Re: [Xen-devel] [PATCH 5/5] xen: Add V4V implementation - padding question

[Ross Philipson <ross.philipson@xxxxxxxxxx>]

On 06/11/2013 01:40 PM, Ross Philipson wrote:
> On 06/11/2013 01:25 PM, Tim Deegan wrote:
> > At 13:10 -0400 on 11 Jun (1370956242), Ross Philipson wrote:
> > > > > > ...
> > > > > > +struct v4v_info
> > > > > > +{
> > > > > > + uint64_t ring_magic;
> > > > > > + uint64_t data_magic;
> > > > > > + evtchn_port_t evtchn;
> > > > > Missing padding at the end?
> > > > ack.
> > > At one point during the review of an earlier version of the V4V patch
> > > set, Jan requested that this pad be added to the v4v_info struct. I
> > > understand the padding in all the other structs but I don't understand
> > > this one. This struct is not included in any other structs and is not
> > > followed by any data.
> > 64-bit Xen would see this as a 24-byte struct, even without explicit
> > padding. That would surprise a 32-bit guest that allocated what it saw
> > as a 20-byte struct for Xen to copy into.
> Ah yes, of course. Thanks for the quick response.
>
> Ross
I guess that means that this struct is unhappy then...

typedef struct v4vtables_rule
{
    v4v_addr_t src;  -- 8b
    v4v_addr_t dst;  -- 8b
    uint32_t accept; -- 4b
} v4vtables_rule_t;


> > Tim.
>
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