110 lines
2.6 KiB
Go
110 lines
2.6 KiB
Go
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package daemon
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import (
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"errors"
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"fmt"
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"os"
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)
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var (
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// ErrWouldBlock indicates on locking pid-file by another process.
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ErrWouldBlock = errors.New("daemon: Resource temporarily unavailable")
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)
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// LockFile wraps *os.File and provide functions for locking of files.
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type LockFile struct {
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*os.File
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}
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// NewLockFile returns a new LockFile with the given File.
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func NewLockFile(file *os.File) *LockFile {
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return &LockFile{file}
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}
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// CreatePidFile opens the named file, applies exclusive lock and writes
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// current process id to file.
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func CreatePidFile(name string, perm os.FileMode) (lock *LockFile, err error) {
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if lock, err = OpenLockFile(name, perm); err != nil {
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return
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}
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if err = lock.Lock(); err != nil {
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lock.Remove()
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return
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}
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if err = lock.WritePid(); err != nil {
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lock.Remove()
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}
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return
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}
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// OpenLockFile opens the named file with flags os.O_RDWR|os.O_CREATE and specified perm.
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// If successful, function returns LockFile for opened file.
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func OpenLockFile(name string, perm os.FileMode) (lock *LockFile, err error) {
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var file *os.File
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if file, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE, perm); err == nil {
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lock = &LockFile{file}
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}
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return
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}
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// Lock apply exclusive lock on an open file. If file already locked, returns error.
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func (file *LockFile) Lock() error {
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return lockFile(file.Fd())
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}
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// Unlock remove exclusive lock on an open file.
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func (file *LockFile) Unlock() error {
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return unlockFile(file.Fd())
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}
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// ReadPidFile reads process id from file with give name and returns pid.
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// If unable read from a file, returns error.
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func ReadPidFile(name string) (pid int, err error) {
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var file *os.File
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if file, err = os.OpenFile(name, os.O_RDONLY, 0640); err != nil {
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return
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}
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defer file.Close()
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lock := &LockFile{file}
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pid, err = lock.ReadPid()
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return
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}
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// WritePid writes current process id to an open file.
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func (file *LockFile) WritePid() (err error) {
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if _, err = file.Seek(0, os.SEEK_SET); err != nil {
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return
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}
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var fileLen int
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if fileLen, err = fmt.Fprint(file, os.Getpid()); err != nil {
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return
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}
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if err = file.Truncate(int64(fileLen)); err != nil {
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return
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}
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err = file.Sync()
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return
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}
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// ReadPid reads process id from file and returns pid.
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// If unable read from a file, returns error.
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func (file *LockFile) ReadPid() (pid int, err error) {
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if _, err = file.Seek(0, os.SEEK_SET); err != nil {
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return
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}
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_, err = fmt.Fscan(file, &pid)
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return
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}
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// Remove removes lock, closes and removes an open file.
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func (file *LockFile) Remove() error {
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defer file.Close()
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if err := file.Unlock(); err != nil {
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return err
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}
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return os.Remove(file.Name())
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}
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