snapd/osutil/udev

go-udev

Simple udev implementation in Golang developed from scratch. This library allow to listen and manage Linux-kernel (since version 2.6.10) Netlink messages to user space (ie: NETLINK_KOBJECT_UEVENT).

Like udev you will be able to monitor, display and manage devices plug to the system.

How to

Get sources

go get github.com/pilebones/go-udev

Unit test

go test ./...

Compile

go build

Usage

./go-udev -<mode> [-file=<absolute_path>]

Allowed mode: info or monitor File should contains matcher rules (see: "Advanced usage" section)

Info Mode

Crawl /sys/devices uevent struct to detect plugged devices:

./go-udev -info

Monitor Mode

Handle all kernel message to detect change about plugged or unplugged devices:

./go-udev -monitor

Examples

Example of output when a USB storage is plugged:

2017/10/20 23:47:23 Handle netlink.UEvent{
    Action: "add",
    KObj:   "/devices/pci0000:00/0000:00:14.0/usb1/1-1",
    Env:    {"PRODUCT":"58f/6387/10b", "TYPE":"0/0/0", "BUSNUM":"001", "DEVNUM":"005", "SEQNUM":"2511", "DEVNAME":"bus/usb/001/005", "DEVPATH":"/devices/pci0000:00/0000:00:14.0/usb1/1-1", "SUBSYSTEM":"usb", "MAJOR":"189", "MINOR":"4", "DEVTYPE":"usb_device", "ACTION":"add"},
}
2017/10/20 23:47:23 Handle netlink.UEvent{
    Action: "add",
    KObj:   "/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0",
    Env:    {"SUBSYSTEM":"usb", "TYPE":"0/0/0", "INTERFACE":"8/6/80", "MODALIAS":"usb:v058Fp6387d010Bdc00dsc00dp00ic08isc06ip50in00", "SEQNUM":"2512", "DEVPATH":"/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0", "DEVTYPE":"usb_interface", "PRODUCT":"58f/6387/10b", "ACTION":"add"},
}
2017/10/20 23:47:23 Handle netlink.UEvent{
    Action: "add",
    KObj:   "/module/usb_storage",
    Env:    {"SEQNUM":"2513", "ACTION":"add", "DEVPATH":"/module/usb_storage", "SUBSYSTEM":"module"},
}
[...]

Example of output when a USB storage is unplugged:

[...]
2017/10/20 23:47:29 Handle netlink.UEvent{
    Action: "remove",
    KObj:   "/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0/host4/target4:0:0/4:0:0:0/block/sdb",
    Env:    {"SUBSYSTEM":"block", "MAJOR":"8", "MINOR":"16", "DEVNAME":"sdb", "DEVTYPE":"disk", "SEQNUM":"2543", "ACTION":"remove", "DEVPATH":"/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0/host4/target4:0:0/4:0:0:0/block/sdb"},
}
[...]
2017/10/20 23:47:29 Handle netlink.UEvent{
    Action: "remove",
    KObj:   "/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0",
    Env:    {"ACTION":"remove", "SUBSYSTEM":"usb", "DEVTYPE":"usb_interface", "SEQNUM":"2548", "MODALIAS":"usb:v058Fp6387d010Bdc00dsc00dp00ic08isc06ip50in00", "DEVPATH":"/devices/pci0000:00/0000:00:14.0/usb1/1-1/1-1:1.0", "PRODUCT":"58f/6387/10b", "TYPE":"0/0/0", "INTERFACE":"8/6/80"},
}
2017/10/20 23:47:29 Handle netlink.UEvent{
    Action: "remove",
    KObj:   "/devices/pci0000:00/0000:00:14.0/usb1/1-1",
    Env:    {"PRODUCT":"58f/6387/10b", "TYPE":"0/0/0", "DEVNUM":"005", "SEQNUM":"2549", "ACTION":"remove", "DEVPATH":"/devices/pci0000:00/0000:00:14.0/usb1/1-1", "SUBSYSTEM":"usb", "MAJOR":"189", "MINOR":"4", "DEVNAME":"bus/usb/001/005", "DEVTYPE":"usb_device", "BUSNUM":"001"},
}

Note: To implement your own monitoring system, please see main.go as a simple example.

Advanced usage

Is it possible to filter uevents/devices with a Matcher.

A Matcher is a list of your own rules to match only relevant uevent kernel message (see: matcher.sample).

You could pass this file using for both mode:

./go-udev -file  matcher.sample [...]

Throubleshooting

Don't hesitate to notice if you detect a problem with this tool or library.

Links

• Netlink Manual: http://man7.org/linux/man-pages/man7/netlink.7.html
• Linux source code about:
  • Struct sockaddr_netlink: http://elixir.free-electrons.com/linux/v3.12/source/lib/kobject_uevent.c#L45
  • KObject action: http://elixir.free-electrons.com/linux/v3.12/source/lib/kobject_uevent.c#L45

Documentation

• GoDoc Reference.

License

go-udev is available under the GNU GPL v3 - Clause License.