Re: Grant access to more than one dom

[Daniel De Graaf <dgdegra@tycho.nsa.gov>]

On 05/08/2014 11:47 AM, Simon Martin wrote:
> Hi Daniel.
>
>> I'll  carry on then. When I have it working and tested I'll send it to
>> you  so  you  can  have  a look. Once everyone is happy I'll see about
>> pushing it to a kernel maintainer.
>
> After  being  sidetracked  into  other more boring projects I have now
> almost  completed  this  change,  however  I  have some questions. I'm
> pretty certain that I must be missing something here.
>
> For  the  moment  I  am  only looking at gntalloc.c as it is the one I
> need.
>
> In  the  add_grefs  function  you  create  a couple of list structures
> (queue_gref  and queue_file) and then splice these onto the end of the
> gref_list  and  gntalloc_file_private_data.list lists. However I'm not
> really  sure  what  you  are  doing  here. Can you explain please. The
> problems I see are:
>
> 1.- queue_gref  and queue_file are declared on the stack, however they
> are  then  appended to the lists with no memory allocation whatsoever.
> What are you expecting to happen here?
>
> 2.-  queue_gref   and queue_file are just list structs, i.e. they have
> no  payload,  they  are not part of an encapsulating struct, so again,
> what are you expecting to happen here?
>
> Regards.

The add_grefs function strings the allocated gntalloc_gref structures onto
two linked lists: the list heads are local, but are only used temporarily.
If the operation is successful, the list_splice_tail calls wire up the
linked lists to permanent structures on the heap; if unsuccessful, they
are used to clean up.

-- 
Daniel De Graaf
National Security Agency