On Mon, Nov 6, 2023 at 4:03 PM Willem de Bruijn willemdebruijn.kernel@gmail.com wrote:
On Mon, Nov 6, 2023 at 3:55 PM David Ahern dsahern@kernel.org 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#L30...
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.
-- Thanks, Mina