Re: [PATCH] uio_hv_generic: Bind to FCopy device by default

[Naman Jain <namjain@linux.microsoft.com>]

On 5/25/2026 5:34 PM, Ben Hutchings wrote:
> The Hyper-V kernel-mode fcopy driver was removed in 6.10 and the new
> fcopy daemon requires this uio driver to function.  However, by
> default the driver does not bind to any devices, and must be
> configured through the sysfs "new_id" file.
> 
> Since the FCopy device is now only usable through this driver, add its
> ID to the driver's ID table so that the daemon will work "out of the
> box".
> 
> Signed-off-by: Ben Hutchings <benh@debian.org>
> Fixes: ec314f61e4fc ("Drivers: hv: Remove fcopy driver")
> ---
> --- a/drivers/uio/uio_hv_generic.c
> +++ b/drivers/uio/uio_hv_generic.c
> @@ -395,9 +395,15 @@ hv_uio_remove(struct hv_device *dev)
>   	vmbus_free_ring(dev->channel);
>   }
>   
> +static const struct hv_vmbus_device_id hv_uio_id_table[] = {
> +	{ HV_FCOPY_GUID },
> +	{}
> +};
> +MODULE_DEVICE_TABLE(vmbus, hv_uio_id_table);
> +
>   static struct hv_driver hv_uio_drv = {
>   	.name = "uio_hv_generic",
> -	.id_table = NULL, /* only dynamic id's */
> +	.id_table = hv_uio_id_table,
>   	.probe = hv_uio_probe,
>   	.remove = hv_uio_remove,
>   };

Two things worth considering before applying:

1. Please add Cc: stable@vger.kernel.org or is it that we do not want 
this to be ported to older kernels?
2. Every Hyper-V guest (with UIO_HV_GENERIC enabled) will now have an 
additional auto-bound /dev/uio0 node for FCopy. Anything that hardcodes 
/dev/uio0 (e.g. ad-hoc DPDK scripts that bind a NetVSC NIC via 
uio_hv_generic + new_id) may see its index shift, since FCopy now wins 
uio0 at boot. The fix for such consumers is the same thing DPDK and the 
in-tree daemon already do: resolve uio via 
/sys/bus/vmbus/devices/<guid>/uio/ rather than by number. This is not a 
regression in the patch, but it's a behavior change worth calling out.

Regards,
Naman