USB passthrough to KVM guest instance

Bogdan Stoica

Linux SysAdmin & DevOps

USB passthrough to KVM guest instance

Jun 18, 2020

LINUX
VIRTUALIZATION

USB passthrough to a KVM guest instance - Main server running: CentOS 7.7 x64 latest version. KVM guest machine running RHEL-7.4 (Maipo) but it can be any linux flavor.

USB flash drive attached to the main server USB port.

I tried all the guides that I could find on internet and even contacted RedHat regarding this. I was not able to expose the USB flash drive to the KVM guest instance.

In the end, in order to do that, the steps bellow are to be performed:

Connect via SSH to the compute node where the USB stick is attached:

 ssh root@main-server-ip

Issue a lsscsi command (the output will be something like the one bellow):

 [root@9ef082b846664b2cb2b36246eb2c29e6 ~]# lsscsi
 [6:0:0:0]    disk    ATA      SSDSC2KB240G8L  LX35  /dev/sda
 [7:0:0:0]    disk    ATA      SSDSC2KB240G8L  LX35  /dev/sdb
 [14:0:0:0]  disk    SCST_BIO 9eee7d60-4761-41 340  /dev/sde
 [15:0:0:0]  disk    SCST_BIO 9eee7d60-4761-41 340  /dev/sdd
 [16:0:0:0]  disk    SCST_BIO 9eee7d60-4761-41 340  /dev/sdg
 [17:0:0:0]  disk    SCST_BIO 9eee7d60-4761-41 340  /dev/sdf
 [18:0:0:0]  disk    SCST_BIO 4b97b991-caf7-4a 340  /dev/sdh
 [19:0:0:0]  disk    SCST_BIO 4b97b991-caf7-4a 340  /dev/sdi
 [20:0:0:0]  disk    SCST_BIO 4b97b991-caf7-4a 340  /dev/sdk
 [21:0:0:0]  disk    SCST_BIO 4b97b991-caf7-4a 340  /dev/sdj
 [24:0:0:0]  disk    SMI      USB DISK        1100  /dev/sdc

In this case, the USB drive is: [24:0:0:0] disk SMI USB DISK 1100 /dev/sdc

Create a xml file to define some USB parameters that will be used to attach the USB device to the running vm (with the following content):

 <hostdev mode='subsystem' type='scsi' managed='no'>
   <source>
 	<adapter name='scsi_host24'/>
 	<address bus='0' target='0' unit='0'/>
   </source>
   <alias name='hostdev0'/>
   <address type='drive' controller='0' bus='0' target='1' unit='0'/>
 </hostdev>

Check the ID of the running kvm guest:

 [root@9ef082b846664b2cb2b36246eb2c29e6 ~]# virsh list

You will get a list with all the running instances on that node. In my case the output is something like this:

 rhel7-usb    e4a91527-a663-486d-bd25-ca69173e8176    running    10.10.10.100/b4:d1:35:00:11:5e    1

Attach the USB device to the kvm guest instance

 virsh attach-device e4a91527-a663-486d-bd25-ca69173e8176 --file scsi.xml

At the end you should see a message like: Device attached successfully

Now if you go to that kvm guest instance you should be able to see the USB drive and use it.