Re: What is the intended function of open() system call?
Arvind Sankar (arvinds@mit.edu)
Fri, 2 Apr 1999 09:43:48 -0500
On Fri, Apr 02, 1999 at 09:07:59AM -0500, Richard B. Johnson wrote:
> On Thu, 1 Apr 1999, Vassili Leonov wrote:
>
> > I was coding a driver and come to a realisation that open() system call is
> > not a good place to prepare hardware for read or write operatioin, since
> > dd for example uses RDWR mode to open of= device. And there is no warranty
> > othewise. Generally, seems like this is a bug in Unix design, but maybe I
> > do not understand something. Or maybe it's a long lining bug in dd...
> >
> In your cited example of O_RDWR, you probably want to allow the device
> to be opened R/W (with attributes), but if the illegal operation within
> the driver occurs, you return a failure code, probably -ENOSYS.
>
I think Leonov meant that the driver won't know inside open() whether it's
going to be read or written (since dd opens O_RDWR when it wants O_WRONLY), so
if different initialization is required for the two, you're screwed.
-- arvind
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