Re: [Xen-devel] [PATCH v3 04/15] argo: init, destroy and soft-reset, with enable command line opt

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Wed, Jan 9, 2019 at 4:35 AM Jan Beulich <JBeulich@xxxxxxxx> wrote:
>
> >>> On 08.01.19 at 23:54, <jandryuk@xxxxxxxxx> wrote:
>
> First of all - please trim your replies.

Sorry.  Will do.

> > On Mon, Jan 7, 2019 at 2:43 AM Christopher Clark 
> > <christopher.w.clark@xxxxxxxxx> wrote:
> >> --- a/docs/misc/xen-command-line.pandoc
> >> +++ b/docs/misc/xen-command-line.pandoc
> >> @@ -182,6 +182,17 @@ Permit Xen to use "Always Running APIC Timer" support 
> >> on compatible hardware
> >>  in combination with cpuidle.  This option is only expected to be useful 
> >> for
> >>  developers wishing Xen to fall back to older timing methods on newer 
> >> hardware.
> >>
> >> +### argo
> >> +> `= <boolean>`
> >> +
> >> +> Default: `false`
> >> +
> >> +Enable the Argo hypervisor-mediated interdomain communication mechanism.
> >> +
> >> +This allows domains access to the Argo hypercall, which supports 
> >> registration
> >> +of memory rings with the hypervisor to receive messages, sending messages 
> >> to
> >> +other domains by hypercall and querying the ring status of other domains.
> >> +
> >
> > Do we want to say it's only available when Xen is compiled with CONFIG_ARGO?
>
> We don't do so elsewhere, so I'm with Christopher.

Okay.

> >> +     */
> >> +    struct argo_ring_info *ring_info;
> >> +    /* domain to be notified when space is available */
> >> +    domid_t domain_id;
> >> +    uint16_t pad;
> >
> > Can we order domain_id after len and drop the pad?
>
> That would still call for a pad field - we prefer to have explicit padding,
> and also to check it's zero, the latter to allow for assigning meaning to
> the field down the road.

This struct is internal to Xen and argo, so do we still need explicit padding?

There are other public argo structs with padding fields.  I haven't
gotten through all the patches, but I think at least some of those are
missing zero checks.

Regards,
Jason

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