KQueue 0-length UDP packet

Fedor Indutny fedor at indutny.com
Sat Aug 2 10:41:48 UTC 2014

Guess I know the answer:


Basically, OSX is checking `kn_data` and FreeBSD is using

Thank you anyway!

On Sat, Aug 2, 2014 at 1:39 PM, Fedor Indutny <fedor at indutny.com> wrote:

> Hello!
> I'm trying to figure out, why this code:
> https://github.com/indutny/0-udp
> Which basically sends a 0-length UDP packet to a server and polls
> kqueue events on the server fd.
> Return 1 kevent on FreeBSD, and blocks indefinitely without
> returning any events on OSX.
> So far I could see that FreeBSD and OSX are treating NOTE_LOWAT
> differently:
> *
> https://github.com/opensource-apple/xnu/blob/2fa84067f6cdeb23267f877ca4fd26201316da1b/bsd/kern/uipc_socket.c#L4461
> *
> https://github.com/freebsd/freebsd/blob/6901832d8588537c81afbdb91d1a22deb5582c47/sys/kern/uipc_socket.c#L3163-L3164
> FreeBSD's NOTE_LOWAT is overriding SO_RCVLOWAT, and OSX is using
> SO_RVCLOWAT as a minimum value. But, since NOTE_LOWAT is not
> involved here by default, I'm failing to see where exactly this
> event could pass through kqueue filter.
> Could anyone with UDP and/or KQueue implementation knowledge
> share some insights with me?
> Thank you very much!
> Fedor.
> (NOTE: Duplicate, first email wasn't posted, because I wasn't subscribed
> to the ML)

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