> From: Jason Gunthorpe <jgg@xxxxxxxxxx> > Sent: Wednesday, March 22, 2023 8:18 PM > > On Wed, Mar 22, 2023 at 08:17:54AM +0000, Liu, Yi L wrote: > > > Could you elaborate what is required with _INFO before libvirt can > > use a FD pass? > > Make a new _INFO that returns an array of dev_ids within the cdev's > iommufd_ctx that are part of the reset group, eg the devset. > > qemu will call this for each dev_id after it opens the cdev to > generate the groupings. Thanks. So this new _INFO only reports a limited scope instead of the full list of affected devices. Also, it is not static scope since device may be opened just after the _INFO returns. > > > But for the current qemu setup it will open cdev directly and it will > > > know the BDF so it can still use the current _INFO. > > > > > > Though it would be nice if qemu didn't need two implementations so Yi > > > I'd rather see a new info in this series as well and qemu can just > > > consistently use dev_id and never bdf in iommufd mode. > > > > I have one concern here. iommufd dev_id is not a static info as much as > > bdf. It is generated when bound to iommufd. So if there are devices that > > are affected but not bound to iommufd yet at the time of invoking _INFO, > > then the _INFO ioctl just gets a subset of the affected devices. Is it enough? > > I'd probably use similar logic as the reset path, if one of reset > group devices is open and on a different iommufd_ctx then fail the > IOCTL with EPERM. Say there are three devices in the dev_set. When the first device is opened by the current qemu, this new _INFO would return one dev_id to user. When the second device is opened, this new _INFO will return two dev_ids to user. If the third device is opened by another qemu, then the new _INFO would fail since the former two devices were opened and have different iommufd_ctx with the third device. Regards, Yi Liu
