Date: Tue, 20 Feb 2007 11:31:18 -0500 From: John Baldwin <jhb@freebsd.org> To: freebsd-drivers@freebsd.org Cc: aji abraham <abraham_aji@yahoo.co.in> Subject: Re: Doudts in "softc" and "device_get_softc(dev)" Message-ID: <200702201131.18873.jhb@freebsd.org> In-Reply-To: <150997.27592.qm@web8315.mail.in.yahoo.com> References: <150997.27592.qm@web8315.mail.in.yahoo.com>
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On Saturday 17 February 2007 04:41, aji abraham wrote:
> 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 ..
A softc is the driver-private "instance" data for each device. The
driver tells the kernel how big of a softc it wants and as a
convenience the kernel will go ahead and allocate it and zero it for
the driver.
> 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 ?
It is the same function, but it is getting called with different device_t
arguments, so it will return different pointers.
> can we
> access
> all structure member ?
Yes.
--
John Baldwin
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