COSMIC USB Tree Applet

A COSMIC panel applet that shows what is plugged into the machine, how it is plugged in, and — the part nothing else on the panel answers — the link speed each device actually negotiated.

What it does

• The real topology. Devices are drawn as the tree they form: each one under the hub it hangs off, in port order, with the tree guides to match. A hub chain looks like a hub chain.
• Negotiated speed, per device. Every row carries the rate its link came up at — 12 Mb/s, 480 Mb/s, 5 Gb/s — not the speed of the port it is in and not the speed printed on the box.
• Slow links called out. A device that supports SuperSpeed but came up at USB 2.0 speeds is behind a slow port, cable or hub. Those rows are marked, and the panel icon turns the theme's warning colour so it is visible without opening the popup.
• What each device is. Class and interface descriptors pick the icon: keyboards, mice, controllers, webcams, storage, network adapters, audio, Bluetooth radios, hubs.
• Live. The kernel multicasts a uevent whenever a device appears or leaves, so the tree updates as it happens rather than on a timer.

How it reads devices

Everything comes from /sys/bus/usb/devices: no daemon, no kernel module, no libusb, no elevated privileges. The kernel already knows what came up at what speed, and reading sysfs cannot disturb a device — no probing, no resets.

Attribute	Used for
speed, rx_lanes, tx_lanes	The negotiated link
version (bcdUSB)	What the device supports, and so whether the link is slow for it
bDeviceClass, bInterfaceClass/Protocol	What kind of device it is
idVendor, idProduct, product, manufacturer	Names and IDs
maxchild	Hub port counts

Hardware that ships with empty product strings — cheap hubs, mostly — is looked up in usb.ids from hwdata, if that file is present. It is optional: without it such a device simply shows its IDs.

One thing that surprises people and is not a bug: a USB 3 hub appears twice, once per bus. The specification requires it to present separate USB 2 and USB 3 hubs, and Linux enumerates them on separate buses. lsusb -t shows the same.

Settings

In the popup, behind the settings disclosure:

Setting	Default
Show hubs	on	Off flattens the tree into a plain device list
Show host controllers	off	The root hub of each bus, one per controller
Show device IDs	on	1234:abcd beneath each device
Flag slow links	on	Mark devices running below what they support
Show count in the panel	on	Attached devices, next to the icon

Requirements

• COSMIC desktop
• Linux (the applet reads sysfs)
• A Rust toolchain and just to build
• hwdata — optional, for naming devices that name themselves poorly

Install

just build-release
sudo just install

To install into a user prefix instead:

just build-release
just install prefix=~/.local

Then add USB Tree to the panel in COSMIC Settings → Desktop → Panel → Configure panel applets.

From a terminal

The tree can be printed without a panel, which is also the quickest way to see what the applet would show:

just dump

Bus 5 root hub                                  480 Mb/s  High-Speed     1d6b:0002  Linux xhci-hcd
└─ USB2.1 Hub                                   480 Mb/s  High-Speed     0bda:5411  Generic
   ├─ USB2.0 Hub                                480 Mb/s  High-Speed     2109:2211  VIA Labs, Inc.
   │  └─ MSI Gaming Controller                   12 Mb/s  Full-Speed     1462:3fa4  MS
   └─ USB2.1 Hub                                480 Mb/s  High-Speed     0bda:5411  Generic
      ├─ Razer Basilisk V3 Pro                   12 Mb/s  Full-Speed     1532:00ab  Razer
      └─ B248Y E                                480 Mb/s  High-Speed     0bda:4cb1  Generic

Licence

GPL-3.0-only.