Maybe add a comma here after "included".

Is this going to be a problem when upgrading with an old sysctl.conf?

The description of gzio_init should move up because: it's the first function and you just wrote "Finally" in line 67.

I think we're depreciating u_int & friends.

Can we abstract the call to vn_rdwr_inchunks with a static function? I never really liked the fact that we call vn_rdwr_inchunks so many times when the only thing that changes is the the address space parameter.

Idem.

It would be safer if you bzero it. I think "gzs" might be uninitialised.

Can 'room' be zero?

Ok.

-1 is just the default zlib value, which happens to be 6. I just thought it would be clearer to do that. So this change has no actual effect.

Ok. I tried to write it so that the first paragraph was a summary of all the functions, and then subsequent paragraphs described the arguments of gzio_init() and friends. It's kind of confusing though, I'll rework it.

I think that only applies to u_intXX_t. There's no uint_t in FreeBSD to replace u_int either.

Good point. I'll rename core_gz_output_cb to core_write() without changing the body, and convert all the callers of vn_rdwr*.

Ok.

Yes. That case (room < 2) is handled by the if statement right at the end of the loop. It's a bit ugly, but I want to minimize invocations of the callback, so I try to pack the trailer into the output buffer whenever possible (which is most of the time) instead of always invoking the callback once for the trailer.

I meant unsigned int. :-)

This now uses UIO_SYSSPACE instead of UIO_USERSPACE. Is that ok?

Got it.

Ok, I'll change it to unsigned int.

Nope. Thanks for catching that - I forgot to test the last revision with compression disabled.