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ringbuf: add zero-copy reader callback API #1930

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ringbuf: add zero-copy reader callback API #1930

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18 changes: 16 additions & 2 deletions ringbuf/reader.go
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Original file line number Diff line number Diff line change
Expand Up @@ -135,7 +135,7 @@ func (r *Reader) SetDeadline(t time.Time) {
// Returns [os.ErrDeadlineExceeded] if a deadline was set and after all records
// have been read from the ring.
//
// See [ReadInto] for a more efficient version of this method.
// See [ReadInto] or [ReadZeroCopy] for more efficient versions of this method.
func (r *Reader) Read() (Record, error) {
var rec Record
err := r.ReadInto(&rec)
Expand All @@ -144,6 +144,20 @@ func (r *Reader) Read() (Record, error) {

// ReadInto is like Read except that it allows reusing Record and associated buffers.
func (r *Reader) ReadInto(rec *Record) error {
return r.readLockedPoll(func() error {
return r.ring.readRecord(rec)
})
}

// ReadZeroCopy reads the next record from the BPF ringbuf using a zero-copy callback.
// The sample slice is only valid until the callback returns.
func (r *Reader) ReadZeroCopy(f func(sample []byte, remaining int) error) error {
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@florianl florianl Jan 16, 2026

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Following the code, I think this function has the potential be used incorrectly?

var saved []byte
reader.ReadZeroCopy(func(sample []byte, remaining int) error {
    saved = sample  // retains reference to temporary memory?
    return nil
})
// is saved still valid at this point?

return r.readLockedPoll(func() error {
return r.ring.readRecordZeroCopy(f)
})
}

func (r *Reader) readLockedPoll(read func() error) error {
r.mu.Lock()
defer r.mu.Unlock()

Expand Down Expand Up @@ -171,7 +185,7 @@ func (r *Reader) ReadInto(rec *Record) error {
}

for {
err := r.ring.readRecord(rec)
err := read()
// Not using errors.Is which is quite a bit slower
// For a tight loop it might make a difference
if err == errBusy {
Expand Down
27 changes: 18 additions & 9 deletions ringbuf/ring.go
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Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,21 @@ func (rr *ringReader) AvailableBytes() uint64 {

// Read a record from an event ring.
func (rr *ringReader) readRecord(rec *Record) error {
return rr.readRecordZeroCopy(func(sample []byte, remaining int) error {
n := len(sample)
if cap(rec.RawSample) < n {
rec.RawSample = make([]byte, n)
} else {
rec.RawSample = rec.RawSample[:n]
}
copy(rec.RawSample, sample)
rec.Remaining = remaining

return nil
})
}

func (rr *ringReader) readRecordZeroCopy(f func(sample []byte, remaining int) error) error {
prod := atomic.LoadUintptr(rr.prod_pos)
cons := atomic.LoadUintptr(rr.cons_pos)

Expand Down Expand Up @@ -87,15 +102,9 @@ func (rr *ringReader) readRecord(rec *Record) error {
continue
}

if n := header.dataLen(); cap(rec.RawSample) < n {
rec.RawSample = make([]byte, n)
} else {
rec.RawSample = rec.RawSample[:n]
}

copy(rec.RawSample, rr.ring[start:])
rec.Remaining = int(prod - cons)
n := header.dataLen()
err := f(rr.ring[start:start+uintptr(n)], int(prod-cons))
atomic.StoreUintptr(rr.cons_pos, cons)
return nil
return err
}
}