On Thu, Feb 13, 2020 at 10:59:34AM -0500, Michael S. Tsirkin wrote: > On Thu, Feb 13, 2020 at 11:51:54AM -0400, Jason Gunthorpe wrote: > > The 'class' is supposed to provide all the library functions to remove > > this duplication. Instead of plugging the HW driver in via some bus > > scheme every subsystem has its own 'ops' that the HW driver provides > > to the subsystem's class via subsystem_register() > > Hmm I'm not familiar with subsystem_register. A grep didn't find it > in the kernel either ... I mean it is the registration function provided by the subsystem that owns the class, for instance tpm_chip_register(), ib_register_device(), register_netdev(), rtc_register_device() etc So if you have some vhost (vhost net?) class then you'd have some vhost_vdpa_init/alloc(); vhost_vdpa_register(), sequence presumably. (vs trying to do it with a bus matcher) I recommend to look at rtc and tpm for fairly simple easy to follow patterns for creating a subsystem in the kernel. A subsystem owns a class, allows HW drivers to plug in to it, and provides a consistent user API via a cdev/sysfs/etc. The driver model class should revolve around the char dev and sysfs uABI - if you enumerate the devices on the class then they should all follow the char dev and sysfs interfaces contract of that class. Those examples show how to do all the refcounting semi-sanely, introduce sysfs, cdevs, etc. I thought the latest proposal was to use the existing vhost class and largely the existing vhost API, so it probably just needs to make sure the common class-wide stuff is split from the 'driver' stuff of the existing vhost to netdev. Jason
