For example, splice or tcp_mmap() can be used to "receive" data from networking stack into application managed place. splice and MSG_ZEROCOPY can be used to "tr

For example, splice or tcp_mmap() can be used to "receive" data from networking stack into application managed place. splice and MSG_ZEROCOPY can be used to "transmit" data into networking stack. The problem with MSG_ZEROCOPY is that, while buffers belong to application, the API doesn't tell you when it's done sending and it's possible to repurpose the buffers. This io_uring article seem to indicate this fault has been fixed in io_uring zerocopy API. This is the hard part of a zero-copy API, and why its hard to make a zero-copy API that's a drop-in replacement for sockets and can magically enable naive applications to have zero-copy transmits. I attempted to do zero-copy sockets in FreeBSD ~20+ years ago (https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.34.8745&rep=rep1&type=pdf https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.34...). What's not mentioned in the paper is that the change was an overall net-negative, because applications would frequently trigger a COW fault when attempting to write to a buffer owned by the kernel.