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
|
/*
* SPDX-FileCopyrightText: © Hypermode Inc. <hello@hypermode.com>
* SPDX-License-Identifier: Apache-2.0
*/
package badger
import (
"fmt"
"os"
"path/filepath"
"strings"
"github.com/dgraph-io/badger/v4/y"
)
// directoryLockGuard holds a lock on a directory and a pid file inside. The pid file isn't part
// of the locking mechanism, it's just advisory.
type directoryLockGuard struct {
// File handle on the directory, which we've locked.
f *os.File
// The absolute path to our pid file.
path string
}
// acquireDirectoryLock gets a lock on the directory.
// It will also write our pid to dirPath/pidFileName for convenience.
// readOnly is not supported on Plan 9.
func acquireDirectoryLock(dirPath string, pidFileName string, readOnly bool) (
*directoryLockGuard, error) {
if readOnly {
return nil, ErrPlan9NotSupported
}
// Convert to absolute path so that Release still works even if we do an unbalanced
// chdir in the meantime.
absPidFilePath, err := filepath.Abs(filepath.Join(dirPath, pidFileName))
if err != nil {
return nil, y.Wrap(err, "cannot get absolute path for pid lock file")
}
// If the file was unpacked or created by some other program, it might not
// have the ModeExclusive bit set. Set it before we call OpenFile, so that we
// can be confident that a successful OpenFile implies exclusive use.
//
// OpenFile fails if the file ModeExclusive bit set *and* the file is already open.
// So, if the file is closed when the DB crashed, we're fine. When the process
// that was managing the DB crashes, the OS will close the file for us.
//
// This bit of code is copied from Go's lockedfile internal package:
// https://github.com/golang/go/blob/go1.15rc1/src/cmd/go/internal/lockedfile/lockedfile_plan9.go#L58
if fi, err := os.Stat(absPidFilePath); err == nil {
if fi.Mode()&os.ModeExclusive == 0 {
if err := os.Chmod(absPidFilePath, fi.Mode()|os.ModeExclusive); err != nil {
return nil, y.Wrapf(err, "could not set exclusive mode bit")
}
}
} else if !os.IsNotExist(err) {
return nil, err
}
f, err := os.OpenFile(absPidFilePath, os.O_WRONLY|os.O_TRUNC|os.O_CREATE, 0666|os.ModeExclusive)
if err != nil {
if isLocked(err) {
return nil, y.Wrapf(err,
"Cannot open pid lock file %q. Another process is using this Badger database",
absPidFilePath)
}
return nil, y.Wrapf(err, "Cannot open pid lock file %q", absPidFilePath)
}
if _, err = fmt.Fprintf(f, "%d\n", os.Getpid()); err != nil {
f.Close()
return nil, y.Wrapf(err, "could not write pid")
}
return &directoryLockGuard{f, absPidFilePath}, nil
}
// Release deletes the pid file and releases our lock on the directory.
func (guard *directoryLockGuard) release() error {
// It's important that we remove the pid file first.
err := os.Remove(guard.path)
if closeErr := guard.f.Close(); err == nil {
err = closeErr
}
guard.path = ""
guard.f = nil
return err
}
// openDir opens a directory for syncing.
func openDir(path string) (*os.File, error) { return os.Open(path) }
// When you create or delete a file, you have to ensure the directory entry for the file is synced
// in order to guarantee the file is visible (if the system crashes). (See the man page for fsync,
// or see https://github.com/coreos/etcd/issues/6368 for an example.)
func syncDir(dir string) error {
f, err := openDir(dir)
if err != nil {
return y.Wrapf(err, "While opening directory: %s.", dir)
}
err = f.Sync()
closeErr := f.Close()
if err != nil {
return y.Wrapf(err, "While syncing directory: %s.", dir)
}
return y.Wrapf(closeErr, "While closing directory: %s.", dir)
}
// Opening an exclusive-use file returns an error.
// The expected error strings are:
//
// - "open/create -- file is locked" (cwfs, kfs)
// - "exclusive lock" (fossil)
// - "exclusive use file already open" (ramfs)
//
// See https://github.com/golang/go/blob/go1.15rc1/src/cmd/go/internal/lockedfile/lockedfile_plan9.go#L16
var lockedErrStrings = [...]string{
"file is locked",
"exclusive lock",
"exclusive use file already open",
}
// Even though plan9 doesn't support the Lock/RLock/Unlock functions to
// manipulate already-open files, IsLocked is still meaningful: os.OpenFile
// itself may return errors that indicate that a file with the ModeExclusive bit
// set is already open.
func isLocked(err error) bool {
s := err.Error()
for _, frag := range lockedErrStrings {
if strings.Contains(s, frag) {
return true
}
}
return false
}
|
