Re: [RFC] /dev/ioasid uAPI proposal

[Jason Wang]

在 2021/6/1 下午1:23, Lu Baolu 写道:
> Hi Jason W,
>
> On 6/1/21 1:08 PM, Jason Wang wrote:
> > > > 2) If yes, what's the reason for not simply use the fd opened from
> > > > /dev/ioas. (This is the question that is not answered) and what 
> > > > happens
> > > > if we call GET_INFO for the ioasid_fd?
> > > > 3) If not, how GET_INFO work?
> > > oh, missed this question in prior reply. Personally, no special reason
> > > yet. But using ID may give us opportunity to customize the management
> > > of the handle. For one, better lookup efficiency by using xarray to
> > > store the allocated IDs. For two, could categorize the allocated IDs
> > > (parent or nested). GET_INFO just works with an input FD and an ID.
> >
> >
> > I'm not sure I get this, for nesting cases you can still make the 
> > child an fd.
> >
> > And a question still, under what case we need to create multiple 
> > ioasids on a single ioasid fd?
>
> One possible situation where multiple IOASIDs per FD could be used is
> that devices with different underlying IOMMU capabilities are sharing a
> single FD. In this case, only devices with consistent underlying IOMMU
> capabilities could be put in an IOASID and multiple IOASIDs per FD could
> be applied.
>
> Though, I still not sure about "multiple IOASID per-FD" vs "multiple
> IOASID FDs" for such case.


Right, that's exactly my question. The latter seems much more easier to 
be understood and implemented.

Thanks


> Best regards,
> baolu