Initial QSfera import

Server/vendor/github.com/ceph/go-ceph/internal/cutil/ptrguard.go

@@ -0,0 +1,37 @@
+//go:build !go1.21
+// +build !go1.21
+
+// This code assumes a non-moving garbage collector, which is the case until at
+// least go 1.20
+
+package cutil
+
+import (
+	"unsafe"
+)
+
+// PtrGuard respresents a guarded Go pointer (pointing to memory allocated by Go
+// runtime) stored in C memory (allocated by C)
+type PtrGuard struct {
+	cPtr  CPtr
+	goPtr unsafe.Pointer
+}
+
+// NewPtrGuard writes the goPtr (pointing to Go memory) into C memory at the
+// position cPtr, and returns a PtrGuard object.
+func NewPtrGuard(cPtr CPtr, goPtr unsafe.Pointer) *PtrGuard {
+	var v PtrGuard
+	v.cPtr = cPtr
+	v.goPtr = goPtr
+	p := (*unsafe.Pointer)(unsafe.Pointer(cPtr))
+	*p = goPtr
+	return &v
+}
+
+// Release removes the guarded Go pointer from the C memory by overwriting it
+// with NULL.
+func (v *PtrGuard) Release() {
+	p := (*unsafe.Pointer)(unsafe.Pointer(v.cPtr))
+	*p = nil
+	v.goPtr = nil
+}