Hi folks, The issue of sharing buffers between guests and hosts keeps poping up again and again in different contexts. Most recently here: https://www.mail-archive.com/qemu-devel@xxxxxxxxxx/msg656685.html So, I'm grabbing the recipient list of the virtio-vdec thread and some more people I know might be interested in this, hoping to have everyone included. Reason is: Meanwhile I'm wondering whenever "just use virtio-gpu resources" is really a good answer for all the different use cases we have collected over time. Maybe it is better to have a dedicated buffer sharing virtio device? Here is the rough idea: (1) The virtio device ===================== Has a single virtio queue, so the guest can send commands to register and unregister buffers. Buffers are allocated in guest ram. Each buffer has a list of memory ranges for the data. Each buffer also has some properties to carry metadata, some fixed (id, size, application), but also allow free form (name = value, framebuffers would have width/height/stride/format for example). (2) The linux guest implementation ================================== I guess I'd try to make it a drm driver, so we can re-use drm infrastructure (shmem helpers for example). Buffers are dumb drm buffers. dma-buf import and export is supported (shmem helpers get us that for free). Some device-specific ioctls to get/set properties and to register/unregister the buffers on the host. (3) The qemu host implementation ================================ qemu (likewise other vmms) can use the udmabuf driver to create host-side dma-bufs for the buffers. The dma-bufs can be passed to anyone interested, inside and outside qemu. We'll need some protocol for communication between qemu and external users interested in those buffers, to receive dma-bufs (via unix file descriptor passing) and update notifications. Dispatching updates could be done based on the application property, which could be "virtio-vdec" or "wayland-proxy" for example. commments? cheers, Gerd
