Disconnecting EFI drivers

This is notes that might help with debugging issues possibly caused by EFI drivers

• Create a disk image with a FAT32 filesystem with UEFI full shell, saved as \EFI\Boot\BootX64.efi
• And something to test the scenario with, (we will assume ipxe.efi, but change for your scenario) and save it as /ipxe.efi on the disk
• Boot the troublesome hardware with the just created disk image
• You should get to a UEFI shell prompt. If you then type fs0: and ls you should see your FAT filesystem with ipxe.efi
• If not use map to find different fsX: and try them until you find your filesystem.
• Reproduce the issue by running ipxe.efi

Get in to the shell again

• use drivers -b and devices -b to see a list of handles complete with some kind of textual description

-b is used to get one screen of text at a time

• Find something plausible, try running disconnect <handle>
• where <handle> is the 2- or 3-digit hex value of the handle
• and then retry running ipxe.efi (from the shell, without rebooting first)

With Hyper-V as an example we might look for something like: “Hyper-V”, “VMBus”, “VmbusDxe”, “NetVSC”, “RNDIS”, etc

And then looking at devices for where this is connected to, and try to disconnect it from there

• Most efi shell commands supports -b to get paged output
• Most of the time the output is also available on any connected serial port.
• Or pipe output to a file such as drivers > drivers.txt and then use the editor with edit drivers.txt to show it (this requires a writable filesystem)