[Libguestfs] [PATCH nbdkit 0/3] server: Implement TCP fastopen (TFO)

TCP fastopen is a little-known feature for omitting part of the normal 3-way handshake. It's implemented in Linux (since ~2014), Windows (since 2016), macOS and FreeBSD, but this implementation probably only works on Linux. The heavy lifting is done by the kernel, and the userspace changes needed (on Linux, at least) are very minor. I'm mainly posting this to save the patch series. After going down a rabbit hole testing and benchmarking this, it seems to make no discernable difference that I can see, or any benefit must be under the margin of error from measurement. It's probably safe to include this feature, but on the other hand if it doesn't do anything it seems to just add unnecessary complexity. There is a corresponding libnbd series which also contains the benchmark program, which I'll post in a moment. Rich.