Re: GNTTABOP_unmap_grant_ref doc

[Keir Fraser <keir.xen@gmail.com>]

On 29/07/2013 09:42, "Ian Campbell" <Ian.Campbell@citrix.com> wrote:

>>> If it turns out that I have misread the doc, I'll happily send a patch to
>>> improve the text (once I'm sure I understand what it should say...)
>> 
>> From reading the implementation it woudl seem clear that host_addr is
>> actually needed.
> 
> In fact I think you need to pass in whatever you passed to the original
> mapping operation, because op->flags here is not an argument from the
> unmap call but is actually a reference to the original flags used to
> make the mapping. So if you made the mapping with GNTMAP_host_map then
> you need to pass the host_addr on unmap. Likewise if you used
> GNTMAP_device_map then you need to specify dev_bus_addr.
> 
> I've added Keir to the CC since he's the ultimate authority on these
> things.

The documentation is simply vague. GNTTABOP_unmap_grant_ref will only undo
mappings that it is given the address of. If you provide a zero address in
either field, that field is ignored. If you provide only zero addresses,
then GNTTABOP_unmap_grant_ref does no work at all!

But you now worked all this out already of course. ;)

 -- Keir