Decouple filemem from platform and move it to pgalloc.MemoryFile.

This is in preparation for improved page cache reclaim, which requires
greater integration between the page cache and page allocator.

PiperOrigin-RevId: 238444706
Change-Id: Id24141b3678d96c7d7dc24baddd9be555bffafe4

1 files changed, 48 insertions, 0 deletions

diff --git a/pkg/sentry/pgalloc/context.go b/pkg/sentry/pgalloc/context.go
new file mode 100644
index 000000000..adc97e78f
--- /dev/null
+++ b/pkg/sentry/pgalloc/context.go
@@ -0,0 +1,48 @@
+// Copyright 2019 Google Inc.
+//
+// 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 pgalloc
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+)
+
+// contextID is this package's type for context.Context.Value keys.
+type contextID int
+
+const (
+	// CtxMemoryFile is a Context.Value key for a MemoryFile.
+	CtxMemoryFile contextID = iota
+
+	// CtxMemoryFileProvider is a Context.Value key for a MemoryFileProvider.
+	CtxMemoryFileProvider
+)
+
+// MemoryFileFromContext returns the MemoryFile used by ctx, or nil if no such
+// MemoryFile exists.
+func MemoryFileFromContext(ctx context.Context) *MemoryFile {
+	if v := ctx.Value(CtxMemoryFile); v != nil {
+		return v.(*MemoryFile)
+	}
+	return nil
+}
+
+// MemoryFileProviderFromContext returns the MemoryFileProvider used by ctx, or nil if no such
+// MemoryFileProvider exists.
+func MemoryFileProviderFromContext(ctx context.Context) MemoryFileProvider {
+	if v := ctx.Value(CtxMemoryFileProvider); v != nil {
+		return v.(MemoryFileProvider)
+	}
+	return nil
+}