How to attach raw disk to lima vm instance? (USB)

[sheerun]

I'd like to flash USB from lima on MacOS, is it possible? Thank you for your time!

[jandubois]

I believe this is not possible, unless something has changed with USB support for qemu on macOS during the last couple of months.

[AkihiroSuda]

I assume the OP is just talking about exposing /Volumes/USBDISKNAME

[jandubois]

I just realized that I have no idea if this would be possible when using the Virtualization.Framework on Ventura, but I suspect it would require additional support in Lima, even if it would be theoretically possible.

[sheerun]

@jandubois Thank you for answering. Could you clarify what was wrong with USB support for qemu driver? Someone reported in this StackOverflow answer its possible, but sudo is needed: https://stackoverflow.com/questions/65816169/how-to-use-usb-with-qemu-on-a-mac-host

As for Virtualization.Framework, maybe using https://gitlab.freedesktop.org/spice/usbredir or porting it to go-lang would be OK workaround? AFAIK there is no official documentation how to do it in Virtualization.Framework? This could also work for QEMU I guess

In principle it should be possible as shown by https://www.virtualhere.com/osx_server_software maybe reverse engineering is an option, but possibly it's not stable API. Or maybe they are using QEMU underneath who knows

[sheerun]

I've just learned there is something like QEMU TCI:

"QEMU TCI (Target-Core-Infrastructure) is a set of Linux kernel modules and userspace libraries that allows QEMU to access storage devices using SCSI commands via the Linux kernel's TCM (Target Core Modules) subsystem. It allows QEMU to act as a SCSI target and provide storage to other systems via SCSI commands.

TCI is a way to expose storage devices to QEMU in a more efficient way than using a file-based image or a block device. This allows QEMU to access storage devices directly, bypassing the file system layer and improving performance.

TCI also provides advanced features such as thin provisioning and snapshots, and it's intended for use cases like storage virtualization, cloud and data center storage, and backup and disaster recovery."

https://github.com/utmapp/UTM is using it to implement USB Sharing (please search for WITH_QEMU_TCI in https://github.com/utmapp/UTM). From what I can read it should be something like -device nec-usb-xhci,id=usb-bus and then they use:

        let maxDevices = input.maximumUsbShare
        let buses = (maxDevices + 2) / 3
        if input.usbBusSupport == .usb3_0 {
            var controller = "qemu-xhci"
            if system.target.rawValue.hasPrefix("pc") || system.target.rawValue.hasPrefix("q35") {
                controller = "nec-usb-xhci"
            }
            for i in 0..<buses {
                f("-device")
                f("\(controller),id=usb-controller-\(i)")
            }
        } else {
            for i in 0..<buses {
                f("-device")
                f("ich9-usb-ehci1,id=usb-controller-\(i)")
                f("-device")
                f("ich9-usb-uhci1,masterbus=usb-controller-\(i).0,firstport=0,multifunction=on")
                f("-device")
                f("ich9-usb-uhci2,masterbus=usb-controller-\(i).0,firstport=2,multifunction=on")
                f("-device")
                f("ich9-usb-uhci3,masterbus=usb-controller-\(i).0,firstport=4,multifunction=on")
            }
        }
        // set up usb forwarding
        for i in 0..<maxDevices {
            f("-chardev")
            f("spicevmc,name=usbredir,id=usbredirchardev\(i)")
            f("-device")
            f("usb-redir,chardev=usbredirchardev\(i),id=usbredirdev\(i),bus=usb-controller-\(i/3).0")
        }

"The nec-usb-xhci device in QEMU is a virtual USB 3.0 host controller that emulates the NEC uPD720201/uPD720202 USB 3.0 host controllers. It is used to provide USB 3.0 support to virtual machines running on QEMU."

Hope it helps!

[jandubois]

I don't know; it looks promising, but have you actually tried it?

I (vaguely) remembered reading UTM issues in the past, like

• USB passthrough does not work in UTM, but is possible with QEMU(?) utmapp/UTM#2439
• Add USB sharing option to macOS guest (from macOS host) utmapp/UTM#3778

and they always look like things should work with UTM, but I only read about people reporting problems with it, not about it working fine for them (to access a storage device, not just a mouse or keyboard).

If you get this working, please leave a message here, or (even better) send a PR to update the README!

[sheerun]

Right, I haven't tried it

[sheerun]

I've sent POC that needs further work: #1317

[AkihiroSuda]

I assume the OP is just talking about exposing /Volumes/USBDISKNAME, and it is already possible without implementing the USB passthrough.

Run limactl edit to edit the yaml:

mounts:
- location: "/Voumes/USBDISKNAME`
  writable: true

https://github.com/lima-vm/lima/blob/v0.14.2/examples/default.yaml#L51

[sheerun]

I'm talking about exposing raw devices e.g. /dev/disk3 => /dev/sda for flashing or interfacing (like Android devices), not attaching already mounted directories

[AkihiroSuda]

Maybe you can run qemu-nbd on the host, and use ssh -R to expose the NBD (Network Block Device) socket to the guest so that it can be interacted with nbd-client

https://www.qemu.org/docs/master/tools/qemu-nbd.html
https://manpages.debian.org/testing/nbd-client/nbd-client.8.en.html

[sheerun]

Thank you for suggestions, but I've already create workaround and anyone who wants in #1317 I don't have time to test other solutions but maybe someone else will. I hope someone will take over #1317 and implement this natively in lima