On Mon, 5 Oct 2020 12:16:10 -0400 Matthew Rosato <mjrosato@xxxxxxxxxxxxx> wrote: > On 10/5/20 12:01 PM, Cornelia Huck wrote: > > On Mon, 5 Oct 2020 09:52:25 -0400 > > Matthew Rosato <mjrosato@xxxxxxxxxxxxx> wrote: > > > >> On 10/2/20 5:44 PM, Alex Williamson wrote: > > > >>> Can you discuss why a region with embedded capability chain is a better > >>> solution than extending the VFIO_DEVICE_GET_INFO ioctl to support a > >>> capability chain and providing this info there? This all appears to be > >>> read-only info, so what's the benefit of duplicating yet another > >> > >> It is indeed read-only info, and the device region was defined as such. > >> > >> I would not necessarily be opposed to extending VFIO_DEVICE_GET_INFO > >> with these defined as capabilities; I'd say a primary motivating factor > >> to putting these in their own region was to avoid stuffing a bunch of > >> s390-specific capabilities into a general-purpose ioctl response. > > > > Can't you make the zdev code register the capabilities? That would put > > them nicely into their own configurable part. > > > > I can still keep the code that adds these capabilities in the zdev .c > file, thus meaning they will only be added for s390 zpci devices -- but > the actual definition of them should probably instead be in vfio.h, no? > (maybe that's what you mean, but let's lay it out just in case) > > The capability IDs would be shared with any other potential user of > VFIO_DEVICE_GET_INFO (I guess there is precedent for this already, > nvlink2 does this for vfio_region_info, see > VFIO_REGION_INFO_CAP_NVLINK2_SSATGT as an example). > > Today, ZPCI would be the only users of VFIO_DEVICE_GET_INFO capability > chains. Tomorrow, some other type might use them too. Unless we want > to put a stake in the ground that says there will never be a case for a > capability that all devices share on VFIO_DEVICE_GET_INFO, I think we > should keep the IDs unique and define the capabilities in vfio.h but do > the corresponding add_capability() calls from a zdev-specific file. Agreed. We should have enough space for multiple users, and I do not consider reserving the IDs cluttering.
