mirror of https://github.com/k3s-io/k3s
98 lines
2.5 KiB
Go
98 lines
2.5 KiB
Go
// Copyright 2016 The etcd Authors
|
|
//
|
|
// 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.
|
|
|
|
// +build linux
|
|
|
|
package fileutil
|
|
|
|
import (
|
|
"fmt"
|
|
"io"
|
|
"os"
|
|
"syscall"
|
|
)
|
|
|
|
// This used to call syscall.Flock() but that call fails with EBADF on NFS.
|
|
// An alternative is lockf() which works on NFS but that call lets a process lock
|
|
// the same file twice. Instead, use Linux's non-standard open file descriptor
|
|
// locks which will block if the process already holds the file lock.
|
|
//
|
|
// constants from /usr/include/bits/fcntl-linux.h
|
|
const (
|
|
F_OFD_GETLK = 37
|
|
F_OFD_SETLK = 37
|
|
F_OFD_SETLKW = 38
|
|
)
|
|
|
|
var (
|
|
wrlck = syscall.Flock_t{
|
|
Type: syscall.F_WRLCK,
|
|
Whence: int16(io.SeekStart),
|
|
Start: 0,
|
|
Len: 0,
|
|
}
|
|
|
|
linuxTryLockFile = flockTryLockFile
|
|
linuxLockFile = flockLockFile
|
|
)
|
|
|
|
func init() {
|
|
// use open file descriptor locks if the system supports it
|
|
getlk := syscall.Flock_t{Type: syscall.F_RDLCK}
|
|
if err := syscall.FcntlFlock(0, F_OFD_GETLK, &getlk); err == nil {
|
|
linuxTryLockFile = ofdTryLockFile
|
|
linuxLockFile = ofdLockFile
|
|
}
|
|
}
|
|
|
|
func TryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
|
|
return linuxTryLockFile(path, flag, perm)
|
|
}
|
|
|
|
func ofdTryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
|
|
f, err := os.OpenFile(path, flag, perm)
|
|
if err != nil {
|
|
return nil, fmt.Errorf("ofdTryLockFile failed to open %q (%v)", path, err)
|
|
}
|
|
|
|
flock := wrlck
|
|
if err = syscall.FcntlFlock(f.Fd(), F_OFD_SETLK, &flock); err != nil {
|
|
f.Close()
|
|
if err == syscall.EWOULDBLOCK {
|
|
err = ErrLocked
|
|
}
|
|
return nil, err
|
|
}
|
|
return &LockedFile{f}, nil
|
|
}
|
|
|
|
func LockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
|
|
return linuxLockFile(path, flag, perm)
|
|
}
|
|
|
|
func ofdLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
|
|
f, err := os.OpenFile(path, flag, perm)
|
|
if err != nil {
|
|
return nil, fmt.Errorf("ofdLockFile failed to open %q (%v)", path, err)
|
|
}
|
|
|
|
flock := wrlck
|
|
err = syscall.FcntlFlock(f.Fd(), F_OFD_SETLKW, &flock)
|
|
if err != nil {
|
|
f.Close()
|
|
return nil, err
|
|
}
|
|
return &LockedFile{f}, nil
|
|
}
|