Add Remaining and Size to perf/ring Record

Signed-off-by: Bryce Kahle <bryce.kahle@datadoghq.com>

perf/reader.go

@@ -48,6 +48,12 @@ type Record struct {
 	// The number of samples which could not be output, since
 	// the ring buffer was full.
 	LostSamples uint64
+
+	// The number of bytes remaining in the per-CPU perf buffer after this Record has been read.
+	Remaining int
+
+	// The total size of the per-CPU perf buffer in bytes.
+	Size int
 }
 
 // Read a record from a reader and tag it as being from the given CPU.
@@ -439,6 +445,8 @@ func (pr *Reader) readRecordFromRing(rec *Record, ring *perfEventRing) error {
 	if pr.overwritable && (errors.Is(err, io.EOF) || errors.Is(err, io.ErrUnexpectedEOF)) {
 		return errEOR
 	}
+	rec.Size = ring.size()
+	rec.Remaining = ring.remaining()
 	return err
 }
 

perf/ring.go

@@ -127,6 +127,7 @@ func createPerfEvent(cpu, watermark int, overwritable bool) (int, error) {
 type ringReader interface {
 	loadHead()
 	size() int
+	remaining() int
 	writeTail()
 	Read(p []byte) (int, error)
 }
@@ -157,6 +158,10 @@ func (rr *forwardReader) size() int {
 	return len(rr.ring)
 }
 
+func (rr *forwardReader) remaining() int {
+	return int((rr.head - rr.tail) & rr.mask)
+}
+
 func (rr *forwardReader) writeTail() {
 	// Commit the new tail. This lets the kernel know that
 	// the ring buffer has been consumed.
@@ -244,6 +249,10 @@ func (rr *reverseReader) size() int {
 	return len(rr.ring)
 }
 
+func (rr *reverseReader) remaining() int {
+	return int((rr.tail - rr.read) & rr.mask)
+}
+
 func (rr *reverseReader) writeTail() {
 	// We do not care about tail for over writable perf buffer.
 	// So, this function is noop.

ringbuf/reader.go

@@ -44,6 +44,12 @@ func (rh *ringbufHeader) dataLen() int {
 
 type Record struct {
 	RawSample []byte
+
+	// The number of bytes remaining in the ring buffer after this Record has been read.
+	Remaining int
+
+	// The total size of the ring buffer in bytes.
+	Size int
 }
 
 // Read a record from an event ring.
@@ -98,6 +104,8 @@ func readRecord(rd *ringbufEventRing, rec *Record, buf []byte) error {
 
 	rd.storeConsumer()
 	rec.RawSample = rec.RawSample[:header.dataLen()]
+	rec.Size = rd.size()
+	rec.Remaining = rd.remaining()
 	return nil
 }
 

ringbuf/ring.go

@@ -98,6 +98,17 @@ func (rr *ringReader) isEmpty() bool {
 	return prod == cons
 }
 
+func (rr *ringReader) size() int {
+	return cap(rr.ring)
+}
+
+func (rr *ringReader) remaining() int {
+	cons := atomic.LoadUint64(rr.cons_pos)
+	prod := atomic.LoadUint64(rr.prod_pos)
+
+	return int((prod - cons) & rr.mask)
+}
+
 func (rr *ringReader) Read(p []byte) (int, error) {
 	prod := atomic.LoadUint64(rr.prod_pos)