rados: implement binding for rados_write_op_cmpext

This commit implements binding for rados_write_op_cmpext RADOS Write operation.
Includes a unit test.

Signed-off-by: Robert Vasek <robert.vasek@cern.ch>

docs/api-status.json

@@ -925,6 +925,14 @@
         "name": "WriteOp.WriteSame",
         "comment": "WriteSame write a given byte slice to the object multiple times, until\nwriteLen is satisfied.\n\nImplements:\n void rados_write_op_writesame(rados_write_op_t write_op,\n                               const char *buffer,\n                               size_t data_len,\n                               size_t write_len,\n                               uint64_t offset);\n"
       }
+    ],
+    "preview_api": [
+      {
+        "name": "WriteOp.CmpExt",
+        "comment": "CmpExt ensures that given object range (extent) satisfies comparison.\n PREVIEW\n\nImplements:\n void rados_write_op_cmpext(rados_write_op_t write_op,\n                            const char * cmp_buf,\n                            size_t cmp_len,\n                            uint64_t off,\n                            int * prval);\n",
+        "added_in_version": "v0.12.0",
+        "expected_stable_version": "v0.14.0"
+      }
     ]
   },
   "rbd": {

docs/api-status.md

@@ -8,6 +8,12 @@
 
 ## Package: rados
 
+### Preview APIs
+
+Name | Added in Version | Expected Stable Version | 
+---- | ---------------- | ----------------------- | 
+WriteOp.CmpExt | v0.12.0 | v0.14.0 | 
+
 ## Package: rbd
 
 ### Deprecated APIs
@@ -20,10 +26,10 @@ Snapshot.Set | v0.10.0 |  |
 
 ## Package: rbd/admin
 
-### Preview APIs
-
 ## Package: rgw/admin
 
 ### Preview APIs
 
+Name | Added in Version | Expected Stable Version | 
+---- | ---------------- | ----------------------- | 
 

internal/cutil/aliases.go

@@ -23,6 +23,9 @@ const (
 	SizeTSize = C.sizeof_size_t
 )
 
+// Compile-time assertion ensuring that Go's `int` is at least as large as C's.
+const _ = unsafe.Sizeof(int(0)) - C.sizeof_int
+
 // SizeT wraps size_t from C.
 type SizeT C.size_t
 

rados/write_op_preview.go

@@ -0,0 +1,63 @@
+//go:build ceph_preview
+// +build ceph_preview
+
+package rados
+
+// #cgo LDFLAGS: -lrados
+// #include <rados/librados.h>
+// #include <stdlib.h>
+//
+import "C"
+
+import (
+	"unsafe"
+)
+
+// WriteOpCmpExtStep holds result of the CmpExt write operation.
+// Result is valid only after Operate() was called.
+type WriteOpCmpExtStep struct {
+	// C returned data:
+	prval *C.int
+
+	// Result of the CmpExt write operation.
+	Result int
+}
+
+func (s *WriteOpCmpExtStep) update() error {
+	s.Result = int(*s.prval)
+	return nil
+}
+
+func (s *WriteOpCmpExtStep) free() {
+	C.free(unsafe.Pointer(s.prval))
+	s.prval = nil
+}
+
+func newWriteOpCmpExtStep() *WriteOpCmpExtStep {
+	return &WriteOpCmpExtStep{
+		prval: (*C.int)(C.malloc(C.sizeof_int)),
+	}
+}
+
+// CmpExt ensures that given object range (extent) satisfies comparison.
+//  PREVIEW
+//
+// Implements:
+//  void rados_write_op_cmpext(rados_write_op_t write_op,
+//                             const char * cmp_buf,
+//                             size_t cmp_len,
+//                             uint64_t off,
+//                             int * prval);
+func (w *WriteOp) CmpExt(b []byte, offset uint64) *WriteOpCmpExtStep {
+	oe := newWriteStep(b, 0, offset)
+	cmpExtStep := newWriteOpCmpExtStep()
+	w.steps = append(w.steps, oe, cmpExtStep)
+	C.rados_write_op_cmpext(
+		w.op,
+		oe.cBuffer,
+		oe.cDataLen,
+		oe.cOffset,
+		cmpExtStep.prval)
+
+	return cmpExtStep
+}

rados/write_op_preview_test.go

@@ -0,0 +1,40 @@
+//go:build ceph_preview
+// +build ceph_preview
+
+package rados
+
+import (
+	"github.com/stretchr/testify/assert"
+)
+
+func (suite *RadosTestSuite) TestWriteOpCmpExt() {
+	suite.SetupConnection()
+	ta := assert.New(suite.T())
+
+	oid := "TestWriteOpCmpExt"
+	data := []byte("compare this")
+
+	// Create an object and populate it with data.
+	op1 := CreateWriteOp()
+	defer op1.Release()
+	op1.Create(CreateIdempotent)
+	op1.WriteFull([]byte(data))
+	err := op1.Operate(suite.ioctx, oid, OperationNoFlag)
+	ta.NoError(err)
+
+	// Compare contents of the object. Should succeed.
+	op2 := CreateWriteOp()
+	defer op2.Release()
+	cmpExtRes1 := op2.CmpExt(data, 0)
+	err = op2.Operate(suite.ioctx, oid, OperationNoFlag)
+	ta.NoError(err)
+	ta.Equal(cmpExtRes1.Result, int(0))
+
+	// Compare contents of the object. Should fail.
+	op3 := CreateWriteOp()
+	defer op3.Release()
+	cmpExtRes2 := op3.CmpExt([]byte("xxx"), 0)
+	err = op3.Operate(suite.ioctx, oid, OperationNoFlag)
+	ta.Error(err)
+	ta.NotEqual(cmpExtRes2.Result, int(0))
+}