How to correctly invoke the GetVolumeInformation WinAPI function in Go, and avoid unexpected errors?

Calling GetVolumeInformation WinAPI Function in Go

This article details an attempt to retrieve the name of a volume using the GetVolumeInformation WinAPI function from Go. However, the initial efforts encountered an unexpected error.

Problem Statement

The issue arose when trying to pass a string buffer as the lpVolumeNameBuffer parameter. The code failed with the error "unexpected fault address 0xffffffffffffffff."

Analysis

The use of unsafe.Pointer to convert the Go string to a pointer to a uint16 array was identified as the cause of the error. In Go, pointers should generally not be manipulated directly without a good understanding of the consequences.

Solution

To resolve this issue, the code was rewritten to create a fixed-size buffer of uint16 characters and pass a pointer to the first element of the buffer as the lpVolumeNameBuffer parameter. This approach ensures that the buffer is properly aligned and avoids the need to use unsafe.Pointer.

Here is the corrected code:

<code class="go">package main

import (
    "fmt"
    "syscall"
)

func main() {
    const RootPathName = `C:\`
    var VolumeNameBuffer = make([]uint16, syscall.MAX_PATH+1)
    var nVolumeNameSize = uint32(len(VolumeNameBuffer))
    var VolumeSerialNumber uint32
    var MaximumComponentLength uint32
    var FileSystemFlags uint32
    var FileSystemNameBuffer = make([]uint16, 255)
    var nFileSystemNameSize uint32 = syscall.MAX_PATH + 1

    kernel32, err := syscall.LoadLibrary("kernel32.dll")
    if err != nil {
        fmt.Println("Error loading kernel32: ", err)
        return
    }

    getVolume, err := syscall.GetProcAddress(kernel32, "GetVolumeInformationW")
    if err != nil {
        fmt.Println("Error getting GetVolumeInformation address: ", err)
        return
    }

    var nargs uintptr = 8
    ret, _, callErr := syscall.Syscall9(uintptr(getVolume),
        nargs,
        uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(RootPathName))),
        uintptr(unsafe.Pointer(&VolumeNameBuffer[0])),
        uintptr(nVolumeNameSize),
        uintptr(unsafe.Pointer(&VolumeSerialNumber)),
        uintptr(unsafe.Pointer(&MaximumComponentLength)),
        uintptr(unsafe.Pointer(&FileSystemFlags)),
        uintptr(unsafe.Pointer(&FileSystemNameBuffer[0])),
        uintptr(nFileSystemNameSize),
        0)

    if ret != 0 {
        fmt.Println("Call succeeded: ", syscall.UTF16ToString(VolumeNameBuffer))
    } else {
        fmt.Println("Call failed: ", callErr)
    }
}</code>

This modified code should successfully retrieve and print the name of the specified volume.

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