On 23 November 2023 11:43:35 GMT, Volodymyr Babchuk <volodymyr_babc...@epam.com> wrote: > >Hi David, > >David Woodhouse <dw...@infradead.org> writes: > >> [[S/MIME Signed Part:Undecided]] >> On Thu, 2023-11-23 at 09:28 +0000, Paul Durrant wrote: >>> On 23/11/2023 00:07, Volodymyr Babchuk wrote: >>> > >>> > Hi, >>> > >>> > Volodymyr Babchuk <volodymyr_babc...@epam.com> writes: >>> > >>> > > Hi Stefano, >>> > > >>> > > Stefano Stabellini <sstabell...@kernel.org> writes: >>> > > >>> > > > 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_tyshche...@epam.com> >>> > > > > > > > > > >>> > > > > > > > > > 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). >>> > > >>> > > Yes, it is just "~/domid". I'll add a function that reads it. >>> > >>> > Just a quick question to QEMU folks: is it better to add a global >>> > variable where we will store own Domain ID or it will be okay to read >>> > domid from Xenstore every time we need it? >>> > >>> > If global variable variant is better, what is proffered place to define >>> > this variable? system/globals.c ? >>> > >>> >>> Actually... is it possible for QEMU just to use a relative path for the >>> backend nodes? That way it won't need to know it's own domid, will it? >> >> That covers some of the use cases, but it may also need to know its own >> domid for other purposes. Including writing the *absolute* path of the >> backend, to a frontend node? > >Is this case possible? As I understand, QEMU writes frontend nodes only >when it emulates Xen, otherwise this done by Xen toolstack. And in case >of Xen emulation, QEMU always assumes role of Domain-0.
No, you can hotplug and unplug devices in QEMU even under real Xen. And if QEMU in a driver domain is given sufficient permission to write to its guest's frontend nodes, it should not need to be in dom0.
