Go で Windows ドライブの合計サイズを取得する方法?

import (
    "syscall"
    "unsafe"
    "fmt"
)

func main() {
    kernelDLL, err := syscall.LoadDLL("kernel32.dll")
    if err != nil {
        panic(err)
    }

    getDiskFreeSpaceExW, err := kernelDLL.FindProc("GetDiskFreeSpaceExW")
    if err != nil {
        panic(err)
    }
    
    var free, total, avail int64

    path := "c:\"
    r1, r2, lastErr := getDiskFreeSpaceExW.Call(
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(path))),
        uintptr(unsafe.Pointer(&free)),
        uintptr(unsafe.Pointer(&total)),
        uintptr(unsafe.Pointer(&avail)),
    )

    fmt.Println(r1, r2, lastErr)
    fmt.Println("Free:", free, "Total:", total, "Available:", avail)
}

1 0 Success.
Free: 16795295744 Total: 145545281536 Available: 16795295744