Date: Mon, 05 Jan 2015 15:01 -0500 From: John Baldwin <jhb@freebsd.org> To: arch@freebsd.org Subject: devctl(8): A device control utility Message-ID: <3200196.9ZgXApgRdA@ralph.baldwin.cx>
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For a long time I've wanted a way to administratively manipulate the state of new-bus devices from userland. I think the first use case I wanted was a way to power off the sound controller (and anything else I wasn't using) on my first laptop (a Dell Inspiron 5000e I got back in 2000). Similarly, it would be nice to have a way to handle "ejectable" devices (ACPI has a provision for this, and said laptop had _EJx methods to allow one to swap a CD drive out for a battery in a bay while the laptop was in S3). There are some other use cases that would also be nice such as detaching a driver from a PCI device to decide at runtime that it should be passed through to a bhyve guest (and possibly undoing that to allow a host driver to take it back over). Forcing a rescan of a PCI device can be useful if you are using an FPGA and would like to alter BAR layout/sizes without having to reboot the OS. A way to force resets at runtime might also be useful (e.g. a FLR for a PCI device). A few weeks ago I finally sat down and started on an implementation. It can be found here: https://github.com/bsdjhb/freebsd/compare/devctl Sample commands look like: % devctl disable virtio_pci2 # detaches the driver, but leaves the device's name intact similar to # specifying hint.virtio_pci.2.disabled=1 at boot % devctl enable virtio_pci2 # enables a disabled device, including attaching it % devctl detach uart1 # does a full detach, which means the device is now unnamed % devctl attach \_SB_.PCI0.LPC.UAR1 # attaches an unattached device. A provision is made for recognizing # device addresses via an EVENTHANDLER hook that a bus driver can # install. Currently ACPI handles and pci selectors (ala pciconf) # are recognized via hooks in the ACPI and PCI bus drivers. % devctl set driver foo0 bar # forces the 'foo0' device to use the 'bar' device class and thus # only attach to a driver named 'bar' (assuming that 'bar' will # probe it, this doesn't override device_probe). With some changes # to ppt.c, this would allow one to do 'devctl set driver foo0 ppt' # to detach a host driver and mark a device for PCI passthrough at # runtime. I have not yet implemented a "clear driver" to reset # back to an empty device class. The current version also includes 'suspend' and 'resume' commands which use bus_suspend_child() (recently added by Justin Hibbits) to suspend (and possibly power down) individual devices. Implementation notes: For the kernel <-> userland interface, I chose to use ioctls. The ioctls use a 'struct devreq' structure that is modeled on 'struct ifreq' used for network interface ioctls in that there are a set of common fields and a union of request-specific fields. I would have liked to reuse /dev/devctl for this, but it is a single purpose device intended for use by devd. If I had my druthers, I would probably like to rename /dev/devctl to /dev/devevents or /dev/devnotify or some such and create a new /dev/devctl for these control ioctls. Instead what I've done for now is create a /dev/devctl2 for the new ioctls. There is a thin library (libdevctl) that wraps the /dev/devctl2 ioctls and provides methods like devctl_detach(), etc. The thin library even has a manpage already. The devctl(8) utility is then a thin wrapper around libdevctl (and does not yet have a manpage). Do folks have any feedback? -- John Baldwin
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