373 lines
8.2 KiB
Go
373 lines
8.2 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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"context"
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"crypto/rand"
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"fmt"
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"io"
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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/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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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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//
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// Each file responds to reads with random contents. SetKeepCache can be used
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// to control whether the response to OpenFileOp tells the kernel to keep the
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// file's data in the page cache or not.
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type CachingFS interface {
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fuseutil.FileSystem
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// Return the current inode ID of the file/directory with the given name.
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FooID() fuseops.InodeID
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DirID() fuseops.InodeID
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BarID() fuseops.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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// Instruct the file system whether or not to reply to OpenFileOp with
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// FOPEN_KEEP_CACHE set.
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SetKeepCache(keep bool)
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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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func NewCachingFS(
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lookupEntryTimeout time.Duration,
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getattrTimeout time.Duration) (CachingFS, error) {
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roundUp := func(n fuseops.InodeID) fuseops.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(fuseops.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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return cfs, nil
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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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// GUARDED_BY(mu)
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keepPageCache bool
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// The current ID of the lowest numbered non-root inode.
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//
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// INVARIANT: baseID > fuseops.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 fuseops.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 > fuseops.RootInodeID
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// INVARIANT: baseID % numInodes == 0
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if fs.baseID <= fuseops.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() fuseops.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() fuseops.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() fuseops.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() fuseops.InodeAttributes {
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return fuseops.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() fuseops.InodeAttributes {
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return fuseops.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() fuseops.InodeAttributes {
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return fuseops.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() fuseops.InodeAttributes {
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return fuseops.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() fuseops.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() fuseops.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() fuseops.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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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) SetKeepCache(keep bool) {
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fs.mu.Lock()
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defer fs.mu.Unlock()
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fs.keepPageCache = keep
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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) 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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// LOCKS_EXCLUDED(fs.mu)
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func (fs *cachingFS) 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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// Find the ID and attributes.
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var id fuseops.InodeID
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var attrs fuseops.InodeAttributes
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switch op.Name {
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case "foo":
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// Parent must be the root.
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if op.Parent != fuseops.RootInodeID {
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return fuse.ENOENT
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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 op.Parent != fuseops.RootInodeID {
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return fuse.ENOENT
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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 op.Parent == fuseops.RootInodeID || op.Parent%numInodes != dirOffset {
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return fuse.ENOENT
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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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return fuse.ENOENT
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}
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// Fill in the response.
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op.Entry.Child = id
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op.Entry.Attributes = attrs
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op.Entry.EntryExpiration = time.Now().Add(fs.lookupEntryTimeout)
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return nil
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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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op *fuseops.GetInodeAttributesOp) error {
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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 fuseops.InodeAttributes
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switch {
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case op.Inode == fuseops.RootInodeID:
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attrs = fs.rootAttrs()
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case op.Inode%numInodes == fooOffset:
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attrs = fs.fooAttrs()
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case op.Inode%numInodes == dirOffset:
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attrs = fs.dirAttrs()
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case op.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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op.Attributes = attrs
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op.AttributesExpiration = time.Now().Add(fs.getattrTimeout)
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return nil
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}
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func (fs *cachingFS) OpenDir(
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ctx context.Context,
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op *fuseops.OpenDirOp) error {
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return nil
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}
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func (fs *cachingFS) 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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op.KeepPageCache = fs.keepPageCache
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return nil
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}
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func (fs *cachingFS) ReadFile(
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ctx context.Context,
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op *fuseops.ReadFileOp) error {
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var err error
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op.BytesRead, err = io.ReadFull(rand.Reader, op.Dst)
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return err
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}
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