On Tue, Dec 1, 2020 at 7:32 PM Parav Pandit <pa...@nvidia.com> wrote: > > > > > From: Yongji Xie <xieyon...@bytedance.com> > > Sent: Tuesday, December 1, 2020 3:26 PM > > > > On Tue, Dec 1, 2020 at 2:25 PM Jason Wang <jasow...@redhat.com> wrote: > > > > > > > > > On 2020/11/30 下午3:07, Yongji Xie wrote: > > > >>> Thanks for adding me, Jason! > > > >>> > > > >>> Now I'm working on a v2 patchset for VDUSE (vDPA Device in > > > >>> Userspace) [1]. This tool is very useful for the vduse device. So > > > >>> I'm considering integrating this into my v2 patchset. But there is > > > >>> one problem： > > > >>> > > > >>> In this tool, vdpa device config action and enable action are > > > >>> combined into one netlink msg: VDPA_CMD_DEV_NEW. But in vduse > > > >>> case, it needs to be splitted because a chardev should be created > > > >>> and opened by a userspace process before we enable the vdpa device > > > >>> (call vdpa_register_device()). > > > >>> > > > >>> So I'd like to know whether it's possible (or have some plans) to > > > >>> add two new netlink msgs something like: VDPA_CMD_DEV_ENABLE > > and > > > >>> VDPA_CMD_DEV_DISABLE to make the config path more flexible. > > > >>> > > > >> Actually, we've discussed such intermediate step in some early > > > >> discussion. It looks to me VDUSE could be one of the users of this. > > > >> > > > >> Or I wonder whether we can switch to use anonymous inode(fd) for > > > >> VDUSE then fetching it via an VDUSE_GET_DEVICE_FD ioctl? > > > >> > > > > Yes, we can. Actually the current implementation in VDUSE is like > > > > this. But seems like this is still a intermediate step. The fd > > > > should be binded to a name or something else which need to be > > > > configured before. > > > > > > > > > The name could be specified via the netlink. It looks to me the real > > > issue is that until the device is connected with a userspace, it can't > > > be used. So we also need to fail the enabling if it doesn't opened. > > > > > > > Yes, that's true. So you mean we can firstly try to fetch the fd binded to a > > name/vduse_id via an VDUSE_GET_DEVICE_FD, then use the > > name/vduse_id as a attribute to create vdpa device? It looks fine to me. > > I probably do not well understand. I tried reading patch [1] and few things > do not look correct as below. > Creating the vdpa device on the bus device and destroying the device from the > workqueue seems unnecessary and racy. > > It seems vduse driver needs > This is something should be done as part of the vdpa dev add command, instead > of connecting two sides separately and ensuring race free access to it. > > So VDUSE_DEV_START and VDUSE_DEV_STOP should possibly be avoided. >
Yes, we can avoid these two ioctls with the help of the management tool. > $ vdpa dev add parentdev vduse_mgmtdev type net name foo2 > > When above command is executed it creates necessary vdpa device foo2 on the > bus. > When user binds foo2 device with the vduse driver, in the probe(), it creates > respective char device to access it from user space. But vduse driver is not a vdpa bus driver. It works like vdpasim driver, but offloads the data plane and control plane to a user space process. Thanks, Yongji
