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+# CSI Proxy API Implementation with WMI
+
+
+## Table of Contents
+
+- [Windows Management Instrumentation](#wmi)
+- [microsoft/wmi library](#microsoft-wmi-library)
+- [How to make WMI queries and debug with PowerShell](#debug-powershell)
+
+
+
+## Windows Management Instrumentation
+
+Windows Management Instrumentation (WMI) is the infrastructure for management data and operations on Windows-based operating systems.
+Refer to [WMI start page](https://learn.microsoft.com/en-us/windows/win32/wmisdk/wmi-start-page) for more details.
+
+The purpose of WMI is to define a proprietary set of environment-independent specifications that enable sharing management information between management apps.
+
+CSI-proxy makes WMI queries using `microsoft/wmi` library. Refer to for the call graph below.
+
+
+## microsoft/wmi library
+
+
+
+`microsoft/wmi` library leverages the traditional COM interfaces (`IDispatch`) to call the WMI.
+
+COM interfaces wrap the parameters and return value in a `VARIANT` struct.
+`microsoft/wmi` library converts the `VARIANT` to native Go types and struct.
+
+A typical WMI query may need to obtain a WMI session of the target machine first, which
+can be done by the helper methods `NewWMISession` and `QueryFromWMI` in `pkg/cim`.
+
+A query like `SELECT * FROM MSFT_Volume` may return all the volumes on the current node.
+
+### Queries
+
+The query may return a list of WMI objects of the generic type `cim.WmiInstance`. You may further cast
+the object down to a specific WMI class (e.g. `MSFT_Disk`). You may find the WMI class definition
+from the API doc.
+
+For example, the property `PartitionStyle` on [MSFT_Disk](https://learn.microsoft.com/en-us/windows-hardware/drivers/storage/msft-disk#properties) is defined as
+
+| API constraints | Settings |
+|-----------------|---------------------------------------|
+| Property | PartitionStyle |
+| Data type | UInt16 |
+| Access type | Read-only |
+| Qualifiers | Required |
+| Description | The partition style used by the disk. |
+
+You may use `GetProperty` to get the value of `PartitionStyle` to get the value from the `VARAINT` and
+converts it back to Go types.
+
+```go
+retValue, err := disk.GetProperty("PartitionStyle")
+if err != nil {
+ return false, fmt.Errorf("failed to query partition style of disk %d: %w", diskNumber, err)
+}
+
+partitionStyle = retValue.(int32)
+```
+
+Note that some auto-generated wrapper methods in `microsoft/wmi` may have wrong data types mapping to Go native types.
+It's always recommended to use `GetProperty` instead of these pre-defined wrapper methods.
+
+### Class Method
+
+A WMI class may have some Class Method to call for a specific operation (e.g., creating a new partition).
+
+You may use the method `InvokeMethodWithReturn`.
+
+```go
+result, err := disk.InvokeMethodWithReturn(
+ "CreatePartition",
+ nil, // Size
+ true, // UseMaximumSize
+ nil, // Offset
+ nil, // Alignment
+ nil, // DriveLetter
+ false, // AssignDriveLetter
+ nil, // MbrType,
+ cim.GPTPartitionTypeBasicData, // GPT Type
+ false, // IsHidden
+ false, // IsActive,
+)
+// 42002 is returned by driver letter failed to assign after partition
+if (result != 0 && result != 42002) || err != nil {
+ return fmt.Errorf("error creating partition on disk %d. result: %d, err: %v", diskNumber, result, err)
+}
+```
+
+Both input and output parameters can be found in the [CreatePartition API doc](https://learn.microsoft.com/en-us/windows-hardware/drivers/storage/createpartition-msft-disk).
+
+```c
+UInt32 CreatePartition(
+ [in] UInt64 Size,
+ [in] Boolean UseMaximumSize,
+ [in] UInt64 Offset,
+ [in] UInt32 Alignment,
+ [in] Char16 DriveLetter,
+ [in] Boolean AssignDriveLetter,
+ [in] UInt16 MbrType,
+ [in] String GptType,
+ [in] Boolean IsHidden,
+ [in] Boolean IsActive,
+ [out] String CreatedPartition,
+ [out] String ExtendedStatus
+);
+```
+
+There parameters will be wrapped in `VARIANT` with the corresponding types.
+
+Eventually the method `CreatePartition` on the WMI object will be called via `IDispatch` interface in native COM/OLE calls.
+
+Refer to [CallMethod](https://github.com/go-ole/go-ole/blob/master/oleutil/oleutil.go#L49-L52) if you need to know the details of a COM/OLE call.
+
+```go
+func CallMethod(disp *ole.IDispatch, name string, params ...interface{}) (result *ole.VARIANT, err error) {
+ return disp.InvokeWithOptionalArgs(name, ole.DISPATCH_METHOD, params)
+}
+```
+
+
+## Debug with PowerShell
+
+### How to make WMI call with PowerShell
+
+You will find the `Query` for each method in `pkg/cim` package.
+For example, this is the comment of `ListVolume`
+
+```go
+// ListVolumes retrieves all available volumes on the system.
+//
+// The equivalent WMI query is:
+//
+// SELECT [selectors] FROM MSFT_Volume
+//
+// Refer to https://learn.microsoft.com/en-us/windows-hardware/drivers/storage/msft-volume
+// for the WMI class definition.
+```
+
+You may use the same query with PowerShell cmdlet `Get-CimInstance` targeting
+the corresponding namespace `Root\Microsoft\Windows\Storage`.
+
+The return result will be an object of `MSFT_Volume` WMI class.
+
+e.g. if we're going to list the details of the first volume on Windows system:
+
+```powershell
+PS C:\Users\Administrator> $vol = (Get-CimInstance -Namespace "Root\Microsoft\Windows\Storage" -Query "SELECT * FROM MSFT_Volume")[0]
+PS C:\Users\Administrator> $vol
+
+ObjectId : {1}\\WIN-8E2EVAQ9QSB\root/Microsoft/Windows/Storage/Providers_v2\WSP_Volume.ObjectId=
+"{b65bb3cd-da86-11ee-854b-806e6f6e6963}:VO:\\?\Volume{1781d1eb-2c0a-47ed-987f-c229b9c
+02527}\"
+PassThroughClass :
+PassThroughIds :
+PassThroughNamespace :
+PassThroughServer :
+UniqueId : \\?\Volume{1781d1eb-2c0a-47ed-987f-c229b9c02527}\
+AllocationUnitSize : 4096
+DedupMode : 4
+DriveLetter : C
+DriveType : 3
+FileSystem : NTFS
+FileSystemLabel :
+FileSystemType : 14
+HealthStatus : 1
+OperationalStatus : {53261}
+Path : \\?\Volume{1781d1eb-2c0a-47ed-987f-c229b9c02527}\
+Size : 536198770688
+SizeRemaining : 407553982464
+PSComputerName :
+```
+
+Then you may use `obj.FileSystem` to get the file system of the volume.
+
+```powershell
+PS C:\Users\Administrator> $vol.FileSystem
+NTFS
+```
+
+### Call Class Method
+
+You may get Class Methods for a single CIM class using `$class.CimClassMethods`.
+
+```powershell
+
+PS C:\Users\Administrator> $class = Get-CimClass -ClassName MSFT_StorageSetting -Namespace "Root\Microsoft\Windows\Storage"
+PS C:\Users\Administrator> $class.CimClassMethods
+
+Name ReturnType Parameters Qualifiers
+---- ---------- ---------- ----------
+Get UInt32 {StorageSetting} {implemented, static}
+Set UInt32 {NewDiskPolicy, ScrubPolicy} {implemented, static}
+UpdateHostStorageCache UInt32 {} {implemented, static}
+```
+
+You may use `Invoke-CimMethod` to invoke those static methods on the `CimClass` object.
+
+```powershell
+PS C:\Users\Administrator> Invoke-CimMethod -CimClass $class -MethodName UpdateHostStorageCache @{}
+
+ReturnValue PSComputerName
+----------- --------------
+ 0
+
+```
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