Add and generate custom system calls in golang - windows

Question

I want to add the system call GetDiskFreeSpaceExW to the go systemcalls and extend the currently available syscalls for hcsshim: https://github.com/microsoft/hcsshim/blob/master/zsyscall_windows.go
I saw that there is a way of generating them, but it is still unclear how the syntax will be for adding another DLL and what struct types have to be used.
The current hcs.go which is used to generate the system calls for hcsshim:
// Shim for the Host Compute Service (HCS) to manage Windows Server
// containers and Hyper-V containers.
package hcs
import (
"syscall"
)
//go:generate go run ../../mksyscall_windows.go -output zsyscall_windows.go hcs.go
//sys hcsEnumerateComputeSystems(query string, computeSystems **uint16, result **uint16) (hr error) = vmcompute.HcsEnumerateComputeSystems?
//sys hcsCreateComputeSystem(id string, configuration string, identity syscall.Handle, computeSystem *hcsSystem, result **uint16) (hr error) = vmcompute.HcsCreateComputeSystem?
//sys hcsOpenComputeSystem(id string, computeSystem *hcsSystem, result **uint16) (hr error) = vmcompute.HcsOpenComputeSystem?
//sys hcsCloseComputeSystem(computeSystem hcsSystem) (hr error) = vmcompute.HcsCloseComputeSystem?
//sys hcsStartComputeSystem(computeSystem hcsSystem, options string, result **uint16) (hr error) = vmcompute.HcsStartComputeSystem?
//sys hcsShutdownComputeSystem(computeSystem hcsSystem, options string, result **uint16) (hr error) = vmcompute.HcsShutdownComputeSystem?
//sys hcsTerminateComputeSystem(computeSystem hcsSystem, options string, result **uint16) (hr error) = vmcompute.HcsTerminateComputeSystem?
//sys hcsPauseComputeSystem(computeSystem hcsSystem, options string, result **uint16) (hr error) = vmcompute.HcsPauseComputeSystem?
//sys hcsResumeComputeSystem(computeSystem hcsSystem, options string, result **uint16) (hr error) = vmcompute.HcsResumeComputeSystem?
//sys hcsGetComputeSystemProperties(computeSystem hcsSystem, propertyQuery string, properties **uint16, result **uint16) (hr error) = vmcompute.HcsGetComputeSystemProperties?
//sys hcsModifyComputeSystem(computeSystem hcsSystem, configuration string, result **uint16) (hr error) = vmcompute.HcsModifyComputeSystem?
//sys hcsRegisterComputeSystemCallback(computeSystem hcsSystem, callback uintptr, context uintptr, callbackHandle *hcsCallback) (hr error) = vmcompute.HcsRegisterComputeSystemCallback?
//sys hcsUnregisterComputeSystemCallback(callbackHandle hcsCallback) (hr error) = vmcompute.HcsUnregisterComputeSystemCallback?
//sys hcsCreateProcess(computeSystem hcsSystem, processParameters string, processInformation *hcsProcessInformation, process *hcsProcess, result **uint16) (hr error) = vmcompute.HcsCreateProcess?
//sys hcsOpenProcess(computeSystem hcsSystem, pid uint32, process *hcsProcess, result **uint16) (hr error) = vmcompute.HcsOpenProcess?
//sys hcsCloseProcess(process hcsProcess) (hr error) = vmcompute.HcsCloseProcess?
//sys hcsTerminateProcess(process hcsProcess, result **uint16) (hr error) = vmcompute.HcsTerminateProcess?
//sys hcsSignalProcess(process hcsProcess, options string, result **uint16) (hr error) = vmcompute.HcsSignalProcess?
//sys hcsGetProcessInfo(process hcsProcess, processInformation *hcsProcessInformation, result **uint16) (hr error) = vmcompute.HcsGetProcessInfo?
//sys hcsGetProcessProperties(process hcsProcess, processProperties **uint16, result **uint16) (hr error) = vmcompute.HcsGetProcessProperties?
//sys hcsModifyProcess(process hcsProcess, settings string, result **uint16) (hr error) = vmcompute.HcsModifyProcess?
//sys hcsGetServiceProperties(propertyQuery string, properties **uint16, result **uint16) (hr error) = vmcompute.HcsGetServiceProperties?
//sys hcsRegisterProcessCallback(process hcsProcess, callback uintptr, context uintptr, callbackHandle *hcsCallback) (hr error) = vmcompute.HcsRegisterProcessCallback?
//sys hcsUnregisterProcessCallback(callbackHandle hcsCallback) (hr error) = vmcompute.HcsUnregisterProcessCallback?
//sys hcsGetDiskFreeSpaceExW(string lpDirectoryName, **uint16 lpFreeBytesAvailableToCaller, **uint16 lpTotalNumberOfBytes, **uint16 lpTotalNumberOfFreeBytes) =
type hcsSystem syscall.Handle
type hcsProcess syscall.Handle
type hcsCallback syscall.Handle
type hcsProcessInformation struct {
ProcessId uint32
Reserved uint32
StdInput syscall.Handle
StdOutput syscall.Handle
StdError syscall.Handle
}
As result I want to have an working syscall to obtain disk usage and disk space.

Answer 1

Create a file like this:
//go:generate mkwinsyscall -output zfree.go free.go
//sys getDiskFreeSpace(directoryName string, availableToCaller *int, numberOfBytes *int, numberOfFreeBytes *int) (err error) = GetDiskFreeSpaceExW
package main
func main() {
var availableToCaller, numberOfBytes, numberOfFreeBytes int
getDiskFreeSpace(
`C:\`, &availableToCaller, &numberOfBytes, &numberOfFreeBytes,
)
println("availableToCaller", availableToCaller)
println("numberOfBytes", numberOfBytes)
println("numberOfFreeBytes", numberOfFreeBytes)
}
Then build [1]:
go mod init free
go generate
go mod tidy
go build
Alternatively, you can use the premade wrapper [2], but I prefer mine, as you don't have to worry about the string conversion.
https://github.com/golang/sys/tree/master/windows/mkwinsyscall
https://pkg.go.dev/golang.org/x/sys/windows#GetDiskFreeSpaceEx