Date: Thu, 11 Sep 2008 12:04:49 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: vehemens <vehemens@verizon.net> Cc: freebsd-current@freebsd.org, Robert Watson <rwatson@freebsd.org> Subject: Re: cdefpriv usage (was: bsd versus linux device drivers) Message-ID: <20080911090449.GV39652@deviant.kiev.zoral.com.ua> In-Reply-To: <200809102307.31209.vehemens@verizon.net> References: <200809080202.00664.vehemens@verizon.net> <alpine.BSF.1.10.0809081434200.37494@fledge.watson.org> <200809080950.55528.vehemens@verizon.net> <200809102307.31209.vehemens@verizon.net>
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On Wed, Sep 10, 2008 at 11:07:31PM -0700, vehemens wrote:
> On Monday 08 September 2008 09:50:55 am vehemens wrote:
> > On Monday 08 September 2008 06:41:53 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 a=
nd a
> > > >>> calling argument structure called struct file. It provides a pri=
vate
> > > >>> 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 lo=
oks
> > > > 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=3Dbigexcerpts;i=3Ddevfs_set_cde=
vpriv
> > >
> > > 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 bpfioc=
tl()
> > > might be called without its cdev-private data?
> >
> > Got it now. Looks like the converted drivers are only in current, but =
the
> > KPI is in at least 7.x as well.
>=20
> My first impression based on the modified drivers, was that I only needed=
to=20
> add a get to open, and set's to ioctl, mmap, read, write, close etc. Als=
o=20
> that the data release would occur after the close call via the function=
=20
> provided to get.
I do not know whether this is an slip of keyboard, but most typically,
you need set in open, and get in the read/write/mmap.
> Don't have a problem with set, but some or all of the get's fail. I see=
=20
> lot's of error=3D2 in ioctl, and error=3D9 in mmap, Going to instrument =
the code=20
> next. Any suggestions would be helpful.
>=20
> On a side note, I had to first upgrade my 7.x system and was wondering if=
=20
> there was a FreeBSD_version number for this feature?
I do not remember, and in fact I do not see a reason for bumping version
for this feature. In-tree drivers do not need the check, since they are
in _the_ tree. Moreover, the cdevpriv does not change existing KPI, it
only adds a bunch of functions. Increasing version for each KPI addition
is rather pointless, IMHO.
Also, see man(9) update at
http://people.freebsd.org/~kib/misc/man9.1.patch
that, among other items, contains start of the cdevpriv documentation.
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