Thanks for writing the man page too. I've made a few comments, mostly to make the English more grammatical and idiomatic.

This looks great, @kib! If you commit it, I'll follow up with the test suite. A few questions:

Wow! This looks much simpler than the original userspace-based implementation. I like it. I wrote some tests, too. I can commit those separately if you like, after you commit the main code. The only thing that's missing is a mention of the new option in mount_fusefs.8 . Could you please add that?

I'm afraid that with this latest patch, I get an instapanic on boot in pid 1.

Sorry, you're right @jlduran , as js just informed me elsewhere. My source tree was out of date. Sorry for the noise.

I had to build an aarch64 VM just to test the RFSPAWN change, but it works now. It probably works on amd64 too, but I can't test it without writing assembly code.

Add test cases

The new syscalls mostly work nicely. I've just found a few bugs. In addition to my inline comments, pdwait never returns a pid. It always returns 0. Is that deliberate? Also, it's unclear to me when a child ought to be reaped. I would think that it should be reaped as soon as pdwait or waitpid returns it (though the pid shouldn't be recycled until the process descriptor is closed). However, I'm seeing that the child doesn't get reaped until close(). That is, pdwait() will return the process multiple times, as if WNOWAIT were set. Is that deliberate?

Rather than add a new syscall for pdwait, what would you say to adding another idtype for waitid and wait6? We already have those syscalls, and their existing interface nicely allows for different kinds of ids. We would just need to add a P_PIDFD idtype value. That's also what Linux does.

• Style, suggested by des@
• Fix the encoded width of tcp-state, suggested by @des

LGTM. But you should wrap the long line in your commit message . And add something to the commit message indicating that the problem is with the "show" subcommand.