1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
|
package afero
import (
"os"
"syscall"
"time"
)
// If the cache duration is 0, cache time will be unlimited, i.e. once
// a file is in the layer, the base will never be read again for this file.
//
// For cache times greater than 0, the modification time of a file is
// checked. Note that a lot of file system implementations only allow a
// resolution of a second for timestamps... or as the godoc for os.Chtimes()
// states: "The underlying filesystem may truncate or round the values to a
// less precise time unit."
//
// This caching union will forward all write calls also to the base file
// system first. To prevent writing to the base Fs, wrap it in a read-only
// filter - Note: this will also make the overlay read-only, for writing files
// in the overlay, use the overlay Fs directly, not via the union Fs.
type CacheOnReadFs struct {
base Fs
layer Fs
cacheTime time.Duration
}
func NewCacheOnReadFs(base Fs, layer Fs, cacheTime time.Duration) Fs {
return &CacheOnReadFs{base: base, layer: layer, cacheTime: cacheTime}
}
type cacheState int
const (
// not present in the overlay, unknown if it exists in the base:
cacheMiss cacheState = iota
// present in the overlay and in base, base file is newer:
cacheStale
// present in the overlay - with cache time == 0 it may exist in the base,
// with cacheTime > 0 it exists in the base and is same age or newer in the
// overlay
cacheHit
// happens if someone writes directly to the overlay without
// going through this union
cacheLocal
)
func (u *CacheOnReadFs) cacheStatus(name string) (state cacheState, fi os.FileInfo, err error) {
var lfi, bfi os.FileInfo
lfi, err = u.layer.Stat(name)
if err == nil {
if u.cacheTime == 0 {
return cacheHit, lfi, nil
}
if lfi.ModTime().Add(u.cacheTime).Before(time.Now()) {
bfi, err = u.base.Stat(name)
if err != nil {
return cacheLocal, lfi, nil
}
if bfi.ModTime().After(lfi.ModTime()) {
return cacheStale, bfi, nil
}
}
return cacheHit, lfi, nil
}
if err == syscall.ENOENT {
return cacheMiss, nil, nil
}
var ok bool
if err, ok = err.(*os.PathError); ok {
if err == os.ErrNotExist {
return cacheMiss, nil, nil
}
}
return cacheMiss, nil, err
}
func (u *CacheOnReadFs) copyToLayer(name string) error {
return copyToLayer(u.base, u.layer, name)
}
func (u *CacheOnReadFs) Chtimes(name string, atime, mtime time.Time) error {
st, _, err := u.cacheStatus(name)
if err != nil {
return err
}
switch st {
case cacheLocal:
case cacheHit:
err = u.base.Chtimes(name, atime, mtime)
case cacheStale, cacheMiss:
if err := u.copyToLayer(name); err != nil {
return err
}
err = u.base.Chtimes(name, atime, mtime)
}
if err != nil {
return err
}
return u.layer.Chtimes(name, atime, mtime)
}
func (u *CacheOnReadFs) Chmod(name string, mode os.FileMode) error {
st, _, err := u.cacheStatus(name)
if err != nil {
return err
}
switch st {
case cacheLocal:
case cacheHit:
err = u.base.Chmod(name, mode)
case cacheStale, cacheMiss:
if err := u.copyToLayer(name); err != nil {
return err
}
err = u.base.Chmod(name, mode)
}
if err != nil {
return err
}
return u.layer.Chmod(name, mode)
}
func (u *CacheOnReadFs) Stat(name string) (os.FileInfo, error) {
st, fi, err := u.cacheStatus(name)
if err != nil {
return nil, err
}
switch st {
case cacheMiss:
return u.base.Stat(name)
default: // cacheStale has base, cacheHit and cacheLocal the layer os.FileInfo
return fi, nil
}
}
func (u *CacheOnReadFs) Rename(oldname, newname string) error {
st, _, err := u.cacheStatus(oldname)
if err != nil {
return err
}
switch st {
case cacheLocal:
case cacheHit:
err = u.base.Rename(oldname, newname)
case cacheStale, cacheMiss:
if err := u.copyToLayer(oldname); err != nil {
return err
}
err = u.base.Rename(oldname, newname)
}
if err != nil {
return err
}
return u.layer.Rename(oldname, newname)
}
func (u *CacheOnReadFs) Remove(name string) error {
st, _, err := u.cacheStatus(name)
if err != nil {
return err
}
switch st {
case cacheLocal:
case cacheHit, cacheStale, cacheMiss:
err = u.base.Remove(name)
}
if err != nil {
return err
}
return u.layer.Remove(name)
}
func (u *CacheOnReadFs) RemoveAll(name string) error {
st, _, err := u.cacheStatus(name)
if err != nil {
return err
}
switch st {
case cacheLocal:
case cacheHit, cacheStale, cacheMiss:
err = u.base.RemoveAll(name)
}
if err != nil {
return err
}
return u.layer.RemoveAll(name)
}
func (u *CacheOnReadFs) OpenFile(name string, flag int, perm os.FileMode) (File, error) {
st, _, err := u.cacheStatus(name)
if err != nil {
return nil, err
}
switch st {
case cacheLocal, cacheHit:
default:
if err := u.copyToLayer(name); err != nil {
return nil, err
}
}
if flag&(os.O_WRONLY|syscall.O_RDWR|os.O_APPEND|os.O_CREATE|os.O_TRUNC) != 0 {
bfi, err := u.base.OpenFile(name, flag, perm)
if err != nil {
return nil, err
}
lfi, err := u.layer.OpenFile(name, flag, perm)
if err != nil {
bfi.Close() // oops, what if O_TRUNC was set and file opening in the layer failed...?
return nil, err
}
return &UnionFile{base: bfi, layer: lfi}, nil
}
return u.layer.OpenFile(name, flag, perm)
}
func (u *CacheOnReadFs) Open(name string) (File, error) {
st, fi, err := u.cacheStatus(name)
if err != nil {
return nil, err
}
switch st {
case cacheLocal:
return u.layer.Open(name)
case cacheMiss:
bfi, err := u.base.Stat(name)
if err != nil {
return nil, err
}
if bfi.IsDir() {
return u.base.Open(name)
}
if err := u.copyToLayer(name); err != nil {
return nil, err
}
return u.layer.Open(name)
case cacheStale:
if !fi.IsDir() {
if err := u.copyToLayer(name); err != nil {
return nil, err
}
return u.layer.Open(name)
}
case cacheHit:
if !fi.IsDir() {
return u.layer.Open(name)
}
}
// the dirs from cacheHit, cacheStale fall down here:
bfile, _ := u.base.Open(name)
lfile, err := u.layer.Open(name)
if err != nil && bfile == nil {
return nil, err
}
return &UnionFile{base: bfile, layer: lfile}, nil
}
func (u *CacheOnReadFs) Mkdir(name string, perm os.FileMode) error {
err := u.base.Mkdir(name, perm)
if err != nil {
return err
}
return u.layer.MkdirAll(name, perm) // yes, MkdirAll... we cannot assume it exists in the cache
}
func (u *CacheOnReadFs) Name() string {
return "CacheOnReadFs"
}
func (u *CacheOnReadFs) MkdirAll(name string, perm os.FileMode) error {
err := u.base.MkdirAll(name, perm)
if err != nil {
return err
}
return u.layer.MkdirAll(name, perm)
}
func (u *CacheOnReadFs) Create(name string) (File, error) {
bfh, err := u.base.Create(name)
if err != nil {
return nil, err
}
lfh, err := u.layer.Create(name)
if err != nil {
// oops, see comment about OS_TRUNC above, should we remove? then we have to
// remember if the file did not exist before
bfh.Close()
return nil, err
}
return &UnionFile{base: bfh, layer: lfh}, nil
}
|
