace_mark_record_complete(rec);
 }
 
-void trace3(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3)
+int trace_alloc_record(TraceBufferRecord *rec, TraceEventID event, uint32_t 
datasize)
 {
-    trace(event, x1, x2, x3, 0, 0, 0);
+    unsigned int idx, rec_off;
+    uint32_t rec_len = ST_REC_HDR_LEN + datasize;
+    uint64_t timestamp_ns = get_clock();
+
+    if ((rec_len + trace_idx - writeout_idx) > TRACE_BUF_LEN) {
+        /* Trace Buffer Full, Event dropped ! */
+        dropped_events++;
+        return 1;
+    }
+    idx = g_atomic_int_exchange_and_add((gint *)&trace_idx, rec_len) % 
TRACE_BUF_LEN;
+
+    /*  To check later if threshold crossed */
+    rec->next_tbuf_idx = trace_idx % TRACE_BUF_LEN;
+
+    rec_off = idx;
+    write_to_buffer(rec_off, (uint8_t*)&event, sizeof(event));
+    rec_off += sizeof(event);
+    write_to_buffer(rec_off, (uint8_t*)&timestamp_ns, sizeof(timestamp_ns));
+    rec_off += sizeof(timestamp_ns);
+    write_to_buffer(rec_off, (uint8_t*)&rec_len, sizeof(rec_len));
+    rec_off += sizeof(rec_len);
+
+    rec->tbuf_idx = idx;
+    rec->rec_off  = (idx + ST_REC_HDR_LEN) % TRACE_BUF_LEN;
+    return 0;
 }
 
-void trace4(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, 
uint64_t x4)
+static void read_from_buffer(unsigned int idx, uint8_t *dataptr, uint32_t size)
 {
-    trace(event, x1, x2, x3, x4, 0, 0);
+    uint32_t x = 0;
+    while (x < size) {
+        if (idx >= TRACE_BUF_LEN) {
+            idx = idx % TRACE_BUF_LEN;
+        }
+        dataptr[x++] = trace_buf[idx++];
+    }
 }
 
-void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, 
uint64_t x4, uint64_t x5)
+static void write_to_buffer(unsigned int idx, uint8_t *dataptr, uint32_t size)
 {
-    trace(event, x1, x2, x3, x4, x5, 0);
+    uint32_t x = 0;
+    while (x < size) {
+        if (idx >= TRACE_BUF_LEN) {
+            idx = idx % TRACE_BUF_LEN;
+        }
+        trace_buf[idx++] = dataptr[x++];
+    }
 }
 
-void trace6(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, 
uint64_t x4, uint64_t x5, uint64_t x6)
+void trace_mark_record_complete(TraceBufferRecord *rec)
 {
-    trace(event, x1, x2, x3, x4, x5, x6);
+    uint8_t temp_rec[ST_REC_HDR_LEN];
+    TraceRecord *record = (TraceRecord *) temp_rec;
+    read_from_buffer(rec->tbuf_idx, temp_rec, ST_REC_HDR_LEN);
+    __sync_synchronize(); /* write barrier before marking as valid */
+    record->event |= TRACE_RECORD_VALID;
+    write_to_buffer(rec->tbuf_idx, temp_rec, ST_REC_HDR_LEN);
+
+    if (rec->next_tbuf_idx > TRACE_BUF_FLUSH_THRESHOLD &&
+        rec->tbuf_idx <= TRACE_BUF_FLUSH_THRESHOLD) {
+        flush_trace_file(false);
+    }
 }
 
+
+
 void st_set_trace_file_enabled(bool enable)
 {
     if (enable == !!trace_fp) {
@@ -228,10 +286,11 @@ void st_set_trace_file_enabled(bool enable)
     flush_trace_file(true);
 
     if (enable) {
-        static const TraceRecord header = {
-            .event = HEADER_EVENT_ID,
-            .timestamp_ns = HEADER_MAGIC,
-            .x1 = HEADER_VERSION,
+        static const TraceRecordHeader header = {
+            .header_event_id = HEADER_EVENT_ID,
+            .header_magic = HEADER_MAGIC,
+            /* Older log readers will check for version at next location */
+            .header_version = HEADER_VERSION,
         };
 
         trace_fp = fopen(trace_file_name, "wb");
@@ -288,23 +347,6 @@ void st_print_trace_file_status(FILE *stream, int 
(*stream_printf)(FILE *stream,
                   trace_file_name, trace_fp ? "on" : "off");
 }
 
-void st_print_trace(FILE *stream, int (*stream_printf)(FILE *stream, const 
char *fmt, ...))
-{
-    unsigned int i;
-
-    for (i = 0; i < TRACE_BUF_LEN; i++) {
-        TraceRecord record;
-
-        if (!get_trace_record(i, &record)) {
-            continue;
-        }
-        stream_printf(stream, "Event %" PRIu64 " : %" PRIx64 " %" PRIx64
-                      " %" PRIx64 " %" PRIx64 " %" PRIx64 " %" PRIx64 "\n",
-                      record.event, record.x1, record.x2,
-                      record.x3, record.x4, record.x5,
-                      record.x6);
-    }
-}
 
 void st_flush_trace_buffer(void)
 {
diff --git a/trace/simple.h b/trace/simple.h
index 466e75b..30f926a 100644
--- a/trace/simple.h
+++ b/trace/simple.h
@@ -22,17 +22,40 @@ typedef struct {
     bool state;
 } TraceEvent;
 
-void trace0(TraceEventID event);
-void trace1(TraceEventID event, uint64_t x1);
-void trace2(TraceEventID event, uint64_t x1, uint64_t x2);
-void trace3(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3);
-void trace4(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, 
uint64_t x4);
-void trace5(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, 
uint64_t x4, uint64_t x5);
-void trace6(TraceEventID event, uint64_t x1, uint64_t x2, uint64_t x3, 
uint64_t x4, uint64_t x5, uint64_t x6);
-void st_print_trace(FILE *stream, fprintf_function stream_printf);
 void st_print_trace_file_status(FILE *stream, fprintf_function stream_printf);
 void st_set_trace_file_enabled(bool enable);
 bool st_set_trace_file(const char *file);
 void st_flush_trace_buffer(void);
 
+typedef struct {
+    unsigned int tbuf_idx;
+    unsigned int next_tbuf_idx;
+    unsigned int rec_off;
+} TraceBufferRecord;
+
+/**
+ * Initialize a trace record and claim space for it in the buffer
+ *
+ * @arglen  number of bytes required for arguments
+ */
+int trace_record_start(TraceBufferRecord *rec, TraceEventID id, size_t arglen);
+
+/**
+ * Append a 64-bit argument to a trace record
+ */
+void trace_record_write_u64(TraceBufferRecord *rec, uint64_t val);
+
+/**
+ * Append a string argument to a trace record
+ */
+void trace_record_write_str(TraceBufferRecord *rec, const char *s);
+
+/**
+ * Mark a trace record completed
+ *
+ * Don't append any more arguments to the trace record after calling this.
+ */
+void trace_record_finish(TraceBufferRecord *rec);
+uint32_t safe_strlen(const char* str);
+
 #endif /* TRACE_SIMPLE_H */
-- 
1.7.1.1