1 files changed, 103 insertions, 0 deletions
diff --git a/pkg/sentry/fs/gofer/cache_policy.go b/pkg/sentry/fs/gofer/cache_policy.go
new file mode 100644
index 000000000..eec8c07cb
--- /dev/null
+++ b/pkg/sentry/fs/gofer/cache_policy.go
@@ -0,0 +1,103 @@
+// Copyright 2018 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 gofer
+
+import (
+	"fmt"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+)
+
+// cachePolicy is a 9p cache policy. It has methods that determine what to
+// cache (if anything) for a given inode.
+type cachePolicy int
+
+const (
+	// Cache nothing.
+	cacheNone cachePolicy = iota
+
+	// Use virtual file system cache for everything.
+	cacheAll
+
+	// Use virtual file system cache for everything, but send writes to the
+	// fs agent immediately.
+	cacheAllWritethrough
+)
+
+func parseCachePolicy(policy string) (cachePolicy, error) {
+	switch policy {
+	case "fscache":
+		return cacheAll, nil
+	case "none":
+		return cacheNone, nil
+	case "fscache_writethrough":
+		return cacheAllWritethrough, nil
+	}
+	return cacheNone, fmt.Errorf("unsupported cache mode: %s", policy)
+}
+
+// cacheUAtters determines whether unstable attributes should be cached for the
+// given inode.
+func (cp cachePolicy) cacheUAttrs(inode *fs.Inode) bool {
+	if !fs.IsFile(inode.StableAttr) && !fs.IsDir(inode.StableAttr) {
+		return false
+	}
+	return cp == cacheAll || cp == cacheAllWritethrough
+}
+
+// cacheReaddir determines whether readdir results should be cached.
+func (cp cachePolicy) cacheReaddir() bool {
+	return cp == cacheAll || cp == cacheAllWritethrough
+}
+
+// usePageCache determines whether the page cache should be used for the given
+// inode.
+func (cp cachePolicy) usePageCache(inode *fs.Inode) bool {
+	// Do cached IO for regular files only. Some "character devices" expect
+	// no caching.
+	if !fs.IsFile(inode.StableAttr) {
+		return false
+	}
+	return cp == cacheAll || cp == cacheAllWritethrough
+}
+
+// writeThough indicates whether writes to the file should be synced to the
+// gofer immediately.
+func (cp cachePolicy) writeThrough(inode *fs.Inode) bool {
+	return cp == cacheNone || cp == cacheAllWritethrough
+}
+
+// revalidateDirent indicates that dirents should be revalidated after they are
+// looked up.
+func (cp cachePolicy) revalidateDirent() bool {
+	return cp == cacheNone
+}
+
+// keepDirent indicates that dirents should be kept pinned in the dirent tree
+// even if there are no application references on the file.
+func (cp cachePolicy) keepDirent(inode *fs.Inode) bool {
+	if cp == cacheNone {
+		return false
+	}
+	sattr := inode.StableAttr
+	// NOTE: Only cache files, directories, and symlinks.
+	return fs.IsFile(sattr) || fs.IsDir(sattr) || fs.IsSymlink(sattr)
+}
+
+// cacheNegativeDirents indicates that negative dirents should be held in the
+// dirent tree.
+func (cp cachePolicy) cacheNegativeDirents() bool {
+	return cp == cacheAll || cp == cacheAllWritethrough
+}