On Tue, Dec 1, 2020 at 11:59 PM Parav Pandit <pa...@nvidia.com> wrote: > > > > > From: Yongji Xie <xieyon...@bytedance.com> > > Sent: Tuesday, December 1, 2020 7:49 PM > > > > 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. > > > I see. So vduse cannot work with any existing vdpa devices like ifc, mlx5 or > netdevsim. > It has its own implementation similar to fuse with its own backend of choice. > More below. > > > 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. > > In that case to draw parallel lines, > > 1. netdevsim: > (a) create resources in kernel sw > (b) datapath simulates in kernel > > 2. ifc + mlx5 vdpa dev: > (a) creates resource in hw > (b) data path is in hw > > 3. vduse: > (a) creates resources in userspace sw > (b) data path is in user space. > hence creates data path resources for user space. > So char device is created, removed as result of vdpa device creation. > > For example, > $ vdpa dev add parentdev vduse_mgmtdev type net name foo2 > > Above command will create char device for user space. > > Similar command for ifc/mlx5 would have created similar channel for rest of > the config commands in hw. > vduse channel = char device, eventfd etc. > ifc/mlx5 hw channel = bar, irq, command interface etc > Netdev sim channel = sw direct calls > > Does it make sense?
In my understanding, to make vdpa work, we need a backend (datapath resources) and a frontend (a vdpa device attached to a vdpa bus). In the above example, it looks like we use the command "vdpa dev add ..." to create a backend, so do we need another command to create a frontend? Thanks, Yongji
