Doudts in "softc" and "device_get_softc(dev)"

[John Baldwin]

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