> From: Jason Wang > Sent: Tuesday, June 1, 2021 1:30 PM > > 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. > A simple reason discussed in previous thread - there could be 1M's I/O address spaces per device while #FD's are precious resource. So this RFC treats fd as a container of address spaces which is each tagged by an IOASID. Thanks Kevin
