Subject: Re: File I/O in hardware device driver
To: Steven Grunza <>
From: Eduardo Horvath <>
List: tech-kern
Date: 07/28/2000 11:15:12
What ARE you doing?

On Fri, 28 Jul 2000, Steven Grunza wrote:

> Two possible problems with my driver just occurred to me:
> 1)  Doing file IO from a hardware device driver might not be a good
> idea.  Is it legal for an IOCTL to my driver to provide the name of a
> file which my driver then opens with your typical open() or fopen() type
> of call?

That is not a good thing to do.  A driver should not be opening
files.  That's for applications to do.

> 2)  Allocating 600+KB of physical memory (wired to prevent swapping it
> out) may be a bad idea.  How much is available?  Is it configurable?
> The application software requires 128MB in a system so there should be
> enough physical memory in the box but can a malloc() in the kernel grab
> a 600+KB chunk of contiguous, non-swappable memory?

600+KB of kernel memory is a rather large chunk.  Virtually contiguous or
physically contiguous?  Virtually contiguous is relatively
easy.  Physically contiguous is not.

> 2a) How should I allocate this memory?  Would it be a MALLOC(9) call or
> some kind of a uvm_pagealloc(9) call?  This code will need to run on any
> system with a PCI bus, i386 and SPARC for certain.  Possibly others....

You should use bus_dmamem_alloc(9).  See bus_dma(9).  You should also be
using the bus_space interfaces.  See bus_space(9).

Eduardo Horvath