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From: Archie Cobbs <archie@whistle.com>
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Subject: Re: Proposal for ethernet, bridging, netgraph
In-Reply-To: <200004260211.WAA61401@whizzo.transsys.com> from "Louis A. Mamakos" at "Apr 25, 2000 10:11:28 pm"
To: louie@TransSys.COM (Louis A. Mamakos)
Date: Tue, 25 Apr 2000 19:29:49 -0700 (PDT)
Cc: archie@whistle.com (Archie Cobbs), luigi@FreeBSD.ORG,
	remy@boostworks.com, csg@waterspout.com, pavel@alum.mit.edu,
	nsayer@sftw.com, julian@elischer.org, freebsd-net@FreeBSD.ORG
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Louis A. Mamakos writes:
> Just a thought while looking at this code - in if_ethersubr.c where
> the bpf process has been moved, the same idiom is repeated that
> was in the drivers:
> 
>                /* Check for a BPF tap */
>                if (ifp->if_bpf != NULL) {
>                        struct mbuf m0;
> 
>                        /* OK because BPF treats the mbuf as read-only */
>                        m0.m_next = m;
>                        m0.m_data = (char *)eh;
>                        m0.m_len = ETHER_HDR_LEN;
>                        bpf_mtap(ifp, &m0);
>                }
> 
> Now that mbufs are 256 bytes long, is this getting to be too much data
> to stick on the kernel stack?  It seems like it's not a problem now, but
> this code is now going to be invoked deeper in the stack than before.
> 
> If this code is running at splnet(), then it ought to be safe to just
> have a static mbuf laying about for this purpose, rather than allocating
> a local on the kernel stack.

Good point.. we could just use a struct m_hdr.. and in any case
it should be able to be a static variable.. we're at splnet().

-Archie

___________________________________________________________________________
Archie Cobbs   *   Whistle Communications, Inc.  *   http://www.whistle.com


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