[caf]

I had neither written code to test it nor was speculating - I was reading the kernel source, which is pretty clear (if you know in general how file polling is implemented in the Linux kernel).

However, because of what you have observed I wrote up a quick test, which confirms to my satisfaction that epoll_wait() respects SO_RCVLOWAT on TCP sockets: https://gist.github.com/keaston/d2473b8b996a34a5860b0744684f...

It seems likely that you must have been dealing with an old "enterprise" kernel in 2015 that hadn't had this fix backported to it?

[benwills]

Wow. When I saw your code, I thought to myself "yeah, but does it work when the socket is for a client?" Turns out, it does.

My only guess is that I was botching something else when I was digging into this a few years ago.

I can't tell you how much I appreciate you putting that together. This seriously changes a lot of what I work on. Thank you.

The client code I wrote: https://gist.github.com/benwills/95ee844853d3b18588fb3df7d56...

[caf]

Good example.

The errors are just because you need to check for EAGAIN or EWOULDBLOCK when read() returns -1, and not bail out when that happens.