fusego/samples/cachingfs/caching_fs.go

378 lines
8.3 KiB
Go

// Copyright 2015 Google Inc. All Rights Reserved.
//
// 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 cachingfs
import (
"context"
"crypto/rand"
"fmt"
"io"
"os"
"time"
"github.com/jacobsa/fuse"
"github.com/jacobsa/fuse/fuseops"
"github.com/jacobsa/fuse/fuseutil"
"github.com/jacobsa/syncutil"
)
const (
// Sizes of the files according to the file system.
FooSize = 123
BarSize = 456
)
// A file system with a fixed structure that looks like this:
//
// foo
// dir/
// bar
//
// The file system is configured with durations that specify how long to allow
// inode entries and attributes to be cached, used when responding to fuse
// requests. It also exposes methods for renumbering inodes and updating mtimes
// that are useful in testing that these durations are honored.
//
// Each file responds to reads with random contents. SetKeepCache can be used
// to control whether the response to OpenFileOp tells the kernel to keep the
// file's data in the page cache or not.
type CachingFS interface {
fuseutil.FileSystem
// Return the current inode ID of the file/directory with the given name.
FooID() fuseops.InodeID
DirID() fuseops.InodeID
BarID() fuseops.InodeID
// Cause the inode IDs to change to values that have never before been used.
RenumberInodes()
// Cause further queries for the attributes of inodes to use the supplied
// time as the inode's mtime.
SetMtime(mtime time.Time)
// Instruct the file system whether or not to reply to OpenFileOp with
// FOPEN_KEEP_CACHE set.
SetKeepCache(keep bool)
}
// Create a file system that issues cacheable responses according to the
// following rules:
//
// * LookUpInodeResponse.Entry.EntryExpiration is set according to
// lookupEntryTimeout.
//
// * GetInodeAttributesResponse.AttributesExpiration is set according to
// getattrTimeout.
//
// * Nothing else is marked cacheable. (In particular, the attributes
// returned by LookUpInode are not cacheable.)
//
func NewCachingFS(
lookupEntryTimeout time.Duration,
getattrTimeout time.Duration) (fs CachingFS, err error) {
roundUp := func(n fuseops.InodeID) fuseops.InodeID {
return numInodes * ((n + numInodes - 1) / numInodes)
}
cfs := &cachingFS{
lookupEntryTimeout: lookupEntryTimeout,
getattrTimeout: getattrTimeout,
baseID: roundUp(fuseops.RootInodeID + 1),
mtime: time.Now(),
}
cfs.mu = syncutil.NewInvariantMutex(cfs.checkInvariants)
fs = cfs
return
}
const (
// Inode IDs are issued such that "foo" always receives an ID that is
// congruent to fooOffset modulo numInodes, etc.
fooOffset = iota
dirOffset
barOffset
numInodes
)
type cachingFS struct {
fuseutil.NotImplementedFileSystem
/////////////////////////
// Constant data
/////////////////////////
lookupEntryTimeout time.Duration
getattrTimeout time.Duration
/////////////////////////
// Mutable state
/////////////////////////
mu syncutil.InvariantMutex
// GUARDED_BY(mu)
keepPageCache bool
// The current ID of the lowest numbered non-root inode.
//
// INVARIANT: baseID > fuseops.RootInodeID
// INVARIANT: baseID % numInodes == 0
//
// GUARDED_BY(mu)
baseID fuseops.InodeID
// GUARDED_BY(mu)
mtime time.Time
}
////////////////////////////////////////////////////////////////////////
// Helpers
////////////////////////////////////////////////////////////////////////
func (fs *cachingFS) checkInvariants() {
// INVARIANT: baseID > fuseops.RootInodeID
// INVARIANT: baseID % numInodes == 0
if fs.baseID <= fuseops.RootInodeID || fs.baseID%numInodes != 0 {
panic(fmt.Sprintf("Bad baseID: %v", fs.baseID))
}
}
// LOCKS_REQUIRED(fs.mu)
func (fs *cachingFS) fooID() fuseops.InodeID {
return fs.baseID + fooOffset
}
// LOCKS_REQUIRED(fs.mu)
func (fs *cachingFS) dirID() fuseops.InodeID {
return fs.baseID + dirOffset
}
// LOCKS_REQUIRED(fs.mu)
func (fs *cachingFS) barID() fuseops.InodeID {
return fs.baseID + barOffset
}
// LOCKS_REQUIRED(fs.mu)
func (fs *cachingFS) rootAttrs() fuseops.InodeAttributes {
return fuseops.InodeAttributes{
Mode: os.ModeDir | 0777,
Mtime: fs.mtime,
}
}
// LOCKS_REQUIRED(fs.mu)
func (fs *cachingFS) fooAttrs() fuseops.InodeAttributes {
return fuseops.InodeAttributes{
Nlink: 1,
Size: FooSize,
Mode: 0777,
Mtime: fs.mtime,
}
}
// LOCKS_REQUIRED(fs.mu)
func (fs *cachingFS) dirAttrs() fuseops.InodeAttributes {
return fuseops.InodeAttributes{
Nlink: 1,
Mode: os.ModeDir | 0777,
Mtime: fs.mtime,
}
}
// LOCKS_REQUIRED(fs.mu)
func (fs *cachingFS) barAttrs() fuseops.InodeAttributes {
return fuseops.InodeAttributes{
Nlink: 1,
Size: BarSize,
Mode: 0777,
Mtime: fs.mtime,
}
}
////////////////////////////////////////////////////////////////////////
// Public interface
////////////////////////////////////////////////////////////////////////
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) FooID() fuseops.InodeID {
fs.mu.Lock()
defer fs.mu.Unlock()
return fs.fooID()
}
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) DirID() fuseops.InodeID {
fs.mu.Lock()
defer fs.mu.Unlock()
return fs.dirID()
}
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) BarID() fuseops.InodeID {
fs.mu.Lock()
defer fs.mu.Unlock()
return fs.barID()
}
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) RenumberInodes() {
fs.mu.Lock()
defer fs.mu.Unlock()
fs.baseID += numInodes
}
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) SetMtime(mtime time.Time) {
fs.mu.Lock()
defer fs.mu.Unlock()
fs.mtime = mtime
}
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) SetKeepCache(keep bool) {
fs.mu.Lock()
defer fs.mu.Unlock()
fs.keepPageCache = keep
}
////////////////////////////////////////////////////////////////////////
// FileSystem methods
////////////////////////////////////////////////////////////////////////
func (fs *cachingFS) StatFS(
ctx context.Context,
op *fuseops.StatFSOp) (err error) {
return
}
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) LookUpInode(
ctx context.Context,
op *fuseops.LookUpInodeOp) (err error) {
fs.mu.Lock()
defer fs.mu.Unlock()
// Find the ID and attributes.
var id fuseops.InodeID
var attrs fuseops.InodeAttributes
switch op.Name {
case "foo":
// Parent must be the root.
if op.Parent != fuseops.RootInodeID {
err = fuse.ENOENT
return
}
id = fs.fooID()
attrs = fs.fooAttrs()
case "dir":
// Parent must be the root.
if op.Parent != fuseops.RootInodeID {
err = fuse.ENOENT
return
}
id = fs.dirID()
attrs = fs.dirAttrs()
case "bar":
// Parent must be dir.
if op.Parent == fuseops.RootInodeID || op.Parent%numInodes != dirOffset {
err = fuse.ENOENT
return
}
id = fs.barID()
attrs = fs.barAttrs()
default:
err = fuse.ENOENT
return
}
// Fill in the response.
op.Entry.Child = id
op.Entry.Attributes = attrs
op.Entry.EntryExpiration = time.Now().Add(fs.lookupEntryTimeout)
return
}
// LOCKS_EXCLUDED(fs.mu)
func (fs *cachingFS) GetInodeAttributes(
ctx context.Context,
op *fuseops.GetInodeAttributesOp) (err error) {
fs.mu.Lock()
defer fs.mu.Unlock()
// Figure out which inode the request is for.
var attrs fuseops.InodeAttributes
switch {
case op.Inode == fuseops.RootInodeID:
attrs = fs.rootAttrs()
case op.Inode%numInodes == fooOffset:
attrs = fs.fooAttrs()
case op.Inode%numInodes == dirOffset:
attrs = fs.dirAttrs()
case op.Inode%numInodes == barOffset:
attrs = fs.barAttrs()
}
// Fill in the response.
op.Attributes = attrs
op.AttributesExpiration = time.Now().Add(fs.getattrTimeout)
return
}
func (fs *cachingFS) OpenDir(
ctx context.Context,
op *fuseops.OpenDirOp) (err error) {
return
}
func (fs *cachingFS) OpenFile(
ctx context.Context,
op *fuseops.OpenFileOp) (err error) {
fs.mu.Lock()
defer fs.mu.Unlock()
op.KeepPageCache = fs.keepPageCache
return
}
func (fs *cachingFS) ReadFile(
ctx context.Context,
op *fuseops.ReadFileOp) (err error) {
op.BytesRead, err = io.ReadFull(rand.Reader, op.Dst)
return
}