From owner-freebsd-questions@FreeBSD.ORG  Sat Feb 17 09:29:17 2007
Return-Path: <owner-freebsd-questions@FreeBSD.ORG>
X-Original-To: freebsd-questions@FreeBSD.org
Delivered-To: freebsd-questions@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52])
	by hub.freebsd.org (Postfix) with ESMTP id B9C4416A408;
	Sat, 17 Feb 2007 09:29:17 +0000 (UTC) (envelope-from aji@katuns.org)
Received: from host06.mywebns.com (host06.mywebns.com [69.65.107.207])
	by mx1.freebsd.org (Postfix) with ESMTP id 8F2FE13C442;
	Sat, 17 Feb 2007 09:29:17 +0000 (UTC) (envelope-from aji@katuns.org)
Received: from katunsor by host06.mywebns.com with local (Exim 4.63)
	(envelope-from <aji@katuns.org>)
	id 1HIKyX-0003aL-Bw; Sat, 17 Feb 2007 08:31:21 +0000
Received: from 122.167.57.52 ([122.167.57.52])
	(SquirrelMail authenticated user aji@katuns.org)
	by katuns.org with HTTP; Sat, 17 Feb 2007 08:31:21 -0000 (GMT)
Message-ID: <41759.122.167.57.52.1171701081.squirrel@katuns.org>
Date: Sat, 17 Feb 2007 08:31:21 -0000 (GMT)
From: aji@katuns.org
To: freebsd-questions@FreeBSD.org
User-Agent: SquirrelMail/1.4.9a
MIME-Version: 1.0
Content-Type: text/plain;charset=iso-8859-1
Content-Transfer-Encoding: 8bit
X-Priority: 3 (Normal)
Importance: Normal
Sender: <katunsor@host06.mywebns.com>
X-AntiAbuse: This header was added to track abuse,
	please include it with any abuse report
X-AntiAbuse: Primary Hostname - host06.mywebns.com
X-AntiAbuse: Original Domain - freebsd.org
X-AntiAbuse: Originator/Caller UID/GID - [32051 500] / [47 12]
X-AntiAbuse: Sender Address Domain - katuns.org
X-Source: 
X-Source-Args: 
X-Source-Dir: 
X-Mailman-Approved-At: Sat, 17 Feb 2007 16:24:13 +0000
Cc: freebsd-doc@FreeBSD.org
Subject: softc And device_get_softc(dev)
X-BeenThere: freebsd-questions@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: User questions <freebsd-questions.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>, 
	<mailto:freebsd-questions-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-questions>
List-Post: <mailto:freebsd-questions@freebsd.org>
List-Help: <mailto:freebsd-questions-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-questions>, 
	<mailto:freebsd-questions-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Sat, 17 Feb 2007 09:29:17 -0000

hi

   My name is Aji Abraham, now working with device drivers. the word
"softc" and the function "device_get_softc(dev)" getting confuse me a
lot. am listing some query below ..  pls help me ..


Q1 In a free BSD driver Code, there are two device depended structures

     struct xx_softc {
     .......
     ......


     };

     struct xx_if_softc {
     .......
     ......


     };

sizeof(struct xx_softc ) is 68
sizeof(struct xx_if_softc ) is 1186

And in device attach function

     xx_attach(dev){

     struct xx_softc    *sc;
     struct xx_if_softc *if_sc;

     sc_if = device_get_softc(dev);
     sc = device_get_softc(device_get_parent(dev));

     sc_if-> .....
     sc-> ....
     .......
     ......

     }


Both allocation uses the same function. How it possible ?  can we access
all structure member ?

Regards

Aji Abraham