From owner-freebsd-hackers  Tue Jun 25 10:45:42 1996
Return-Path: owner-hackers
Received: (from root@localhost)
          by freefall.freebsd.org (8.7.5/8.7.3) id KAA21939
          for hackers-outgoing; Tue, 25 Jun 1996 10:45:42 -0700 (PDT)
Received: from june.cs.washington.edu (june.cs.washington.edu [128.95.1.4])
          by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id KAA21933
          for <freebsd-hackers@freebsd.org>; Tue, 25 Jun 1996 10:45:40 -0700 (PDT)
Received: (fgray@localhost) by june.cs.washington.edu (8.7.5/7.2ju) id KAA12278 for freebsd-hackers@freebsd.org; Tue, 25 Jun 1996 10:45:34 -0700
From: fgray@cs.washington.edu (Frederick Gray)
Message-Id: <199606251745.KAA12278@june.cs.washington.edu>
Subject: M_LEADINGSPACE
To: freebsd-hackers@freebsd.org
Date: Tue, 25 Jun 1996 10:45:34 -0700 (PDT)
X-Mailer: ELM [version 2.4 PL23]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: owner-hackers@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

In the following macro from sys/mbuf.h:

/*
 * Compute the amount of space available
 * before the current start of data in an mbuf.
 */
#define M_LEADINGSPACE(m) \
        ((m)->m_flags & M_EXT ? /* (m)->m_data - (m)->m_ext.ext_buf */ 0 : \
            (m)->m_flags & M_PKTHDR ? (m)->m_data - (m)->m_pktdat : \
            (m)->m_data - (m)->m_dat)

Would someone explain to me why the definition in the case where M_EXT is true 
was commented out and replaced with 0?  The original definition looks correct
to me.

-- Fred Gray
-- fgray@cs.washington.edu