mirror of https://github.com/k3s-io/k3s
98 lines
2.5 KiB
Go
98 lines
2.5 KiB
Go
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// Copyright 2016 The etcd Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// +build linux
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package fileutil
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import (
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"fmt"
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"io"
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"os"
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"syscall"
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)
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// This used to call syscall.Flock() but that call fails with EBADF on NFS.
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// An alternative is lockf() which works on NFS but that call lets a process lock
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// the same file twice. Instead, use Linux's non-standard open file descriptor
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// locks which will block if the process already holds the file lock.
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//
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// constants from /usr/include/bits/fcntl-linux.h
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const (
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F_OFD_GETLK = 37
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F_OFD_SETLK = 37
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F_OFD_SETLKW = 38
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)
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var (
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wrlck = syscall.Flock_t{
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Type: syscall.F_WRLCK,
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Whence: int16(io.SeekStart),
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Start: 0,
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Len: 0,
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}
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linuxTryLockFile = flockTryLockFile
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linuxLockFile = flockLockFile
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)
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func init() {
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// use open file descriptor locks if the system supports it
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getlk := syscall.Flock_t{Type: syscall.F_RDLCK}
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if err := syscall.FcntlFlock(0, F_OFD_GETLK, &getlk); err == nil {
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linuxTryLockFile = ofdTryLockFile
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linuxLockFile = ofdLockFile
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}
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}
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func TryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
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return linuxTryLockFile(path, flag, perm)
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}
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func ofdTryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
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f, err := os.OpenFile(path, flag, perm)
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if err != nil {
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return nil, fmt.Errorf("ofdTryLockFile failed to open %q (%v)", path, err)
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}
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flock := wrlck
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if err = syscall.FcntlFlock(f.Fd(), F_OFD_SETLK, &flock); err != nil {
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f.Close()
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if err == syscall.EWOULDBLOCK {
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err = ErrLocked
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}
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return nil, err
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}
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return &LockedFile{f}, nil
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}
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func LockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
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return linuxLockFile(path, flag, perm)
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}
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func ofdLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
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f, err := os.OpenFile(path, flag, perm)
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if err != nil {
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return nil, fmt.Errorf("ofdLockFile failed to open %q (%v)", path, err)
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}
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flock := wrlck
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err = syscall.FcntlFlock(f.Fd(), F_OFD_SETLKW, &flock)
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if err != nil {
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f.Close()
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return nil, err
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}
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return &LockedFile{f}, nil
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}
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