On 11/7/23 4:55 PM, Mina Almasry wrote: > On Mon, Nov 6, 2023 at 4:03 PM Willem de Bruijn > <willemdebruijn.kernel@xxxxxxxxx> wrote: >> >> On Mon, Nov 6, 2023 at 3:55 PM David Ahern <dsahern@xxxxxxxxxx> wrote: >>> >>> On 11/6/23 4:32 PM, Stanislav Fomichev wrote: >>>>> The concise notification API returns tokens as a range for >>>>> compression, encoding as two 32-bit unsigned integers start + length. >>>>> It allows for even further batching by returning multiple such ranges >>>>> in a single call. >>>> >>>> Tangential: should tokens be u64? Otherwise we can't have more than >>>> 4gb unacknowledged. Or that's a reasonable constraint? >>>> >>> >>> Was thinking the same and with bits reserved for a dmabuf id to allow >>> multiple dmabufs in a single rx queue (future extension, but build the >>> capability in now). e.g., something like a 37b offset (128GB dmabuf >>> size), 19b length (large GRO), 8b dmabuf id (lots of dmabufs to a queue). >> >> Agreed. Converting to 64b now sounds like a good forward looking revision. > > The concept of IDing a dma-buf came up in a couple of different > contexts. First, in the context of us giving the dma-buf ID to the > user on recvmsg() to tell the user the data is in this specific > dma-buf. The second context is here, to bind dma-bufs with multiple > user-visible IDs to an rx queue. > > My issue here is that I don't see anything in the struct dma_buf that > can practically serve as an ID: > > https://elixir.bootlin.com/linux/v6.6-rc7/source/include/linux/dma-buf.h#L302 > > Actually, from the userspace, only the name of the dma-buf seems > queryable. That's only unique if the user sets it as such. The dmabuf > FD can't serve as an ID. For our use case we need to support 1 process > doing the dma-buf bind via netlink, sharing the dma-buf FD to another > process, and that process receives the data. In this case the FDs > shown by the 2 processes may be different. Converting to 64b is a > trivial change I can make now, but I'm not sure how to ID these > dma-bufs. Suggestions welcome. I'm not sure the dma-buf guys will > allow adding a new ID + APIs to query said dma-buf ID. > The API can be unique to this usage: e.g., add a dmabuf id to the netlink API. Userspace manages the ids (tells the kernel what value to use with an instance), the kernel validates no 2 dmabufs have the same id and then returns the value here.
