bsd versus linux device drivers

John Baldwin jhb at freebsd.org
Mon Sep 8 21:31:07 UTC 2008


On Monday 08 September 2008 09:41:53 am Robert Watson wrote:
> 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?

I think that is just hyper-paranoia.

-- 
John Baldwin


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