Issuing IO to devices

[lundman]

So in ZFS we use ZwCreateFile() and standard ReadFile() to issue IO to disks. This is fairly mundane.

Interesting to note that winbtrfs does nothing of the kind. Looks like he opens device handles, .. and... somethingsomething to issue IO. What are the pro/con there.

[lundman]

It uses IoGetDeviceObjectPointer(&path, FILE_READ_ATTRIBUTES, &FileObject, &DeviceObject); and then only ObDereferenceObject(FileObject); and keep the DeviceObject referenced. The just call IoCallDriver(DeviceObject, ... to issue IO. This does appear to avoid the sharing-mode issue we have already come across.

I am unsure how it locks the device from other things making changes to it while it is "opened".