Open Stack

On Tue, 2023-01-03 at 14:54 +0000, Stephen Finucane wrote:
> On Mon, 2022-12-26 at 10:04 +0000, 韩光宇 wrote:
> > Hi, all
> > 
> > I want to ask if openstack support USB passthrough now?
> > 
> > Or if I want the instance to recognize the USB flash drive on the
> > host, do you have any suggestions?
> > 
> > Thanks,
> > Han
> 
> This isn't supported in nova and probably never will be. The closest you can get
> is to passthrough an entire USB controller as suggested by this blog [1], but
> that's really a hack and I 100% would not use it in production.

ya so we have discussed usb passthough supprot a few times and its somethign nova could add but there has
neither been the demand or desire to add it stongly enough in the core team to actully do it.

the shorted path to enableing usb passthoug would likely be to add support to cyborg and then add support for that ot nova.
i am perhaps the most open of the nova cores to supporting usb passthough since i have wanted to add it in the past but
if we were to support it it would have to be similar to howe we support pci passhtough. static provisioning and likely only of
stateless devices which rules out usb falsh drives.

usb gps recivers for precision time stamping was one of the usecause raised in the past which we were somewhat open too
the other was usb programmers/debuggers forh cases when vms where used in industral test and automation workflows.

as stephen said the only way to do it today is to piggyback on pci passthough and passhtough a usb contoller not a single device.

if we were to ever support this in nova directly i would proably extend the pci tracker or support other buses like usb or use the generic
resouce table created for persistent memory to model the devices. in eitehr case we would want this capablity to be placement native from the
start if we added this capablity so it would be more and less work then you might imagine to do this right.
less work if we maintain the requirement for statless devices only (ie no usb flash drives) more if you also need to handel multi tenancy and
move operation include data copying, erasure and or encypetion.

i would not expect this to change in the next few release unless multiple operators provide feedback that this is a broadly deired capablity.
with out a top level generic device api for mutple type of devices (vgpu, usb, pci) that was decoupled form the flaovr or an abstraction like
the cyborg device-profile or pci alias it is hard to see a clean way to model this in our api. that is why enabling it in cyborg and then extneding
nova ot support device profiles with a device type of usb is the simplar solution  form a nova perspecitve but that is non trivial from an operational
perspective as you requrie cyborg to utilise the feature. doing it via a usb_alias in the flavor has all the draw backs of the pci_alias, static
configuration that must match on all compute nodes and futher proliferation of flavor explostion. this is one of the reasons we have not added this in
the past.  the work to do it in the libvirt driver would not be hard but the maintaince and operational overhead of using it for operators is non
trivial.

> 
> Stephen
> 
> [1] https://egallen.com/openstack-usb-passthrough/
> 
>