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Date: Mon, 27 Apr 2015 08:50:20 +0300
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: John-Mark Gurney <jmg@funkthat.com>
Cc: freebsd-net@FreeBSD.org, Poul-Henning Kamp <phk@phk.freebsd.dk>
Subject: Re: should m_copyback possibly throw data away?
Message-ID: <20150427055020.GC883@FreeBSD.org>
References: <20150424181158.GJ37063@funkthat.com>
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On Fri, Apr 24, 2015 at 11:23:08AM -0700, John-Mark Gurney wrote:
J> John-Mark Gurney wrote this message on Fri, Apr 24, 2015 at 11:11 -0700:
J> > I would also be fine w/ documenting this behavior, though I'm sure
J> > it'd be surprising to many that you'd have to check to make sure your
J> > data was properly copied.
J> 
J> Should have reviewed the m_copyback function before sending this
J> email...
J> 
J> It gets worse..  If the m_get to extend it fails, there is no
J> notification that your data didn't get copyied into the mbuf.. and no
J> warning in the man page that this function is unsafe and may cause
J> data loss...
J> 
J> Comments?

My suggestion is:

1) make it return int
2) change first check to KASSERT
3) add wait parameter
4) while here change relic of c_caddr_t to const char *

Yes, this requires some time.

You can also look at OpenBSD/NetBSD.

-- 
Totus tuus, Glebius.