rados: add Write, WriteFull, and WriteSame WriteOp functions

Add Write implementing rados_write_op_write.
Add WriteFull implementing rados_write_op_write_full.
Add WriteSame implementing rados_write_op_writesame.

These are some of the basic functions needed to write data to
a rados object using a WriteOp.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

rados/write_op.go

@@ -124,3 +124,56 @@ func (w *WriteOp) CleanOmap() {
 func (w *WriteOp) AssertExists() {
 	C.rados_write_op_assert_exists(w.op)
 }
+
+// Write a given byte slice at the supplied offset.
+//
+// Implements:
+//  void rados_write_op_write(rados_write_op_t write_op,
+//                                       const char *buffer,
+//                                       size_t len,
+//                                       uint64_t offset);
+func (w *WriteOp) Write(b []byte, offset uint64) {
+	oe := newWriteStep(b, 0, offset)
+	w.steps = append(w.steps, oe)
+	C.rados_write_op_write(
+		w.op,
+		oe.cBuffer,
+		oe.cDataLen,
+		oe.cOffset)
+}
+
+// WriteFull writes a given byte slice as the whole object,
+// atomically replacing it.
+//
+// Implements:
+//  void rados_write_op_write_full(rados_write_op_t write_op,
+//                                 const char *buffer,
+//                                 size_t len);
+func (w *WriteOp) WriteFull(b []byte) {
+	oe := newWriteStep(b, 0, 0)
+	w.steps = append(w.steps, oe)
+	C.rados_write_op_write_full(
+		w.op,
+		oe.cBuffer,
+		oe.cDataLen)
+}
+
+// WriteSame write a given byte slice to the object multiple times, until
+// writeLen is satisfied.
+//
+// Implements:
+//  void rados_write_op_writesame(rados_write_op_t write_op,
+//                                const char *buffer,
+//                                size_t data_len,
+//                                size_t write_len,
+//                                uint64_t offset);
+func (w *WriteOp) WriteSame(b []byte, writeLen, offset uint64) {
+	oe := newWriteStep(b, writeLen, offset)
+	w.steps = append(w.steps, oe)
+	C.rados_write_op_writesame(
+		w.op,
+		oe.cBuffer,
+		oe.cDataLen,
+		oe.cWriteLen,
+		oe.cOffset)
+}

rados/write_step.go

@@ -0,0 +1,33 @@
+package rados
+
+// #include <stdint.h>
+import "C"
+
+import (
+	"unsafe"
+)
+
+type writeStep struct {
+	withoutUpdate
+	withoutFree
+	// the c pointer utilizes the Go byteslice data and no free is needed
+
+	// inputs:
+	b []byte
+
+	// arguments:
+	cBuffer   *C.char
+	cDataLen  C.size_t
+	cWriteLen C.size_t
+	cOffset   C.uint64_t
+}
+
+func newWriteStep(b []byte, writeLen, offset uint64) *writeStep {
+	return &writeStep{
+		b:         b,
+		cBuffer:   (*C.char)(unsafe.Pointer(&b[0])),
+		cDataLen:  C.size_t(len(b)),
+		cWriteLen: C.size_t(writeLen),
+		cOffset:   C.uint64_t(offset),
+	}
+}