Re: [Xen-devel] [PATCH RESEND 2/4] qdisk, hw/block/xen_disk: Removal of grant mapping

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 02/06/16 10:57, Paulina Szubarczyk wrote:
> On Thu, 2016-06-02 at 11:41 +0200, Roger Pau Monné wrote:
>> On Tue, May 31, 2016 at 06:44:56AM +0200, Paulina Szubarczyk wrote:
>>> Grant mapping related functions and variables are removed
>>> on behalf of grant copy operation introduced in following commits.
>>
>> As David says, you should not remove this before adding a suitable 
>> replacement, or else you are breaking the build.
>>
>> Also, the grant map and unmap mode should be keep (we can talk about 
>> removing persistent grants support), because there are gnttab devices out 
>> there that only support grant map/unmap, but not grant copy IIRC.
>>
> Ok, so there should be a conditional path in this case, but is there a
> way to check if grant copy is supported? 
> If not it might maybe be checked in run-time for example trying to issue
> grant copy and if it fails for the first time set that it is not
> supported and proceed with grant map?

You can try the IOCTL_GNTDEV_GRANT_COPY with a count of 0 which will
return success (0) if this ioctl is supported.

David

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