354 lines
7.8 KiB
Go
354 lines
7.8 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 cachingfs
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import (
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"fmt"
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"os"
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"time"
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"github.com/jacobsa/fuse"
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"github.com/jacobsa/fuse/fuseutil"
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"github.com/jacobsa/gcloud/syncutil"
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"golang.org/x/net/context"
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)
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const (
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// Sizes of the files according to the file system.
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FooSize = 123
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BarSize = 456
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)
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// A file system with a fixed structure that looks like this:
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//
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// foo
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// dir/
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// bar
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//
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// The file system is configured with durations that specify how long to allow
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// inode entries and attributes to be cached, used when responding to fuse
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// requests. It also exposes methods for renumbering inodes and updating mtimes
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// that are useful in testing that these durations are honored.
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type CachingFS interface {
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fuse.FileSystem
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// Return the current inode ID of the file/directory with the given name.
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FooID() fuse.InodeID
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DirID() fuse.InodeID
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BarID() fuse.InodeID
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// Cause the inode IDs to change to values that have never before been used.
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RenumberInodes()
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// Cause further queries for the attributes of inodes to use the supplied
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// time as the inode's mtime.
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SetMtime(mtime time.Time)
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}
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// Create a file system that issues cacheable responses according to the
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// following rules:
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//
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// * LookUpInodeResponse.Entry.EntryExpiration is set according to
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// lookupEntryTimeout.
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//
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// * GetInodeAttributesResponse.AttributesExpiration is set according to
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// getattrTimeout.
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//
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// * Nothing else is marked cacheable. (In particular, the attributes
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// returned by LookUpInode are not cacheable.)
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//
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func NewCachingFS(
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lookupEntryTimeout time.Duration,
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getattrTimeout time.Duration) (fs CachingFS, err error) {
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roundUp := func(n fuse.InodeID) fuse.InodeID {
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return numInodes * ((n + numInodes - 1) / numInodes)
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}
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cfs := &cachingFS{
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lookupEntryTimeout: lookupEntryTimeout,
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getattrTimeout: getattrTimeout,
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baseID: roundUp(fuse.RootInodeID + 1),
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mtime: time.Now(),
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}
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cfs.mu = syncutil.NewInvariantMutex(cfs.checkInvariants)
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fs = cfs
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return
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}
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const (
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// Inode IDs are issued such that "foo" always receives an ID that is
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// congruent to fooOffset modulo numInodes, etc.
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fooOffset = iota
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dirOffset
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barOffset
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numInodes
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)
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type cachingFS struct {
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fuseutil.NotImplementedFileSystem
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/////////////////////////
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// Constant data
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/////////////////////////
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lookupEntryTimeout time.Duration
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getattrTimeout time.Duration
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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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// The current ID of the lowest numbered non-root inode.
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//
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// INVARIANT: baseID > fuse.RootInodeID
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// INVARIANT: baseID % numInodes == 0
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//
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// GUARDED_BY(mu)
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baseID fuse.InodeID
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// GUARDED_BY(mu)
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mtime time.Time
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}
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////////////////////////////////////////////////////////////////////////
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// Helpers
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////////////////////////////////////////////////////////////////////////
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func (fs *cachingFS) checkInvariants() {
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// INVARIANT: baseID > fuse.RootInodeID
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// INVARIANT: baseID % numInodes == 0
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if fs.baseID <= fuse.RootInodeID || fs.baseID%numInodes != 0 {
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panic(fmt.Sprintf("Bad baseID: %v", fs.baseID))
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}
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *cachingFS) fooID() fuse.InodeID {
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return fs.baseID + fooOffset
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *cachingFS) dirID() fuse.InodeID {
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return fs.baseID + dirOffset
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *cachingFS) barID() fuse.InodeID {
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return fs.baseID + barOffset
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *cachingFS) rootAttrs() fuse.InodeAttributes {
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return fuse.InodeAttributes{
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Mode: os.ModeDir | 0777,
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Mtime: fs.mtime,
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}
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *cachingFS) fooAttrs() fuse.InodeAttributes {
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return fuse.InodeAttributes{
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Nlink: 1,
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Size: FooSize,
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Mode: 0777,
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Mtime: fs.mtime,
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}
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *cachingFS) dirAttrs() fuse.InodeAttributes {
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return fuse.InodeAttributes{
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Nlink: 1,
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Mode: os.ModeDir | 0777,
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Mtime: fs.mtime,
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}
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}
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// LOCKS_REQUIRED(fs.mu)
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func (fs *cachingFS) barAttrs() fuse.InodeAttributes {
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return fuse.InodeAttributes{
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Nlink: 1,
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Size: BarSize,
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Mode: 0777,
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Mtime: fs.mtime,
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}
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}
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////////////////////////////////////////////////////////////////////////
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// Public interface
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////////////////////////////////////////////////////////////////////////
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) FooID() fuse.InodeID {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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return fs.fooID()
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}
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) DirID() fuse.InodeID {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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return fs.dirID()
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}
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) BarID() fuse.InodeID {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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return fs.barID()
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}
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) RenumberInodes() {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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fs.baseID += numInodes
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}
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) SetMtime(mtime time.Time) {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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fs.mtime = mtime
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}
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////////////////////////////////////////////////////////////////////////
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// FileSystem methods
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////////////////////////////////////////////////////////////////////////
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func (fs *cachingFS) Init(
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ctx context.Context,
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req *fuse.InitRequest) (resp *fuse.InitResponse, err error) {
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resp = &fuse.InitResponse{}
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return
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}
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) LookUpInode(
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ctx context.Context,
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req *fuse.LookUpInodeRequest) (resp *fuse.LookUpInodeResponse, err error) {
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resp = &fuse.LookUpInodeResponse{}
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Find the ID and attributes.
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var id fuse.InodeID
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var attrs fuse.InodeAttributes
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switch req.Name {
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case "foo":
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// Parent must be the root.
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if req.Parent != fuse.RootInodeID {
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err = fuse.ENOENT
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return
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}
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id = fs.fooID()
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attrs = fs.fooAttrs()
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case "dir":
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// Parent must be the root.
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if req.Parent != fuse.RootInodeID {
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err = fuse.ENOENT
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return
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}
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id = fs.dirID()
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attrs = fs.dirAttrs()
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case "bar":
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// Parent must be dir.
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if req.Parent == fuse.RootInodeID || req.Parent%numInodes != dirOffset {
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err = fuse.ENOENT
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return
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}
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id = fs.barID()
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attrs = fs.barAttrs()
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default:
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err = fuse.ENOENT
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return
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}
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// Fill in the response.
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resp.Entry.Child = id
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resp.Entry.Attributes = attrs
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resp.Entry.EntryExpiration = time.Now().Add(fs.lookupEntryTimeout)
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return
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}
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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) GetInodeAttributes(
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ctx context.Context,
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req *fuse.GetInodeAttributesRequest) (
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resp *fuse.GetInodeAttributesResponse, err error) {
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resp = &fuse.GetInodeAttributesResponse{}
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fs.mu.Lock()
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defer fs.mu.Unlock()
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// Figure out which inode the request is for.
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var attrs fuse.InodeAttributes
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switch {
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case req.Inode == fuse.RootInodeID:
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attrs = fs.rootAttrs()
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case req.Inode%numInodes == fooOffset:
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attrs = fs.fooAttrs()
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case req.Inode%numInodes == dirOffset:
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attrs = fs.dirAttrs()
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case req.Inode%numInodes == barOffset:
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attrs = fs.barAttrs()
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}
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// Fill in the response.
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resp.Attributes = attrs
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resp.AttributesExpiration = time.Now().Add(fs.getattrTimeout)
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return
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}
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func (fs *cachingFS) OpenDir(
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ctx context.Context,
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req *fuse.OpenDirRequest) (
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resp *fuse.OpenDirResponse, err error) {
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resp = &fuse.OpenDirResponse{}
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return
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}
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func (fs *cachingFS) OpenFile(
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ctx context.Context,
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req *fuse.OpenFileRequest) (
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resp *fuse.OpenFileResponse, err error) {
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resp = &fuse.OpenFileResponse{}
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return
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}
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