packer-cn/builder/amazon/chroot/lockfile_unix.go

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// +build !windows
package chroot
import (
"errors"
"os"
"syscall"
)
// See: http://linux.die.net/include/sys/file.h
const LOCK_EX = 2
const LOCK_NB = 4
const LOCK_UN = 8
func lockFile(f *os.File) error {
err := syscall.Flock(int(f.Fd()), LOCK_EX|LOCK_NB)
if err != nil {
errno, ok := err.(syscall.Errno)
if ok && errno == syscall.EWOULDBLOCK {
return errors.New("file already locked")
}
return err
}
return nil
}
func unlockFile(f *os.File) error {
return syscall.Flock(int(f.Fd()), LOCK_UN)
}