8.4 Freeing private context data structures

The private context data structures are freed in the Stop() function of the driver's Driver Binding Protocol. The service typically used to free the private context data structures is FreePool() from the EDK II library MemoryAllocationLib.

Shown below is a generic template for freeing a private context data structure in the Stop()function of the Driver Binding Protocol. This code example shows only a fragment from the Stop() service. Chapter 9 covers the services that are produced by the Driver Binding Protocol in more detail.

Example 118-Free a private context data structure

#include <Uefi.h>
#include <Protocol/DriverBinding.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/MemoryAllocationLib.h>

EFI_STATUS
EFIAPI
    <<DriverName>>DriverBindingStop (
  IN EFI_DRIVER_BINDING_PROTOCOL  *This,
  IN EFI_HANDLE                   ControllerHandle,
  IN UINTN                        NumberOfChildren,
  IN EFI_HANDLE                   *ChildHandleBuffer
  )
{
  EFI_STATUS  Status;
  EFI_<<PROTOCOL_NAME_Pm>>_PROTOCOL * <<ProtocolNamePm>>;
  <<DRIVER_NAME>>_PRIVATE_DATA Private;

  //
  // Look up one of the driver's produced protocols
  //
  Status = gBS->OpenProtocol (
                  ControllerHandle,
                  &gEfi <<ProtocolNamePm>>ProtocolGuid,
                  (VOID **)& <<ProtocolNamePm>>,
                  This->DriverBindingHandle,
                  ControllerHandle,
                  EFI_OPEN_PROTOCOL_GET_PROTOCOL
                  );
  if (EFI_ERROR (Status)) {
    return EFI_UNSUPPORTED;
  }

  //
  // Retrieve the private context data structure from the
  // produced protocol
  //
  Private = <<DRIVER_NAME > _PRIVATE_DATA_FROM_ <<PROTOCOL_NAME_Pm>>_THIS (
                <<ProtocolNamePm>>
                );

  //
  // Free the private context data structure
  //
  FreePool (Private);

  return Status;
}

The following example shows a code fragment from the DiskIoDxe driver in the MdeModulePkg that frees the private context data structure.

Example 119-Disk I/O free of a private context data structure

#include <Uefi.h>
#include <Protocol/DriverBinding.h>
#include <Protocol/DiskIo.h>
#include <Library/UefiBootServicesTableLib.h>
#include <Library/MemoryAllocationLib.h>

EFI_STATUS
EFIAPI
DiskIoDriverBindingStop (
  IN EFI_DRIVER_BINDING_PROTOCOL  *This,
  IN EFI_HANDLE                   ControllerHandle,
  IN UINTN                        NumberOfChildren,
  IN EFI_HANDLE                   *ChildHandleBuffer
  )
{
  EFI_STATUS                      Status;
  EFI_DISK_IO_PROTOCOL            *DiskIo;
  DISK_IO_PRIVATE_DATA            *Private;

  //
  // Get our context back.
  //
  Status = gBS->OpenProtocol (
                  ControllerHandle,
                  &gEfiDiskIoProtocolGuid,
                  (VOID **)&DiskIo,
                  This->DriverBindingHandle,
                  ControllerHandle,
                  EFI_OPEN_PROTOCOL_GET_PROTOCOL
                  );
  if (EFI_ERROR (Status)) {
    return EFI_UNSUPPORTED;
  }
  Private = DISK_IO_PRIVATE_DATA_FROM_THIS (DiskIo);

  FreePool (Private);

  return Status;
}