Re: Changing user-mode interfaces

[Paul Durrant <xadimgnik@xxxxxxxxx>]

Top-posting for the sake of consistency...

I think the stable API is that exported by xencontrol.dll itself. It is 
part of the xeniface package so I consider anything 'underneath' it to 
be unstable.
Owen, how difficult would it be to port to use the DLL rather than using 
the IOCTLs directly?
  Paul

On 29/11/2023 12:00, Owen Smith wrote:
> At XenServer we dont use the xencontrol.dll interface, but do use the 
> IOCTLs directly. I'd prefer to keep the IOCTL parameters fixed for each 
> particular IOCTL, but adding new IOCTLs should be fine (IIRC, there are 
> 'gaps' in the numbering between different codes to facilitate this).
> Owen
>
> On Tue, Nov 28, 2023 at 10:40 AM Rafał Wojdyła 
> <omeg@xxxxxxxxxxxxxxxxxxxxxx <mailto:omeg@xxxxxxxxxxxxxxxxxxxxxx>> wrote:
>     Hello,
>
>     What is the policy on potentially breaking changes in the user-mode
>     interface? I have some additions to the gnttab IOCTL (sharing already
>     existing memory in addition to driver-allocated one) which require
>     changing the xencontrol interface or adding another version similar to
>     how the driver interfaces work.
>
>     Additionally I'd like to change how the bookkeeping of gnttab user
>     requests is done: currently each IOCTL contains a process-unique ID
>     as a
>     part of the input. This ID is managed by xencontrol and that can
>     lead to
>     bugs if a process opens more than one xencontrol handle (IDs will be
>     duplicated, the driver checks for that but the requests will fail).
>
>     I think I was the one who wrote that code in the first place (it has
>     been some time... ;), but it seems like we can just remove the request
>     IDs and xeniface would track gnttab requests by the user-mode
>     address of
>     the shared memory (per-process of course). I don't think it's possible
>     to share the same region twice so that should be fine?
>
>     So since the "new" IOCTL parameters would get rid of the ID parameter
>     (and introduce optional address parameter for memory sharing) I'm
>     wondering what's the best way to do the change -- introducing a new
>     version is probably the safest, but it would be a bit messy. I wonder
>     who else besides us (ITL) even uses this code... :)
>
>     Anyway, what's your thoughts on this?
>
>     -- 
>     Rafał Wojdyła
>     Invisible Things Lab