386 lines
8.6 KiB
Go
386 lines
8.6 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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"context"
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"fmt"
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"os"
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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/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 unexpected reference counts remaining, after
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// unmounting.
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func NewFileSystem() *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{
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attributes: fuseops.InodeAttributes{
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Nlink: 1,
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Mode: 0777 | os.ModeDir,
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},
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},
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cannedID_Foo: &inode{
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attributes: fuseops.InodeAttributes{
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Nlink: 1,
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Mode: 0777,
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},
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},
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cannedID_Bar: &inode{
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attributes: fuseops.InodeAttributes{
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Nlink: 1,
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Mode: 0777 | os.ModeDir,
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},
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},
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},
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nextInodeID: cannedID_Next,
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}
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// The root inode starts with a lookup count of one.
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impl.inodes[cannedID_Root].IncrementLookupCount()
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// The canned inodes are supposed to be stable from the user's point of view,
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// so we should allow them to be looked up at any point even if the kernel
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// has balanced its lookups with its forgets. Ensure that they never go to
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// zero until the file system is destroyed.
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impl.inodes[cannedID_Foo].IncrementLookupCount()
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impl.inodes[cannedID_Bar].IncrementLookupCount()
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// Set up the mutex.
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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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return &ForgetFS{
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impl: impl,
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server: fuseutil.NewFileSystemServer(impl),
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}
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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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// 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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////////////////////////////////////////////////////////////////////////
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// inode
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////////////////////////////////////////////////////////////////////////
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type inode struct {
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attributes fuseops.InodeAttributes
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// The current lookup count.
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lookupCount uint64
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// true if lookupCount has ever been positive.
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lookedUp bool
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}
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func (in *inode) Forgotten() bool {
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return in.lookedUp && in.lookupCount == 0
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}
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func (in *inode) IncrementLookupCount() {
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in.lookupCount++
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in.lookedUp = true
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}
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func (in *inode) DecrementLookupCount(n uint64) {
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if in.lookupCount < n {
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panic(fmt.Sprintf(
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"Overly large decrement: %v, %v",
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in.lookupCount,
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n))
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}
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in.lookupCount -= n
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}
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// Decrement the lookup count to zero.
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func (in *inode) Destroy() {
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in.DecrementLookupCount(in.lookupCount)
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}
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////////////////////////////////////////////////////////////////////////
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// Helpers
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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 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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// Look up the inode and verify it hasn't been forgotten.
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//
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// LOCKS_REQUIRED(fs.mu)
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func (fs *fsImpl) findInodeByID(id fuseops.InodeID) *inode {
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in := fs.inodes[id]
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if in == nil {
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panic(fmt.Sprintf("Unknown inode: %v", id))
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}
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if in.Forgotten() {
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panic(fmt.Sprintf("Forgotten inode: %v", id))
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}
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return in
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}
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////////////////////////////////////////////////////////////////////////
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// FileSystem methods
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////////////////////////////////////////////////////////////////////////
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func (fs *fsImpl) StatFS(
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ctx context.Context,
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op *fuseops.StatFSOp) error {
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return nil
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}
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func (fs *fsImpl) LookUpInode(
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ctx context.Context,
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op *fuseops.LookUpInodeOp) error {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Make sure the parent exists and has not been forgotten.
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_ = fs.findInodeByID(op.Parent)
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// Handle the names we support.
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var childID fuseops.InodeID
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switch {
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case op.Parent == cannedID_Root && op.Name == "foo":
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childID = cannedID_Foo
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case op.Parent == cannedID_Root && op.Name == "bar":
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childID = cannedID_Bar
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default:
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return fuse.ENOENT
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}
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// Look up the child.
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child := fs.findInodeByID(childID)
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child.IncrementLookupCount()
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// Return an appropriate entry.
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op.Entry = fuseops.ChildInodeEntry{
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Child: childID,
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Attributes: child.attributes,
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}
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return nil
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}
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func (fs *fsImpl) GetInodeAttributes(
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ctx context.Context,
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op *fuseops.GetInodeAttributesOp) error {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Find the inode, verifying that it has not been forgotten.
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in := fs.findInodeByID(op.Inode)
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// Return appropriate attributes.
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op.Attributes = in.attributes
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return nil
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}
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func (fs *fsImpl) ForgetInode(
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ctx context.Context,
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op *fuseops.ForgetInodeOp) error {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Find the inode and decrement its count.
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in := fs.findInodeByID(op.Inode)
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in.DecrementLookupCount(op.N)
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return nil
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}
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func (fs *fsImpl) MkDir(
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ctx context.Context,
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op *fuseops.MkDirOp) error {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Make sure the parent exists and has not been forgotten.
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_ = fs.findInodeByID(op.Parent)
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// Mint a child inode.
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childID := fs.nextInodeID
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fs.nextInodeID++
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child := &inode{
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attributes: fuseops.InodeAttributes{
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Nlink: 0,
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Mode: 0777 | os.ModeDir,
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},
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}
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fs.inodes[childID] = child
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child.IncrementLookupCount()
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// Return an appropriate entry.
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op.Entry = fuseops.ChildInodeEntry{
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Child: childID,
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Attributes: child.attributes,
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}
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return nil
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}
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func (fs *fsImpl) CreateFile(
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ctx context.Context,
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op *fuseops.CreateFileOp) error {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Make sure the parent exists and has not been forgotten.
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_ = fs.findInodeByID(op.Parent)
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// Mint a child inode.
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childID := fs.nextInodeID
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fs.nextInodeID++
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child := &inode{
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attributes: fuseops.InodeAttributes{
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Nlink: 0,
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Mode: 0777,
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},
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}
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fs.inodes[childID] = child
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child.IncrementLookupCount()
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// Return an appropriate entry.
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op.Entry = fuseops.ChildInodeEntry{
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Child: childID,
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Attributes: child.attributes,
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}
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return nil
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}
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func (fs *fsImpl) OpenFile(
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ctx context.Context,
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op *fuseops.OpenFileOp) error {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Verify that the inode has not been forgotten.
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_ = fs.findInodeByID(op.Inode)
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return nil
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}
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func (fs *fsImpl) OpenDir(
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ctx context.Context,
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op *fuseops.OpenDirOp) error {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Verify that the inode has not been forgotten.
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_ = fs.findInodeByID(op.Inode)
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return nil
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}
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func (fs *fsImpl) Destroy() {
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for _, in := range fs.inodes {
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in.Destroy()
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}
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}
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