diff --git a/pkg/fileutil/lock_flock.go b/pkg/fileutil/lock_flock.go new file mode 100644 index 000000000..2da93ace6 --- /dev/null +++ b/pkg/fileutil/lock_flock.go @@ -0,0 +1,49 @@ +// Copyright 2016 CoreOS, Inc. +// +// 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 !windows,!plan9,!solaris + +package fileutil + +import ( + "os" + "syscall" +) + +func flockTryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) { + f, err := os.OpenFile(path, flag, perm) + if err != nil { + return nil, err + } + if err = syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil { + f.Close() + if err == syscall.EWOULDBLOCK { + err = ErrLocked + } + return nil, err + } + return &LockedFile{f}, nil +} + +func flockLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) { + f, err := os.OpenFile(path, flag, perm) + if err != nil { + return nil, err + } + if err = syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil { + f.Close() + return nil, err + } + return &LockedFile{f}, err +} diff --git a/pkg/fileutil/lock_linux.go b/pkg/fileutil/lock_linux.go new file mode 100644 index 000000000..6551f575c --- /dev/null +++ b/pkg/fileutil/lock_linux.go @@ -0,0 +1,96 @@ +// Copyright 2016 CoreOS, Inc. +// +// 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 ( + "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(os.SEEK_SET), + 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, 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, err + } + + flock := wrlck + err = syscall.FcntlFlock(f.Fd(), F_OFD_SETLKW, &flock) + + if err != nil { + f.Close() + return nil, err + } + return &LockedFile{f}, err +} diff --git a/pkg/fileutil/lock_unix.go b/pkg/fileutil/lock_unix.go index aa5127ef5..5fc1c8aee 100644 --- a/pkg/fileutil/lock_unix.go +++ b/pkg/fileutil/lock_unix.go @@ -12,38 +12,18 @@ // See the License for the specific language governing permissions and // limitations under the License. -// +build !windows,!plan9,!solaris +// +build !windows,!plan9,!solaris,!linux package fileutil import ( "os" - "syscall" ) func TryLockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) { - f, err := os.OpenFile(path, flag, perm) - if err != nil { - return nil, err - } - if err = syscall.Flock(int(f.Fd()), syscall.LOCK_EX|syscall.LOCK_NB); err != nil { - f.Close() - if err == syscall.EWOULDBLOCK { - err = ErrLocked - } - return nil, err - } - return &LockedFile{f}, nil + return flockTryLockFile(path, flag, perm) } func LockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) { - f, err := os.OpenFile(path, flag, perm) - if err != nil { - return nil, err - } - if err = syscall.Flock(int(f.Fd()), syscall.LOCK_EX); err != nil { - f.Close() - return nil, err - } - return &LockedFile{f}, err + return flockLockFile(path, flag, perm) }