Hi Paul,
Paul Durrant <xadimg...@gmail.com> writes: > 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? Well, it is possible to use relative path, AFAIK, linux-based backends are doing exactly this. But problem is with xenstore_mkdir() function, which requires domain id to correctly set owner when it causes call to set_permissions(). As David said, architecturally it will be better to get rid of xenstore_mkdir() usage, because it is used by legacy backends only. But to do this, someone needs to convert legacy backends to use newer API. I have no capacity to do this right now, so I implemented a contained solution: static int xenstore_read_own_domid(unsigned int *domid) in xen_pvdev.c. I believe, this new function will be removed along with whole xen_pvdev.c when there will be no legacy backends left. -- WBR, Volodymyr
