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Date: Mon, 4 Jan 2016 10:54:15 +0200
From: Konstantin Belousov <kostikbel@gmail.com>
To: Mark Delany <c2h@romeo.emu.st>
Cc: freebsd-net@freebsd.org
Subject: Re: Does FreeBSD have sendmmsg or recvmmsg system calls?
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On Sun, Jan 03, 2016 at 09:47:20PM +0000, Mark Delany wrote:
> Eg, if a signal arrives after
> more than zero packets have been processed by recvmmsg() what is the
> correct return value? -1 or the count of messages returned?

This is really not a question to consider different answers. Unix
already made a (right, IMO) decision there, e.g. for read(2) syscall.
If any data was actually read, the length of the consumed data must be
returned, and not the error.

Typically, socket functions return error on the next call, if the
current call must still return data.  This is why so_error is there.