Remove usermem dependency from marshal

Both marshal and usermem are depended on by many packages and a dependency on
marshal can often create circular dependencies. marshal should consider adding
internal dependencies carefully moving forward.

Fixes #6160

PiperOrigin-RevId: 379199882

2 files changed, 44 insertions, 0 deletions

diff --git a/pkg/usermem/BUILD b/pkg/usermem/BUILD
index 3dba36f12..d7decd78a 100644
--- a/pkg/usermem/BUILD
+++ b/pkg/usermem/BUILD
@@ -7,6 +7,7 @@ go_library(
     srcs = [
         "bytes_io.go",
         "bytes_io_unsafe.go",
+        "marshal.go",
         "usermem.go",
     ],
     visibility = ["//:sandbox"],
diff --git a/pkg/usermem/marshal.go b/pkg/usermem/marshal.go
new file mode 100644
index 000000000..5b5a662dc
--- /dev/null
+++ b/pkg/usermem/marshal.go
@@ -0,0 +1,43 @@
+// Copyright 2021 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package usermem
+
+import (
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/hostarch"
+)
+
+// IOCopyContext wraps an object implementing hostarch.IO to implement
+// marshal.CopyContext.
+type IOCopyContext struct {
+	Ctx  context.Context
+	IO   IO
+	Opts IOOpts
+}
+
+// CopyScratchBuffer implements marshal.CopyContext.CopyScratchBuffer.
+func (i *IOCopyContext) CopyScratchBuffer(size int) []byte {
+	return make([]byte, size)
+}
+
+// CopyOutBytes implements marshal.CopyContext.CopyOutBytes.
+func (i *IOCopyContext) CopyOutBytes(addr hostarch.Addr, b []byte) (int, error) {
+	return i.IO.CopyOut(i.Ctx, addr, b, i.Opts)
+}
+
+// CopyInBytes implements marshal.CopyContext.CopyInBytes.
+func (i *IOCopyContext) CopyInBytes(addr hostarch.Addr, b []byte) (int, error) {
+	return i.IO.CopyIn(i.Ctx, addr, b, i.Opts)
+}