Why In DokanDispatchWrite has condition to use irp->userbuffer?

[ylgybbz]

In DokanDispatchWrite, there is code:
...
if (RequestContext->Irp->MdlAddress) {
buffer =
MmGetSystemAddressForMdlNormalSafe(RequestContext->Irp->MdlAddress);
} else {
buffer = RequestContext->Irp->UserBuffer;
}
...

Any Condition will use Irp->UserBuffer? I think the the volDeviceObject->Flags has set DO_DIRECT_IO in DokanMountVolume, maybe it always use mdladdress?

[Liryna]

The Irp->UserBuffer was originially supported by Dokan legacy
192b852 then later DO_DIRECT_IO was added by a815463 and probably comes from
https://github.com/microsoft/Windows-driver-samples/blob/7b0c7e24905cf4cafd33da5737b573696beb66b7/general/event/wdm/event.c#L169-L172

If we had to do something here, I tend to say that we could remove DO_DIRECT_IO but I am also afraid it breaks something I am missing