From owner-p4-projects@FreeBSD.ORG  Thu May 17 09:27:56 2007
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From: Hans Petter Selasky <hselasky@freebsd.org>
To: Sepherosa Ziehau <sephe@freebsd.org>
Date: Thu, 17 May 2007 10:27:40 +0200
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Cc: Perforce Change Reviews <perforce@freebsd.org>
Subject: Re: PERFORCE change 119878 for review
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Hi,

1) Maybe you should bump __FreeBSD_version when this is introduced into HEAD.

2) Are you sure that you want to do this?

If you look at the implementation of "m_adj()" for a negative number it is not 
too efficient. With regard to "if_ural.c" it is faster to remove those bytes 
at an earlier point. And then just never set M_HASFCS at all.

--HPS

>
> ==== //depot/projects/wifi/sys/dev/usb/if_ural.c#25 (text+ko) ====
>
> @@ -939,7 +939,6 @@
>  	/* finalize mbuf */
>  	m->m_pkthdr.rcvif = ifp;
>  	m->m_pkthdr.len = m->m_len = (le32toh(desc->flags) >> 16) & 0xfff;
> -	m->m_flags |= M_HASFCS;	/* h/w leaves FCS */
>
>  	if (bpf_peers_present(sc->sc_drvbpf)) {
>  		struct ural_rx_radiotap_header *tap = &sc->sc_rxtap;
> @@ -954,6 +953,9 @@
>  		bpf_mtap2(sc->sc_drvbpf, tap, sc->sc_rxtap_len, m);
>  	}
>
> +	/* Strip trailing 802.11 MAC FCS. */
> +	m_adj(m, -IEEE80211_CRC_LEN);
> +
>  	wh = mtod(m, struct ieee80211_frame *);
>  	ni = ieee80211_find_rxnode(ic, (struct ieee80211_frame_min *)wh);
>
>

--HPS