rbd: remove unnecessary C wrapper functions

Signed-off-by: Sven Anderson <sven@redhat.com>

internal/cutil/cutil.go

@@ -0,0 +1,14 @@
+package cutil
+
+import "unsafe"
+
+// VoidPtr casts a uintptr value to an unsafe.Pointer value in order to use it
+// directly as a void* argument in a C function call.
+// CAUTION: NEVER store the result in a variable, or the Go GC could panic.
+func VoidPtr(i uintptr) unsafe.Pointer {
+	var nullPtr unsafe.Pointer
+	// It's not possible to cast uintptr directly to unsafe.Pointer. Therefore we
+	// cast a null pointer to uintptr and apply pointer arithmetic on it, which
+	// allows us to cast it back to unsafe.Pointer.
+	return unsafe.Pointer(uintptr(nullPtr) + i)
+}

internal/cutil/cutil_test.go

@@ -0,0 +1,13 @@
+package cutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestVoidPtr(t *testing.T) {
+	i := uintptr(42)
+	j := uintptr(VoidPtr(i))
+	assert.Equal(t, i, j)
+}

rbd/diff_iterate.go

@@ -7,18 +7,8 @@ package rbd
 #include <stdlib.h>
 #include <rbd/librbd.h>
 
+typedef int (*diff_iterate_callback_t)(uint64_t, size_t, int, void *);
 extern int diffIterateCallback(uint64_t, size_t, int, void *);
-
-// cgo is having trouble converting the callback from the librbd header
-// to a unsafe.Pointer. This shim exists solely to help it along.
-static inline int wrap_rbd_diff_iterate2(
-			rbd_image_t image,
-			const char *fromsnapname,
-			uint64_t ofs, uint64_t len,
-			uint8_t include_parent, uint8_t whole_object,
-			uintptr_t index) {
-	return rbd_diff_iterate2(image, fromsnapname, ofs, len, include_parent, whole_object, diffIterateCallback, (void*)index);
-}
 */
 import "C"
 
@@ -26,6 +16,7 @@ import (
 	"unsafe"
 
 	"github.com/ceph/go-ceph/internal/callbacks"
+	"github.com/ceph/go-ceph/internal/cutil"
 )
 
 var diffIterateCallbacks = callbacks.New()
@@ -110,14 +101,15 @@ func (image *Image) DiffIterate(config DiffIterateConfig) error {
 	cbIndex := diffIterateCallbacks.Add(config)
 	defer diffIterateCallbacks.Remove(cbIndex)
 
-	ret := C.wrap_rbd_diff_iterate2(
+	ret := C.rbd_diff_iterate2(
 		image.image,
 		cSnapName,
 		C.uint64_t(config.Offset),
 		C.uint64_t(config.Length),
 		C.uint8_t(config.IncludeParent),
 		C.uint8_t(config.WholeObject),
-		C.uintptr_t(cbIndex))
+		C.diff_iterate_callback_t(C.diffIterateCallback),
+		cutil.VoidPtr(cbIndex))
 
 	return getError(ret)
 }

rbd/watchers_mimic.go

@@ -9,18 +9,6 @@ package rbd
 #include <rbd/librbd.h>
 
 extern void imageWatchCallback(void *);
-
-// cgo has trouble converting the types of the callback and data arg defined in
-// librbd header. It wants the callback function to be a byte pointer and
-// the arg to be a pointer, which is pretty much the opposite of what we
-// actually want. This shim exists to help coerce the auto-type-conversion
-// to do the right thing for us.
-static inline int wrap_rbd_update_watch(
-			rbd_image_t image,
-			uint64_t *handle,
-			uintptr_t index) {
-	return rbd_update_watch(image, handle, imageWatchCallback, (void*)index);
-}
 */
 import "C"
 
@@ -28,6 +16,7 @@ import (
 	"unsafe"
 
 	"github.com/ceph/go-ceph/internal/callbacks"
+	"github.com/ceph/go-ceph/internal/cutil"
 	"github.com/ceph/go-ceph/internal/retry"
 )
 
@@ -118,10 +107,11 @@ func (image *Image) UpdateWatch(cb WatchCallback, data interface{}) (*Watch, err
 		cbIndex: watchCallbacks.Add(wcc),
 	}
 
-	ret := C.wrap_rbd_update_watch(
+	ret := C.rbd_update_watch(
 		image.image,
 		&w.handle,
-		C.uintptr_t(w.cbIndex))
+		C.rbd_update_callback_t(C.imageWatchCallback),
+		cutil.VoidPtr(w.cbIndex))
 	if ret != 0 {
 		return nil, getError(ret)
 	}