davidchisnall / qemufwcfg

FreeBSD implementation of a NetBSD-compatible /dev/qemufwcfg device

NetBSD-compatible qemufwcfg device for FreeBSD

NetBSD's guest interface to the QEMU firmware configuration device is made of two parts:

• A kernel component that forwards commands to the device from userspace.
• A FUSE filesystem that exports the read-only virtual filesystem, using the simple kernel interface.

This is a very clean design that minimises the amount of complexity in the kernel.

This repository contains a reimplementation of the NetBSD kernel API (inspired by their code and under the same license) and a copy of the FUSE portion with a Makefile that allows it to build on FreeBSD.

Dependencies

The FUSE filesystem depends on the FUSE libraries to build:

# pkg ins fusefs-libs

Building

Both parts of this build with bmake (the default make on FreeBSD / NetBSD). They are built separately to make it easier to upstream the kernel module to FreeBSD and the FreeBSD-specific changes to NetBSD (and packaging it as a port):

$ mkdir obj
$ make
$ cd mount_qemufwcfg
$ mkdir obj
$ make

You can optionally install by running make install in each directory as root:

# make install
# cd mount_qemufwcfg
# make install BINDIR=/usr/local/sbin

Using

The FUSE filesystem depends on both the kernel module from this repository and the fusefs kernel module that is part of the base system. These can be loaded with kldload:

# kldload fusefs
# kldload ./obj/qemufwcfg.ko

You can enable these at boot after installing by putting the following two lines in /boot/loader.conf:

qemufwcfg_load="YES"
fusefs_load="YES"

If the module has loaded correctly then /dev/qemufwcfg should exist. If not, check dmesg for errors and file issues against this repository.

Once the module has loaded, you can try running the qemu filesystem:

# ./mount_qemufwcfg/obj/mount_qemufwcfg /mnt/qemufwcfg/
# ls -R /mnt/qemufwcfg
bios-geometry	bootorder	etc		vgaroms

/mnt/qemufwcfg/etc:
acpi		boot-fail-wait	ramfb		smbios		table-loader	tpm

/mnt/qemufwcfg/etc/acpi:
rsdp	tables

/mnt/qemufwcfg/etc/smbios:
smbios-anchor	smbios-tables

/mnt/qemufwcfg/etc/tpm:
log

/mnt/qemufwcfg/vgaroms:
vgabios-ramfb.bin

The exact set of files depends on your qemu configuration but you should see some files here. You can add additional files using the -fw_cfg command-line flag to QEMU.