Date: Wed, 20 Nov 2013 20:21:47 +0000 From: "Robert N. M. Watson" <rwatson@FreeBSD.org> To: Julian Elischer <julian@FreeBSD.ORG> Cc: svn-src-head@freebsd.org, George Neville-Neil <gnn@FreeBSD.org>, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r258328 - head/sys/net Message-ID: <E91CDE96-52EF-45A2-9CAA-A6D3285F1D05@FreeBSD.org> In-Reply-To: <528D1768.9000401@freebsd.org> References: <201311182258.rAIMwEFd048783@svn.freebsd.org> <alpine.BSF.2.00.1311191101060.50802@fledge.watson.org> <528D1768.9000401@freebsd.org>
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On 20 Nov 2013, at 20:11, Julian Elischer <julian@FreeBSD.ORG> wrote:
>> Currently, it is quite easy to make mistakes regarding individual =
mbuf chains vs. lists of mbuf chains. This leads me to wonder whether a =
new type, perhaps simply constructed on the stack before passing in, =
should be used for KPIs that accept lists of packets. E.g.,
>>=20
>> /*
>> * This structure is almost always allocated on a caller stack, so
>> * cannot itself be queued without memory allocation in most =
cases.
>> */
>> struct mbuf_queue {
>> struct mbuf *mq_head;
>> };
>>=20
>>=20
> It's hard to believe that we don't have a structure around already =
that we can't use. With Luigi's comment, I wonder that there isn't an =
mbuf_list structure already we can just steal. it could almost be the =
current interface input queue structure.
The exact details don't matter; what does matter is that we make it as =
easy as possible to detect mistakes using the compiler (e.g., queue =
passed where mbuf expected, or vice versa) and that those situations we =
can't check statically, we try to check dynamically (multi-entry queue =
passed where mbuf expected). In the past we've had bugs along similar =
lines, where code expects m->m_nextpkt to be NULL when it isn't leading =
to very unhappy times in socket buffers, etc. Ideally what we did would =
have no expense at runtime unless debugging features were turned on =
(INVARIANTS).
Robert=
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