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Hello,

> Okay, I have a concern this.  As far as I can tell, the cookie is
> passed to the driver, but I cannot see how the driver can make sense
> of it.  The cookie that wsdisplay passes seems to be a struct
> wsscreen, which is a private structure to wsdisplay(4) -- it is not
> declared in any external headers.

struct wsscreen is not really defined anywhere I can see. What you get
in ioctl() and mmap() is supposedly the screen struct your
alloc_screen() method produced ( or vcons_alloc_screen(), in this case
it's a struct vcons_screen * ). Since its content is driver specific
it's handled as opaque cookie in wsdisplay.c

> So how is a display driver (e.g. machfb, or more to the point, my
> radeonfb driver) supposed to use this member argument?=20

Cast it to your driver-specific struct screen.

> Pass an opaque cookie is useless to the driver unless there is some
> way for the driver to do something meaningful with it.

The driver defines this cookie, it's opaque to anyone /but/ the driver.

have fun
Michael

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