On Wed, Dec 2, 2020 at 7:13 PM Parav Pandit <pa...@nvidia.com> wrote: > > > > > From: Yongji Xie <xieyon...@bytedance.com> > > Sent: Wednesday, December 2, 2020 2:52 PM > > > > On Wed, Dec 2, 2020 at 12:53 PM Parav Pandit <pa...@nvidia.com> wrote: > > > > > > > > > > > > > From: Yongji Xie <xieyon...@bytedance.com> > > > > Sent: Wednesday, December 2, 2020 9:00 AM > > > > > > > > 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? > > > > > > > For block device there is certainly some backend to process the IOs. > > > Sometimes backend to be setup first, before its front end is exposed. > > > > Yes, the backend need to be setup firstly, this is vendor device specific, > > not > > vdpa specific. > > > > > "vdpa dev add" is the front end command who connects to the backend > > (implicitly) for network device. > > > > > > vhost->vdpa_block_device->backend_io_processor (usr,hw,kernel). > > > > > > And it needs a way to connect to backend when explicitly specified during > > creation time. > > > Something like, > > > $ vdpa dev add parentdev vdpa_vduse type block name foo3 handle > > <uuid> > > > In above example some vendor device specific unique handle is passed > > based on backend setup in hardware/user space. > > > > > > > Yes, we can work like this. After we setup a backend through an anonymous > > inode(fd) from /dev/vduse, we can get a unique handle. Then use it to > > create a frontend which will connect to the specific backend. > > I do not fully understand the inode. But I assume this is some unique handle > say uuid or something that both sides backend and vdpa device understand. > It cannot be some kernel internal handle expose to user space. >
Yes, the unique handle should be a user-defined stuff. > > > > > In below 3 examples, vdpa block simulator is connecting to backend block > > or file. > > > > > > $ vdpa dev add parentdev vdpa_blocksim type block name foo4 blockdev > > > /dev/zero > > > > > > $ vdpa dev add parentdev vdpa_blocksim type block name foo5 blockdev > > > /dev/sda2 size=100M offset=10M > > > > > > $ vdpa dev add parentdev vdpa_block filebackend_sim type block name > > > foo6 file /root/file_backend.txt > > > > > > Or may be backend connects to the created vdpa device is bound to the > > driver. > > > Can vduse attach to the created vdpa block device through the char device > > and establish the channel to receive IOs, and to setup the block config > > space? > > > > > > > How to create the vdpa block device? If we use the command "vdpa dev > > add..", the command will hang there until a vduse process attaches to the > > vdpa block device. > I was suggesting that vdpa device is created, but it doesn’t have backend > attached to it. > It is attached to the backend when ioctl() side does enough setup. This state > is handled internally the vduse driver. > > But the above method of preparing backend looks more sane. > > Regardless of which method is preferred, vduse driver must need a state to > detach the vdpa bus device queues etc from the user space. > This is needed because user space process can terminate anytime resulting in > detaching dpa bus device in_use by the vhost side. I think the vdpa device should only be detached by the command "vdpa dev del...". The vduse driver can support reconnecting when user space process is terminated. Thanks, Yongji