Re: [Xen-devel] [v5][PATCH 03/10] xen:x86: define a new hypercall to get RMRR mappings

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 02.09.14 at 11:59, <tiejun.chen@xxxxxxxxx> wrote:
> So could you take a look at the follows?

I'm sorry, but this is a nightmare. Do you know what the term
"callback" means?

> Then when call the hypercall,
> 
> +    case XENMEM_reserved_device_memory_map:
> +    {
> +        struct xen_mem_reserved_device_memory *xmrdm = NULL;
> +        struct xen_mem_reserved_device_memory_map xmrdmm;
> +        XEN_GUEST_HANDLE(xen_mem_reserved_device_memory_t) buffer;
> +        XEN_GUEST_HANDLE_PARAM(xen_mem_reserved_device_memory_t) 
> buffer_param;
> +        const struct iommu_ops *ops = iommu_get_ops();
> +        unsigned int nr_entries = 0;
> +        unsigned int i = 0;
> +
> +        xmrdm = ops->get_device_reserved_memory(&nr_entries);
> +        if ( !nr_entries )
> +            return -ENOENT;
> +        if ( nr_entries < 0 )
> +            return -EFAULT;
> +
> +        if ( copy_from_guest(&xmrdmm, arg, 1) )
> +            return -EFAULT;
> +
> +        if ( xmrdmm.nr_entries < nr_entries )
> +        {
> +            xmrdmm.nr_entries = nr_entries;
> +            if ( copy_to_guest(arg, &xmrdmm, 1) )
> +                return -EFAULT;
> +            return -ENOBUFS;
> +        }
> +
> +        buffer_param = guest_handle_cast(xmrdmm.buffer,
> +                                         xen_mem_reserved_device_memory_t);
> +        buffer = guest_handle_from_param(buffer_param,
> +                                         xen_mem_reserved_device_memory_t);
> +        if ( !guest_handle_okay(buffer, xmrdmm.nr_entries) )
> +            return -EFAULT;
> +
> +        for ( i = 0; i < nr_entries; i++ )
> +        {
> +            if ( copy_to_guest_offset(buffer, i, xmrdm + i, 1) )
> +                return -EFAULT;
> +        }

The equivalent of this loop would move into the new (abstracted at
the IOMMU level) VT-d function. Out of that loop you'd call the
callback passed from here once per iteration; the called function
would take care of storing the needed information and advancing a
private counter. No memory allocation, and no VT-d specific
knowledge required in generic code.

Jan


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