DockerCLI/vendor/github.com/containerd/continuity/syscallx/syscall_windows.go

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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
}