Re: Probs with PCI bus master DMA to user space

[Jeff Garzik]

On Tue, 20 Feb 2001, Norbert Roos wrote:

> Jeff Garzik wrote:
> 
> > > But the buffers are usually allocated with malloc() by any application
> > > which wants to use my driver.. otherwise my driver would have to offer a
> > > malloc-like function, but I can hardly force the application to use my
> > > own malloc function.
> > 
> > If you are writing the driver, sure you can.
> 
> ??
> 
> The application is doing something like
> 
>   fd = open("/dev/mydriver");
>   buf = malloc();
>   fill_buffer_with_data(buf);
>  write(fd,buf);
> 
> And now i should tell the programmer not to use malloc() but my special
> driver-malloc?
> Or do you mean something different?

fd = open(...);
buf = mmap(fd, ...);
fill_buffer_with_data(buf);
ioctl(fd, ...); /* tell kernel data is there */

There are variations depending on the application, but you get the
picture.  A buffer copy is eliminated when mmap is used, too, making
your application faster.

	Jeff