Re: [PATCH v2 4/6] xen_pvdev: Do not assume Dom0 when creating a directory

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 22 Nov 2023, David Woodhouse wrote:
> On Wed, 2023-11-22 at 15:09 -0800, Stefano Stabellini wrote:
> > On Wed, 22 Nov 2023, David Woodhouse wrote:
> > > On Wed, 2023-11-22 at 14:29 -0800, Stefano Stabellini wrote:
> > > > On Wed, 22 Nov 2023, Paul Durrant wrote:
> > > > > On 21/11/2023 22:10, Volodymyr Babchuk wrote:
> > > > > > From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> > > > > > 
> > > > > > Instead of forcing the owner to domid 0, use XS_PRESERVE_OWNER to
> > > > > > inherit the owner of the directory.
> > > > > 
> > > > > Ah... so that's why the previous patch is there.
> > > > > 
> > > > > This is not the right way to fix it. The QEMU Xen support is 
> > > > > *assuming* that
> > > > > QEMU is either running in, or emulating, dom0. In the emulation case 
> > > > > this is
> > > > > probably fine, but the 'real Xen' case it should be using the correct 
> > > > > domid
> > > > > for node creation. I guess this could either be supplied on the 
> > > > > command line
> > > > > or discerned by reading the local domain 'domid' node.
> > > > 
> > > > yes, it should be passed as command line option to QEMU
> > > 
> > > I'm not sure I like the idea of a command line option for something
> > > which QEMU could discover for itself.
> > 
> > That's fine too. I meant to say "yes, as far as I know the toolstack
> > passes the domid to QEMU as a command line option today".
> 
> The -xen-domid argument on the QEMU command line today is the *guest*
> domain ID, not the domain ID in which QEMU itself is running.
> 
> Or were you thinking of something different?

Ops, you are right and I understand your comment better now. The backend
domid is not on the command line but it should be discoverable (on
xenstore if I remember right).