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// +build windows
/*
* Minio Cloud Storage, (C) 2016, 2017 Minio, 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.
*/
package lock
import (
"fmt"
"os"
"path/filepath"
"syscall"
"unsafe"
)
var (
modkernel32 = syscall.NewLazyDLL("kernel32.dll")
procLockFileEx = modkernel32.NewProc("LockFileEx")
)
const (
// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx
lockFileExclusiveLock = 2
lockFileFailImmediately = 1
// see https://msdn.microsoft.com/en-us/library/windows/desktop/ms681382(v=vs.85).aspx
errLockViolation syscall.Errno = 0x21
)
// lockedOpenFile is an internal function.
func lockedOpenFile(path string, flag int, perm os.FileMode, lockType uint32) (*LockedFile, error) {
f, err := Open(path, flag, perm)
if err != nil {
return nil, err
}
if err = lockFile(syscall.Handle(f.Fd()), lockType); err != nil {
f.Close()
return nil, err
}
st, err := os.Stat(path)
if err != nil {
f.Close()
return nil, err
}
if st.IsDir() {
f.Close()
return nil, &os.PathError{
Op: "open",
Path: path,
Err: syscall.EISDIR,
}
}
return &LockedFile{File: f}, nil
}
// TryLockedOpenFile - tries a new write lock, functionality
// it is similar to LockedOpenFile with with syscall.LOCK_EX
// mode but along with syscall.LOCK_NB such that the function
// doesn't wait forever but instead returns if it cannot
// acquire a write lock.
func TryLockedOpenFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
var lockType uint32 = lockFileFailImmediately | lockFileExclusiveLock
switch flag {
case syscall.O_RDONLY:
// https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-lockfileex
lockType = lockFileFailImmediately | 0 // Set this to enable shared lock and fail immediately.
}
return lockedOpenFile(path, flag, perm, lockType)
}
// LockedOpenFile - initializes a new lock and protects
// the file from concurrent access.
func LockedOpenFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
var lockType uint32 = lockFileExclusiveLock
switch flag {
case syscall.O_RDONLY:
// https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-lockfileex
lockType = 0 // Set this to enable shared lock.
}
return lockedOpenFile(path, flag, perm, lockType)
}
// fixLongPath returns the extended-length (\\?\-prefixed) form of
// path when needed, in order to avoid the default 260 character file
// path limit imposed by Windows. If path is not easily converted to
// the extended-length form (for example, if path is a relative path
// or contains .. elements), or is short enough, fixLongPath returns
// path unmodified.
//
// See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
func fixLongPath(path string) string {
// Do nothing (and don't allocate) if the path is "short".
// Empirically (at least on the Windows Server 2013 builder),
// the kernel is arbitrarily okay with < 248 bytes. That
// matches what the docs above say:
// "When using an API to create a directory, the specified
// path cannot be so long that you cannot append an 8.3 file
// name (that is, the directory name cannot exceed MAX_PATH
// minus 12)." Since MAX_PATH is 260, 260 - 12 = 248.
//
// The MSDN docs appear to say that a normal path that is 248 bytes long
// will work; empirically the path must be less then 248 bytes long.
if len(path) < 248 {
// Don't fix. (This is how Go 1.7 and earlier worked,
// not automatically generating the \\?\ form)
return path
}
// The extended form begins with \\?\, as in
// \\?\c:\windows\foo.txt or \\?\UNC\server\share\foo.txt.
// The extended form disables evaluation of . and .. path
// elements and disables the interpretation of / as equivalent
// to \. The conversion here rewrites / to \ and elides
// . elements as well as trailing or duplicate separators. For
// simplicity it avoids the conversion entirely for relative
// paths or paths containing .. elements. For now,
// \\server\share paths are not converted to
// \\?\UNC\server\share paths because the rules for doing so
// are less well-specified.
if len(path) >= 2 && path[:2] == `\\` {
// Don't canonicalize UNC paths.
return path
}
if !filepath.IsAbs(path) {
// Relative path
return path
}
const prefix = `\\?`
pathbuf := make([]byte, len(prefix)+len(path)+len(`\`))
copy(pathbuf, prefix)
n := len(path)
r, w := 0, len(prefix)
for r < n {
switch {
case os.IsPathSeparator(path[r]):
// empty block
r++
case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
// /./
r++
case r+1 < n && path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
// /../ is currently unhandled
return path
default:
pathbuf[w] = '\\'
w++
for ; r < n && !os.IsPathSeparator(path[r]); r++ {
pathbuf[w] = path[r]
w++
}
}
}
// A drive's root directory needs a trailing \
if w == len(`\\?\c:`) {
pathbuf[w] = '\\'
w++
}
return string(pathbuf[:w])
}
// Open - perm param is ignored, on windows file perms/NT acls
// are not octet combinations. Providing access to NT
// acls is out of scope here.
func Open(path string, flag int, perm os.FileMode) (*os.File, error) {
if path == "" {
return nil, syscall.ERROR_FILE_NOT_FOUND
}
pathp, err := syscall.UTF16PtrFromString(fixLongPath(path))
if err != nil {
return nil, err
}
var access uint32
switch flag {
case syscall.O_RDONLY:
access = syscall.GENERIC_READ
case syscall.O_WRONLY:
access = syscall.GENERIC_WRITE
case syscall.O_RDWR:
fallthrough
case syscall.O_RDWR | syscall.O_CREAT:
fallthrough
case syscall.O_WRONLY | syscall.O_CREAT:
access = syscall.GENERIC_READ | syscall.GENERIC_WRITE
case syscall.O_WRONLY | syscall.O_CREAT | syscall.O_APPEND:
access = syscall.FILE_APPEND_DATA
default:
return nil, fmt.Errorf("Unsupported flag (%d)", flag)
}
var createflag uint32
switch {
case flag&syscall.O_CREAT == syscall.O_CREAT:
createflag = syscall.OPEN_ALWAYS
default:
createflag = syscall.OPEN_EXISTING
}
shareflag := uint32(syscall.FILE_SHARE_READ | syscall.FILE_SHARE_WRITE | syscall.FILE_SHARE_DELETE)
accessAttr := uint32(syscall.FILE_ATTRIBUTE_NORMAL | 0x80000000)
fd, err := syscall.CreateFile(pathp, access, shareflag, nil, createflag, accessAttr, 0)
if err != nil {
return nil, err
}
return os.NewFile(uintptr(fd), path), nil
}
func lockFile(fd syscall.Handle, flags uint32) error {
// https://msdn.microsoft.com/en-us/library/windows/desktop/aa365203(v=vs.85).aspx
if fd == syscall.InvalidHandle {
return nil
}
err := lockFileEx(fd, flags, 1, 0, &syscall.Overlapped{})
if err == nil {
return nil
} else if err.Error() == "The process cannot access the file because another process has locked a portion of the file." {
return ErrAlreadyLocked
} else if err != errLockViolation {
return err
}
return nil
}
func lockFileEx(h syscall.Handle, flags, locklow, lockhigh uint32, ol *syscall.Overlapped) (err error) {
var reserved = uint32(0)
r1, _, e1 := syscall.Syscall6(procLockFileEx.Addr(), 6, uintptr(h), uintptr(flags),
uintptr(reserved), uintptr(locklow), uintptr(lockhigh), uintptr(unsafe.Pointer(ol)))
if r1 == 0 {
if e1 != 0 {
err = error(e1)
} else {
err = syscall.EINVAL
}
}
return
}