Re: [PATCH v2 1/2] kvm tools: Fix VHOST_SET_MEM_TABLE failure

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jul 12, 2012 at 11:19:47AM +0300, Avi Kivity wrote:
> On 07/12/2012 05:46 AM, Asias He wrote:
> > On Thu, Jul 12, 2012 at 12:09 AM, Avi Kivity <avi@redhat.com> wrote:
> >> On 07/11/2012 07:08 PM, Asias He wrote:
> >>> VHOST_SET_MEM_TABLE failed: Operation not supported
> >>>
> >>> In vhost_set_memory(), We have
> >>>
> >>>         if (mem.padding)
> >>>                 return -EOPNOTSUPP;
> >>>
> >>> So, we need to zero struct vhost_memory.
> >>>
> >>
> >> Is this due to a change in vhost?
> > 
> > Seems we have this bit in the very beginning (commit 3a4d5c94).
> 
> Okay, so it's a documentation problem.  Michael, where is the
> documentation for vhost-net?

Most fields are documented in include/linux/vhost.h
Yes the approach vhost consistently takes is to require all unused
fields to be zeroed out.

> Note we have to initialize it with memset();

We can also use = {} if we want to avoid naming it.

> presumably when we
> repurpose it the name will change, and anonymous unions are not very
> portable.

Looks like in the new C standard they are :)
I'm not sure what we'll do, exactly, if we need to reuse this padding
for something else, but not breaking build for old userspace
will be a priority.

> -- 
> error compiling committee.c: too many arguments to function
>