Re: [PATCH v2 2/6] xen: backends: touch some XenStore nodes only if device...

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 21/11/2023 22:10, Volodymyr Babchuk wrote:
> was created by QEMU
>
> Xen PV devices in QEMU can be created in two ways: either by QEMU
> itself, if they were passed via command line, or by Xen toolstack. In
> the latter case, QEMU scans XenStore entries and configures devices
> accordingly.
>
> In the second case we don't want QEMU to write/delete front-end
> entries for two reasons: it might have no access to those entries if
> it is running in un-privileged domain and it is just incorrect to
> overwrite entries already provided by Xen toolstack, because toolstack
> manages those nodes. For example, it might read backend- or frontend-
> state to be sure that they are both disconnected and it is safe to
> destroy a domain.
>
> This patch checks presence of xendev->backend to check if Xen PV
> device is acting as a backend (i.e. it was configured by Xen
Technally *all* XenDevice objects are backends.

> toolstack) to decide if it should touch frontend entries in XenStore.
> Also, when we need to remove XenStore entries during device teardown
> only if they weren't created by Xen toolstack. If they were created by
> toolstack, then it is toolstack's job to do proper clean-up.