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/*
Copyright The containerd 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.
*/
package syscallx
import (
"syscall"
"unsafe"
)
type reparseDataBuffer struct {
ReparseTag uint32
ReparseDataLength uint16
Reserved uint16
// GenericReparseBuffer
reparseBuffer byte
}
type mountPointReparseBuffer struct {
SubstituteNameOffset uint16
SubstituteNameLength uint16
PrintNameOffset uint16
PrintNameLength uint16
PathBuffer [1]uint16
}
type symbolicLinkReparseBuffer struct {
SubstituteNameOffset uint16
SubstituteNameLength uint16
PrintNameOffset uint16
PrintNameLength uint16
Flags uint32
PathBuffer [1]uint16
}
const (
_IO_REPARSE_TAG_MOUNT_POINT = 0xA0000003
_SYMLINK_FLAG_RELATIVE = 1
)
// Readlink returns the destination of the named symbolic link.
func Readlink(path string, buf []byte) (n int, err error) {
fd, err := syscall.CreateFile(syscall.StringToUTF16Ptr(path), syscall.GENERIC_READ, 0, nil, syscall.OPEN_EXISTING,
syscall.FILE_FLAG_OPEN_REPARSE_POINT|syscall.FILE_FLAG_BACKUP_SEMANTICS, 0)
if err != nil {
return -1, err
}
defer syscall.CloseHandle(fd)
rdbbuf := make([]byte, syscall.MAXIMUM_REPARSE_DATA_BUFFER_SIZE)
var bytesReturned uint32
err = syscall.DeviceIoControl(fd, syscall.FSCTL_GET_REPARSE_POINT, nil, 0, &rdbbuf[0], uint32(len(rdbbuf)), &bytesReturned, nil)
if err != nil {
return -1, err
}
rdb := (*reparseDataBuffer)(unsafe.Pointer(&rdbbuf[0]))
var s string
switch rdb.ReparseTag {
case syscall.IO_REPARSE_TAG_SYMLINK:
data := (*symbolicLinkReparseBuffer)(unsafe.Pointer(&rdb.reparseBuffer))
p := (*[0xffff]uint16)(unsafe.Pointer(&data.PathBuffer[0]))
s = syscall.UTF16ToString(p[data.SubstituteNameOffset/2 : (data.SubstituteNameOffset+data.SubstituteNameLength)/2])
if data.Flags&_SYMLINK_FLAG_RELATIVE == 0 {
if len(s) >= 4 && s[:4] == `\??\` {
s = s[4:]
switch {
case len(s) >= 2 && s[1] == ':': // \??\C:\foo\bar
// do nothing
case len(s) >= 4 && s[:4] == `UNC\`: // \??\UNC\foo\bar
s = `\\` + s[4:]
default:
// unexpected; do nothing
}
} else {
// unexpected; do nothing
}
}
case _IO_REPARSE_TAG_MOUNT_POINT:
data := (*mountPointReparseBuffer)(unsafe.Pointer(&rdb.reparseBuffer))
p := (*[0xffff]uint16)(unsafe.Pointer(&data.PathBuffer[0]))
s = syscall.UTF16ToString(p[data.SubstituteNameOffset/2 : (data.SubstituteNameOffset+data.SubstituteNameLength)/2])
if len(s) >= 4 && s[:4] == `\??\` { // \??\C:\foo\bar
if len(s) < 48 || s[:11] != `\??\Volume{` {
s = s[4:]
}
} else {
// unexpected; do nothing
}
default:
// the path is not a symlink or junction but another type of reparse
// point
return -1, syscall.ENOENT
}
n = copy(buf, []byte(s))
return n, nil
}
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