156 lines
3.8 KiB
Go
156 lines
3.8 KiB
Go
// Copyright 2015 Google Inc. All Rights Reserved.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package forgetfs
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import (
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"fmt"
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"github.com/jacobsa/fuse"
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"github.com/jacobsa/fuse/fuseops"
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"github.com/jacobsa/fuse/fuseutil"
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"github.com/jacobsa/gcloud/syncutil"
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)
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// Create a file system whose sole contents are a file named "foo" and a
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// directory named "bar".
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//
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// The file "foo" may be opened for reading and/or writing, but reads and
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// writes aren't supported. Additionally, any non-existent file or directory
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// name may be created within any directory, but the resulting inode will
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// appear to have been unlinked immediately.
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//
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// The file system maintains reference counts for the inodes involved. It will
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// panic if a reference count becomes negative or if an inode ID is re-used
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// after we expect it to be dead. Its Check method may be used to check that
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// there are no inodes with non-zero reference counts remaining, after
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// unmounting.
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func NewFileSystem() (fs *ForgetFS) {
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// Set up the actual file system.
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impl := &fsImpl{
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inodes: map[fuseops.InodeID]*inode{
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cannedID_Root: &inode{lookupCount: 1},
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cannedID_Foo: &inode{},
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cannedID_Bar: &inode{},
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},
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nextInodeID: cannedID_Next,
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}
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impl.mu = syncutil.NewInvariantMutex(impl.checkInvariants)
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// Set up a wrapper that exposes only certain methods.
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fs = &ForgetFS{
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impl: impl,
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server: fuseutil.NewFileSystemServer(impl),
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}
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return
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}
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////////////////////////////////////////////////////////////////////////
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// ForgetFS
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////////////////////////////////////////////////////////////////////////
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type ForgetFS struct {
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impl *fsImpl
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server fuse.Server
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}
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func (fs *ForgetFS) ServeOps(c *fuse.Connection) {
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fs.server.ServeOps(c)
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}
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// Panic if there are any inodes that have a non-zero reference count. For use
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// after unmounting.
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func (fs *ForgetFS) Check() {
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fs.impl.Check()
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}
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////////////////////////////////////////////////////////////////////////
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// Actual implementation
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////////////////////////////////////////////////////////////////////////
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const (
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cannedID_Root = fuseops.RootInodeID + iota
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cannedID_Foo
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cannedID_Bar
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cannedID_Next
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)
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type fsImpl struct {
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fuseutil.NotImplementedFileSystem
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/////////////////////////
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// Mutable state
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/////////////////////////
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mu syncutil.InvariantMutex
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// An index of inode by ID, for all IDs we have issued.
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//
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// INVARIANT: For each v in inodes, v.lookupCount >= 0
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//
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// GUARDED_BY(mu)
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inodes map[fuseops.InodeID]*inode
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// The next ID to issue.
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//
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// INVARIANT: For each k in inodes, k < nextInodeID
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//
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// GUARDED_BY(mu)
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nextInodeID fuseops.InodeID
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}
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type inode struct {
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// The current lookup count.
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lookupCount int
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *fsImpl) checkInvariants() {
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// INVARIANT: For each v in inodes, v.lookupCount >= 0
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for _, v := range fs.inodes {
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if !(v.lookupCount >= 0) {
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panic("Negative lookup count")
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}
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}
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// INVARIANT: For each k in inodes, k < nextInodeID
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for k, _ := range fs.inodes {
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if !(k < fs.nextInodeID) {
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panic("Unexpectedly large inode ID")
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}
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}
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}
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *fsImpl) Check() {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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for k, v := range fs.inodes {
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if v.lookupCount != 0 {
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panic(fmt.Sprintf("Inode %v has lookup count %v", k, v.lookupCount))
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}
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}
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}
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func (fs *fsImpl) Init(
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op *fuseops.InitOp) {
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var err error
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defer fuseutil.RespondToOp(op, &err)
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return
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}
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