Date: Mon, 8 Sep 2008 14:41:53 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: vehemens <vehemens@verizon.net> Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-current@freebsd.org Subject: Re: bsd versus linux device drivers Message-ID: <alpine.BSF.1.10.0809081434200.37494@fledge.watson.org> In-Reply-To: <200809080350.41579.vehemens@verizon.net> References: <200809080202.00664.vehemens@verizon.net> <20080908100415.GI2038@deviant.kiev.zoral.com.ua> <200809080350.41579.vehemens@verizon.net>
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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
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