bsd versus linux device drivers

[Robert Watson]

On Mon, 8 Sep 2008, vehemens wrote:

> On Monday 08 September 2008 03:04:15 am Kostik Belousov wrote:
>> On Mon, Sep 08, 2008 at 02:02:00AM -0700, vehemens wrote:
>>> In linux drivers, there is a one to one relationship to an open and a 
>>> calling argument structure called struct file.  It provides a private data 
>>> pointer that allows the driver to preserve unique state information across 
>>> other calls such as read/write/ioctl/mmap/close etc.
>>>
>>> For bsd drivers, my understanding there is not an equivalent.  As a result 
>>> it is not possible to preserve different state information for multiple 
>>> opens by the same thread of the same device major/minor #'s.
>>>
>>> Is this correct, or did i miss something?
>>
>> There is devfs_{get,set}_cdevpriv() KPI. Still no manpage, I shall fix this 
>> ASAP.
>
> Just started looking at the firewire driver which has clone.  It looks like 
> it hooks into the event handler.
>
> Don't quite understand it all yet, so I'm going to look forward to that man 
> page.

Many device drivers continue to use the old clone interface, but are gradually 
being converted over.  You can look at the definitions and list of converted 
drivers here:

   http://fxr.watson.org/fxr/ident?im=bigexcerpts;i=devfs_set_cdevpriv

Looking at some of the converted drivers, I find myself a bit worried by the 
extra error handling: in what situations do we expect that bpfioctl() might be 
called without its cdev-private data?

Robert N M Watson
Computer Laboratory
University of Cambridge