From c03718ca7b5c13483766c84fcbb6cdb41ea254e1 Mon Sep 17 00:00:00 2001
From: Aaron Jacobs <jacobsa@google.com>
Date: Fri, 27 Feb 2015 16:30:22 +1100
Subject: [PATCH] Started on an in-memory file system.

---
 samples/mem_fs.go | 92 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 samples/mem_fs.go

diff --git a/samples/mem_fs.go b/samples/mem_fs.go
new file mode 100644
index 0000000..7e0af09
--- /dev/null
+++ b/samples/mem_fs.go
@@ -0,0 +1,92 @@
+// Copyright 2015 Google Inc. All Rights Reserved.
+// Author: jacobsa@google.com (Aaron Jacobs)
+
+package samples
+
+import (
+	"sync"
+
+	"github.com/jacobsa/fuse"
+	"github.com/jacobsa/fuse/fuseutil"
+	"github.com/jacobsa/gcloud/syncutil"
+	"github.com/jacobsa/gcsfuse/timeutil"
+)
+
+// Create a file system that stores data and metadata in memory.
+func NewMemFS(
+	clock timeutil.Clock) fuse.FileSystem
+
+type memFS struct {
+	fuseutil.NotImplementedFileSystem
+
+	/////////////////////////
+	// Dependencies
+	/////////////////////////
+
+	clock timeutil.Clock
+
+	/////////////////////////
+	// Mutable state
+	/////////////////////////
+
+	mu syncutil.InvariantMutex
+
+	// The next inode to issue.
+	//
+	// INVARIANT: nextInode > 0
+	nextInode fuse.InodeID // GUARDED_BY(mu)
+
+	// A map from inode number to file or directory with that inode.
+	//
+	// INVARIANT: inodeIndex[fuse.RootInodeID != nil
+	// INVARIANT: For all keys k, k > 0
+	// INVARIANT: For all keys k, k < nextInode
+	// INVARIANT: For all keys k, inodeIndex[k] is *memFile or *memDir
+	// INVARIANT: For all keys k, inodeIndex[k].inode == k
+	// INVARIANT: For all dirs d, all of d's children are in the map.
+	inodeIndex map[fuse.InodeID]interface{} // GUARDED_BY(mu)
+}
+
+type memFile struct {
+	/////////////////////////
+	// Constant data
+	/////////////////////////
+
+	inode fuse.InodeID
+
+	/////////////////////////
+	// Mutable state
+	/////////////////////////
+
+	mu sync.RWMutex
+
+	// The current contents of the file.
+	contents []byte // GUARDED_BY(mu)
+}
+
+// TODO(jacobsa): Add a test that various WriteAt calls with a real on-disk
+// file to verify what the behavior should be here, particularly when starting
+// a write well beyond EOF. Leave the test around for documentation purposes.
+func (f *memFile) WriteAt(p []byte, off int64) (n int, err error)
+
+type memDir struct {
+	/////////////////////////
+	// Constant data
+	/////////////////////////
+
+	inode fuse.InodeID
+
+	/////////////////////////
+	// Mutable state
+	/////////////////////////
+
+	mu syncutil.InvariantMutex
+
+	// The contents of the directory. An entry with inode zero is unused.
+	//
+	// This array can never be shortened, nor can its elements be moved, because
+	// we use its indices for Dirent.Offset, which is exposed to the user who
+	// might be calling readdir in a loop while concurrently modifying the
+	// directory. Unused entries can, however, be reused.
+	entries []fuseutil.Dirent
+}