rados: add an initial ReadOp type for rados read operations

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

rados/read_op.go

@@ -0,0 +1,57 @@
+package rados
+
+// #cgo LDFLAGS: -lrados
+// #include <errno.h>
+// #include <stdlib.h>
+// #include <rados/librados.h>
+//
+import "C"
+
+import (
+	"unsafe"
+)
+
+// ReadOp manages a set of discrete object read actions that will be performed
+// together atomically.
+type ReadOp struct {
+	operation
+	op C.rados_read_op_t
+}
+
+// CreateReadOp returns a newly constructed read operation.
+func CreateReadOp() *ReadOp {
+	return &ReadOp{
+		op: C.rados_create_read_op(),
+	}
+}
+
+// Release the resources associated with this read operation.
+func (r *ReadOp) Release() {
+	C.rados_release_read_op(r.op)
+	r.op = nil
+	r.free()
+}
+
+// Operate will perform the operation(s).
+func (r *ReadOp) Operate(ioctx *IOContext, oid string, flags OperationFlags) error {
+	if err := ioctx.validate(); err != nil {
+		return err
+	}
+
+	cOid := C.CString(oid)
+	defer C.free(unsafe.Pointer(cOid))
+
+	ret := C.rados_read_op_operate(r.op, ioctx.ioctx, cOid, C.int(flags))
+	return r.update(readOp, ret)
+}
+
+func (r *ReadOp) operateCompat(ioctx *IOContext, oid string) error {
+	switch err := r.Operate(ioctx, oid, OperationNoFlag).(type) {
+	case nil:
+		return nil
+	case OperationError:
+		return err.OpError
+	default:
+		return err
+	}
+}