fusego/samples/cachingfs/caching_fs_test.go

726 lines
20 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_test
import (
"bytes"
"io/ioutil"
"os"
"path"
"runtime"
"syscall"
"testing"
"time"
"github.com/jacobsa/fuse/fuseutil"
"github.com/jacobsa/fuse/samples"
"github.com/jacobsa/fuse/samples/cachingfs"
. "github.com/jacobsa/oglematchers"
. "github.com/jacobsa/ogletest"
"github.com/jacobsa/timeutil"
)
func TestCachingFS(t *testing.T) { RunTests(t) }
////////////////////////////////////////////////////////////////////////
// Boilerplate
////////////////////////////////////////////////////////////////////////
type cachingFSTest struct {
samples.SampleTest
fs cachingfs.CachingFS
initialMtime time.Time
}
var _ TearDownInterface = &cachingFSTest{}
func (t *cachingFSTest) setUp(
ti *TestInfo,
lookupEntryTimeout time.Duration,
getattrTimeout time.Duration) {
var err error
// We assert things about whether or not mtimes are cached, but writeback
// caching causes them to always be cached. Turn it off.
t.MountConfig.DisableWritebackCaching = true
// Create the file system.
t.fs, err = cachingfs.NewCachingFS(lookupEntryTimeout, getattrTimeout)
AssertEq(nil, err)
t.Server = fuseutil.NewFileSystemServer(t.fs)
// Mount it.
t.SampleTest.SetUp(ti)
// Set up the mtime.
t.initialMtime = time.Date(2012, 8, 15, 22, 56, 0, 0, time.Local)
t.fs.SetMtime(t.initialMtime)
}
func (t *cachingFSTest) statAll() (foo, dir, bar os.FileInfo) {
var err error
foo, err = os.Stat(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
dir, err = os.Stat(path.Join(t.Dir, "dir"))
AssertEq(nil, err)
bar, err = os.Stat(path.Join(t.Dir, "dir/bar"))
AssertEq(nil, err)
return foo, dir, bar
}
func (t *cachingFSTest) openFiles() (foo, dir, bar *os.File) {
var err error
foo, err = os.Open(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
dir, err = os.Open(path.Join(t.Dir, "dir"))
AssertEq(nil, err)
bar, err = os.Open(path.Join(t.Dir, "dir/bar"))
AssertEq(nil, err)
return foo, dir, bar
}
func (t *cachingFSTest) statFiles(
f, g, h *os.File) (foo, dir, bar os.FileInfo) {
var err error
foo, err = f.Stat()
AssertEq(nil, err)
dir, err = g.Stat()
AssertEq(nil, err)
bar, err = h.Stat()
AssertEq(nil, err)
return foo, dir, bar
}
func getInodeID(fi os.FileInfo) uint64 {
return fi.Sys().(*syscall.Stat_t).Ino
}
////////////////////////////////////////////////////////////////////////
// Basics
////////////////////////////////////////////////////////////////////////
type BasicsTest struct {
cachingFSTest
}
var _ SetUpInterface = &BasicsTest{}
func init() { RegisterTestSuite(&BasicsTest{}) }
func (t *BasicsTest) SetUp(ti *TestInfo) {
const (
lookupEntryTimeout = 0
getattrTimeout = 0
)
t.cachingFSTest.setUp(ti, lookupEntryTimeout, getattrTimeout)
}
func (t *BasicsTest) StatNonexistent() {
names := []string{
"blah",
"bar",
"dir/blah",
"dir/dir",
"dir/foo",
}
for _, n := range names {
_, err := os.Stat(path.Join(t.Dir, n))
AssertNe(nil, err)
ExpectTrue(os.IsNotExist(err), "n: %s, err: %v", n, err)
}
}
func (t *BasicsTest) StatFoo() {
fi, err := os.Stat(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
ExpectEq("foo", fi.Name())
ExpectEq(cachingfs.FooSize, fi.Size())
ExpectEq(0777, fi.Mode())
ExpectThat(fi.ModTime(), timeutil.TimeEq(t.initialMtime))
ExpectFalse(fi.IsDir())
ExpectEq(t.fs.FooID(), getInodeID(fi))
ExpectEq(1, fi.Sys().(*syscall.Stat_t).Nlink)
}
func (t *BasicsTest) StatDir() {
fi, err := os.Stat(path.Join(t.Dir, "dir"))
AssertEq(nil, err)
ExpectEq("dir", fi.Name())
ExpectEq(os.ModeDir|0777, fi.Mode())
ExpectThat(fi.ModTime(), timeutil.TimeEq(t.initialMtime))
ExpectTrue(fi.IsDir())
ExpectEq(t.fs.DirID(), getInodeID(fi))
ExpectEq(1, fi.Sys().(*syscall.Stat_t).Nlink)
}
func (t *BasicsTest) StatBar() {
fi, err := os.Stat(path.Join(t.Dir, "dir/bar"))
AssertEq(nil, err)
ExpectEq("bar", fi.Name())
ExpectEq(cachingfs.BarSize, fi.Size())
ExpectEq(0777, fi.Mode())
ExpectThat(fi.ModTime(), timeutil.TimeEq(t.initialMtime))
ExpectFalse(fi.IsDir())
ExpectEq(t.fs.BarID(), getInodeID(fi))
ExpectEq(1, fi.Sys().(*syscall.Stat_t).Nlink)
}
////////////////////////////////////////////////////////////////////////
// No caching
////////////////////////////////////////////////////////////////////////
type NoCachingTest struct {
cachingFSTest
}
var _ SetUpInterface = &NoCachingTest{}
func init() { RegisterTestSuite(&NoCachingTest{}) }
func (t *NoCachingTest) SetUp(ti *TestInfo) {
const (
lookupEntryTimeout = 0
getattrTimeout = 0
)
t.cachingFSTest.setUp(ti, lookupEntryTimeout, getattrTimeout)
}
func (t *NoCachingTest) StatStat() {
fooBefore, dirBefore, barBefore := t.statAll()
fooAfter, dirAfter, barAfter := t.statAll()
// Make sure everything matches.
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(fooBefore.ModTime()))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(dirBefore.ModTime()))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(barBefore.ModTime()))
ExpectEq(getInodeID(fooBefore), getInodeID(fooAfter))
ExpectEq(getInodeID(dirBefore), getInodeID(dirAfter))
ExpectEq(getInodeID(barBefore), getInodeID(barAfter))
}
func (t *NoCachingTest) StatRenumberStat() {
t.statAll()
t.fs.RenumberInodes()
fooAfter, dirAfter, barAfter := t.statAll()
// We should see the new inode IDs, because the entries should not have been
// cached.
ExpectEq(t.fs.FooID(), getInodeID(fooAfter))
ExpectEq(t.fs.DirID(), getInodeID(dirAfter))
ExpectEq(t.fs.BarID(), getInodeID(barAfter))
}
func (t *NoCachingTest) StatMtimeStat() {
newMtime := t.initialMtime.Add(time.Second)
t.statAll()
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statAll()
// We should see the new mtimes, because the attributes should not have been
// cached.
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
}
func (t *NoCachingTest) StatRenumberMtimeStat() {
newMtime := t.initialMtime.Add(time.Second)
t.statAll()
t.fs.RenumberInodes()
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statAll()
// We should see the new inode IDs and mtimes, because nothing should have
// been cached.
ExpectEq(t.fs.FooID(), getInodeID(fooAfter))
ExpectEq(t.fs.DirID(), getInodeID(dirAfter))
ExpectEq(t.fs.BarID(), getInodeID(barAfter))
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
}
////////////////////////////////////////////////////////////////////////
// Entry caching
////////////////////////////////////////////////////////////////////////
type EntryCachingTest struct {
cachingFSTest
lookupEntryTimeout time.Duration
}
var _ SetUpInterface = &EntryCachingTest{}
func init() { RegisterTestSuite(&EntryCachingTest{}) }
func (t *EntryCachingTest) SetUp(ti *TestInfo) {
t.lookupEntryTimeout = 250 * time.Millisecond
t.SampleTest.MountConfig.EnableVnodeCaching = true
t.cachingFSTest.setUp(ti, t.lookupEntryTimeout, 0)
}
func (t *EntryCachingTest) StatStat() {
fooBefore, dirBefore, barBefore := t.statAll()
fooAfter, dirAfter, barAfter := t.statAll()
// Make sure everything matches.
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(fooBefore.ModTime()))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(dirBefore.ModTime()))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(barBefore.ModTime()))
ExpectEq(getInodeID(fooBefore), getInodeID(fooAfter))
ExpectEq(getInodeID(dirBefore), getInodeID(dirAfter))
ExpectEq(getInodeID(barBefore), getInodeID(barAfter))
}
func (t *EntryCachingTest) StatRenumberStat() {
fooBefore, dirBefore, barBefore := t.statAll()
t.fs.RenumberInodes()
fooAfter, dirAfter, barAfter := t.statAll()
// We should still see the old inode IDs, because the inode entries should
// have been cached.
ExpectEq(getInodeID(fooBefore), getInodeID(fooAfter))
ExpectEq(getInodeID(dirBefore), getInodeID(dirAfter))
ExpectEq(getInodeID(barBefore), getInodeID(barAfter))
// But after waiting for the entry cache to expire, we should see the new
// IDs.
//
// Note that the cache is not guaranteed to expire on darwin. See notes on
// fuse.MountConfig.EnableVnodeCaching.
if runtime.GOOS != "darwin" {
time.Sleep(2 * t.lookupEntryTimeout)
fooAfter, dirAfter, barAfter = t.statAll()
ExpectEq(t.fs.FooID(), getInodeID(fooAfter))
ExpectEq(t.fs.DirID(), getInodeID(dirAfter))
ExpectEq(t.fs.BarID(), getInodeID(barAfter))
}
}
func (t *EntryCachingTest) StatMtimeStat() {
newMtime := t.initialMtime.Add(time.Second)
t.statAll()
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statAll()
// We should see the new mtimes, because the attributes should not have been
// cached.
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
}
func (t *EntryCachingTest) StatRenumberMtimeStat() {
newMtime := t.initialMtime.Add(time.Second)
fooBefore, dirBefore, barBefore := t.statAll()
t.fs.RenumberInodes()
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statAll()
// We should still see the old inode IDs, because the inode entries should
// have been cached. But the attributes should not have been.
ExpectEq(getInodeID(fooBefore), getInodeID(fooAfter))
ExpectEq(getInodeID(dirBefore), getInodeID(dirAfter))
ExpectEq(getInodeID(barBefore), getInodeID(barAfter))
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
// After waiting for the entry cache to expire, we should see fresh
// everything.
//
// Note that the cache is not guaranteed to expire on darwin. See notes on
// fuse.MountConfig.EnableVnodeCaching.
if runtime.GOOS != "darwin" {
time.Sleep(2 * t.lookupEntryTimeout)
fooAfter, dirAfter, barAfter = t.statAll()
ExpectEq(t.fs.FooID(), getInodeID(fooAfter))
ExpectEq(t.fs.DirID(), getInodeID(dirAfter))
ExpectEq(t.fs.BarID(), getInodeID(barAfter))
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
}
}
////////////////////////////////////////////////////////////////////////
// Attribute caching
////////////////////////////////////////////////////////////////////////
type AttributeCachingTest struct {
cachingFSTest
getattrTimeout time.Duration
}
var _ SetUpInterface = &AttributeCachingTest{}
func init() { RegisterTestSuite(&AttributeCachingTest{}) }
func (t *AttributeCachingTest) SetUp(ti *TestInfo) {
t.getattrTimeout = 250 * time.Millisecond
t.cachingFSTest.setUp(ti, 0, t.getattrTimeout)
}
func (t *AttributeCachingTest) StatStat() {
fooBefore, dirBefore, barBefore := t.statAll()
fooAfter, dirAfter, barAfter := t.statAll()
// Make sure everything matches.
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(fooBefore.ModTime()))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(dirBefore.ModTime()))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(barBefore.ModTime()))
ExpectEq(getInodeID(fooBefore), getInodeID(fooAfter))
ExpectEq(getInodeID(dirBefore), getInodeID(dirAfter))
ExpectEq(getInodeID(barBefore), getInodeID(barAfter))
}
func (t *AttributeCachingTest) StatRenumberStat() {
t.statAll()
t.fs.RenumberInodes()
fooAfter, dirAfter, barAfter := t.statAll()
// We should see the new inode IDs, because the entries should not have been
// cached.
ExpectEq(t.fs.FooID(), getInodeID(fooAfter))
ExpectEq(t.fs.DirID(), getInodeID(dirAfter))
ExpectEq(t.fs.BarID(), getInodeID(barAfter))
}
func (t *AttributeCachingTest) StatMtimeStat_ViaPath() {
newMtime := t.initialMtime.Add(time.Second)
t.statAll()
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statAll()
// Since we don't have entry caching enabled, the call above had to look up
// the entry again. With the lookup we returned new attributes, so it's
// possible that the mtime will be fresh. On Linux it appears to be, and on
// OS X it appears to not be.
m := AnyOf(timeutil.TimeEq(newMtime), timeutil.TimeEq(t.initialMtime))
ExpectThat(fooAfter.ModTime(), m)
ExpectThat(dirAfter.ModTime(), m)
ExpectThat(barAfter.ModTime(), m)
}
func (t *AttributeCachingTest) StatMtimeStat_ViaFileDescriptor() {
newMtime := t.initialMtime.Add(time.Second)
// Open everything, fixing a particular inode number for each.
foo, dir, bar := t.openFiles()
defer func() {
foo.Close()
dir.Close()
bar.Close()
}()
fooBefore, dirBefore, barBefore := t.statFiles(foo, dir, bar)
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statFiles(foo, dir, bar)
// We should still see the old cached mtime.
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(fooBefore.ModTime()))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(dirBefore.ModTime()))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(barBefore.ModTime()))
// After waiting for the attribute cache to expire, we should see the fresh
// mtime.
time.Sleep(2 * t.getattrTimeout)
fooAfter, dirAfter, barAfter = t.statFiles(foo, dir, bar)
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
}
func (t *AttributeCachingTest) StatRenumberMtimeStat_ViaPath() {
newMtime := t.initialMtime.Add(time.Second)
t.statAll()
t.fs.RenumberInodes()
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statAll()
// We should see new everything, because this is the first time the new
// inodes have been encountered. Entries for the old ones should not have
// been cached, because we have entry caching disabled.
ExpectEq(t.fs.FooID(), getInodeID(fooAfter))
ExpectEq(t.fs.DirID(), getInodeID(dirAfter))
ExpectEq(t.fs.BarID(), getInodeID(barAfter))
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
}
func (t *AttributeCachingTest) StatRenumberMtimeStat_ViaFileDescriptor() {
newMtime := t.initialMtime.Add(time.Second)
// Open everything, fixing a particular inode number for each.
foo, dir, bar := t.openFiles()
defer func() {
foo.Close()
dir.Close()
bar.Close()
}()
fooBefore, dirBefore, barBefore := t.statFiles(foo, dir, bar)
t.fs.RenumberInodes()
t.fs.SetMtime(newMtime)
fooAfter, dirAfter, barAfter := t.statFiles(foo, dir, bar)
// We should still see the old cached mtime with the old inode ID.
ExpectEq(getInodeID(fooBefore), getInodeID(fooAfter))
ExpectEq(getInodeID(dirBefore), getInodeID(dirAfter))
ExpectEq(getInodeID(barBefore), getInodeID(barAfter))
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(fooBefore.ModTime()))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(dirBefore.ModTime()))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(barBefore.ModTime()))
// After waiting for the attribute cache to expire, we should see the fresh
// mtime, still with the old inode ID.
time.Sleep(2 * t.getattrTimeout)
fooAfter, dirAfter, barAfter = t.statFiles(foo, dir, bar)
ExpectEq(getInodeID(fooBefore), getInodeID(fooAfter))
ExpectEq(getInodeID(dirBefore), getInodeID(dirAfter))
ExpectEq(getInodeID(barBefore), getInodeID(barAfter))
ExpectThat(fooAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(dirAfter.ModTime(), timeutil.TimeEq(newMtime))
ExpectThat(barAfter.ModTime(), timeutil.TimeEq(newMtime))
}
////////////////////////////////////////////////////////////////////////
// Page cache
////////////////////////////////////////////////////////////////////////
type PageCacheTest struct {
cachingFSTest
}
var _ SetUpInterface = &PageCacheTest{}
func init() { RegisterTestSuite(&PageCacheTest{}) }
func (t *PageCacheTest) SetUp(ti *TestInfo) {
const (
lookupEntryTimeout = 0
getattrTimeout = 0
)
t.cachingFSTest.setUp(ti, lookupEntryTimeout, getattrTimeout)
}
func (t *PageCacheTest) SingleFileHandle_NoKeepCache() {
t.fs.SetKeepCache(false)
// Open the file.
f, err := os.Open(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
defer f.Close()
// Read its contents once.
f.Seek(0, 0)
AssertEq(nil, err)
c1, err := ioutil.ReadAll(f)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c1))
// And again.
f.Seek(0, 0)
AssertEq(nil, err)
c2, err := ioutil.ReadAll(f)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c2))
// We should have seen the same contents each time.
ExpectTrue(bytes.Equal(c1, c2))
}
func (t *PageCacheTest) SingleFileHandle_KeepCache() {
t.fs.SetKeepCache(true)
// Open the file.
f, err := os.Open(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
defer f.Close()
// Read its contents once.
f.Seek(0, 0)
AssertEq(nil, err)
c1, err := ioutil.ReadAll(f)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c1))
// And again.
f.Seek(0, 0)
AssertEq(nil, err)
c2, err := ioutil.ReadAll(f)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c2))
// We should have seen the same contents each time.
ExpectTrue(bytes.Equal(c1, c2))
}
func (t *PageCacheTest) TwoFileHandles_NoKeepCache() {
t.fs.SetKeepCache(false)
// SetKeepCache(false) doesn't work on OS X. See the notes on
// OpenFileOp.KeepPageCache.
if runtime.GOOS == "darwin" {
return
}
// Open the file.
f1, err := os.Open(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
defer f1.Close()
// Read its contents once.
f1.Seek(0, 0)
AssertEq(nil, err)
c1, err := ioutil.ReadAll(f1)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c1))
// Open a second handle.
f2, err := os.Open(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
defer f2.Close()
// We should see different contents if we read from that handle, due to the
// cache being invalidated at the time of opening.
f2.Seek(0, 0)
AssertEq(nil, err)
c2, err := ioutil.ReadAll(f2)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c2))
ExpectFalse(bytes.Equal(c1, c2))
// Another read from the second handle should give the same result as the
// first one from that handle.
f2.Seek(0, 0)
AssertEq(nil, err)
c3, err := ioutil.ReadAll(f2)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c3))
ExpectTrue(bytes.Equal(c2, c3))
// And another read from the first handle should give the same result yet
// again.
f1.Seek(0, 0)
AssertEq(nil, err)
c4, err := ioutil.ReadAll(f1)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c4))
ExpectTrue(bytes.Equal(c2, c4))
}
func (t *PageCacheTest) TwoFileHandles_KeepCache() {
t.fs.SetKeepCache(true)
// Open the file.
f1, err := os.Open(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
defer f1.Close()
// Read its contents once.
f1.Seek(0, 0)
AssertEq(nil, err)
c1, err := ioutil.ReadAll(f1)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c1))
// Open a second handle.
f2, err := os.Open(path.Join(t.Dir, "foo"))
AssertEq(nil, err)
defer f2.Close()
// We should see the same contents when we read via the second handle.
f2.Seek(0, 0)
AssertEq(nil, err)
c2, err := ioutil.ReadAll(f2)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c2))
ExpectTrue(bytes.Equal(c1, c2))
// Ditto if we read again from the first.
f1.Seek(0, 0)
AssertEq(nil, err)
c3, err := ioutil.ReadAll(f1)
AssertEq(nil, err)
AssertEq(cachingfs.FooSize, len(c3))
ExpectTrue(bytes.Equal(c1, c3))
}