Re: [Libguestfs] [PATCH libnbd 5/9] golang: aio_buffer.go: Add Slice()

AioBuffer.Bytes() cannot be used for coping images from NBD to other

APis because it copies the entire image. Add a new Slice() function, creating a slice backed by the underling buffer.

Using Slice() is efficient, but less safe, like Get(). The returned slice must be used only before calling Free(). This should not be an issue with typical code. Testing show that Slice() is much faster than Bytes() for typical 256k buffer: BenchmarkAioBufferBytes-12 86616 16529 ns/op BenchmarkAioBufferSlice-12 1000000000 0.4630 ns/op I modified the aio_copy example to use AioBuffer and complied 2

+++ b/golang/libnbd_620_aio_buffer_test.go @@ -44,20 +44,35 @@ func TestAioBuffer(t *testing.T) { /* Modifying returned slice does not modify the buffer. */ for i := 0; i < len(b); i++ { b[i] = 42 } /* Bytes() still returns zeroes. */ if !bytes.Equal(buf.Bytes(), zeroes) { t.Fatalf("Expected %v, got %v", zeroes, buf.Bytes()) } + /* Creating a slice without copying the underlhing buffer. */

+ s := buf.Slice() + if !bytes.Equal(s, zeroes) { + t.Fatalf("Expected %v, got %v", zeroes, s) + } + + /* Modifing the slice modifies the underlying buffer. */

} + +// Benchmark creating a slice without copying the underling buffer.

+func BenchmarkAioBufferSlice(b *testing.B) { + buf := MakeAioBuffer(bufferSize) + defer buf.Free() + var r int + + b.ResetTimer() + for i := 0; i < b.N; i++ { + r += len(buf.Slice()) + } +} -- 2.34.1