Date:	Fri, 21 Jul 2006 17:30:37 -0300
From:	Mauro Carvalho Chehab <mchehab@...radead.org>
To:	Trent Piepho <xyzzy@...akeasy.org>
Cc:	v4l-dvb maintainer list <v4l-dvb-maintainer@...uxtv.org>,
	Linux and Kernel Video <video4linux-list@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [v4l-dvb-maintainer] Re: [PATCH] V4L: struct video_device
	corruption

Hi, Trent,

Em Sex, 2006-07-21 às 13:06 -0700, Trent Piepho escreveu:
> I've trimmed the CCs, they were getting big and it didn't look like anyone
> else is taking part.
Ok.
> 
> I have a fix for the immediate issue of struct video_device, it doesn't fix
> everything else, but does fix this bug.
> http://linuxtv.org/hg/~tap/v4l-dvb?cmd=changeset;node=f3cc7acae78a;style=gitweb
> 
> On Fri, 21 Jul 2006, Mauro Carvalho Chehab wrote:
> > Em Qui, 2006-07-20 s 14:57 -0700, Trent Piepho escreveu:
> > > I've looked into this more, and there is still a serious bug here.  If you
> > > turn off V4L1 and V4L1_COMPAT, many drivers will a big issue with struct
> > > video_device.
> > If you turn V4L and V4L1_COMPAT off, most drivers won't compile.
> 
> There are many drivers which depend on VIDEO_V4L1 in Kconfig.  But, there
> are many drivers that don't depend on it.  All those drivers will compile
> with V4L1 turned all the way off.  I was able to compile 101 modules
> without V4L1 turned on.
> 
> > > In some files (saa7134-tvaudio.c, saa6752hs.c, v4l2-common.c, dozens
> > > more), V4L1 will be off and HAVE_V4L1 will not be defined.  This gives you
> > > the struct video_dev _without_ vidiocgmbuf.
> > Ok.
> > >
> > > In other files (tveeprom.c, tvaudio.c, bttv-driver.c, and many more), V4L1
> > > will still be off (of course) by HAVE_V4L1 _will_ be defined.  This gives
> > > you the struct viddeo_dev _with_ vidiocgmbuf.
> > Hmm... tveeprom shouln't include videodev but, instead, videodev2.
> > Anyway, both aren't dependent of v4l2-dev.h. For bttv, it is not really
> > a complete V4L2 driver and should be disabled. You should also notice
> > that tvaudio is part of bttv stuff (although also not dependent of
> > video_device struct and v4l2-dev.h).
> 
> Well, tvaudio.c does include v4l2-dev.h.  There are more that do this:
> 
> bttv-cards.c   bttv-vbi.c        msp3400-kthreads.c  tuner-core.c
> bttv-driver.c  compat_ioctl32.c  saa5249.c           tuner-simple.c
> bttv-gpio.c    cpia2_core.c      tda7432.c           tvaudio.c
> bttv-i2c.c     cpia2_usb.c       tda9875.c           tveeprom.c
> bttv-if.c      cpia2_v4l.c       tda9887.c           wm8739.c
> bttv-input.c   cs53l32a.c        tlv320aic23b.c      wm8775.c
> bttv-risc.c    msp3400-driver.c  tuner-3036.c
config VIDEO_BT848
        tristate "BT848 Video For Linux"
        depends on VIDEO_DEV && PCI && I2C && VIDEO_V4L2

Argh! it should be V4L1 instead!
 

> All these files include v4l2-dev.h and have HAVE_V4L1 defined when V4L1 is
> not turned on in Kconfig.  There files are all buildable when V4L1 is off;
> they don't depend on it in Kconfig. 
Some of the above drivers are V4L2, like tda9887, tuner-core,
tuner-simple, msp3400, cs53l32a, tveeprom, wm87xx. Maybe they are just
including the wrong headers. We should try to change to videodev2.h and
see what happens with all those drivers. The ones that break should me
marked with the proper requirement on Kconfig. 

Some of they need some #ifdef inside. For example, compat_ioctl32 should
handle both APIs, since it is a generic code to fix 32 bit calls to 64
bit kernel.

>  There might be more files which have
> the problem with the defines but don't include v4l2-dev.h, I haven't
> checked for that.
> 
> > > The first thing to solve this that HAVE_V4L1 should die.
> > Partially agreed. We should move all in-kernel stuff to use
> > CONFIG_VIDEO_V4L1_COMPAT. For userspace, this flag might be interesting
> > (as well as his counterpart HAVE_V4L2).
> > > Why have a define that is supposed to mirror a Kconfig variable?
> > Legacy stuff. HAVE_V4L1 came before the Kconfig flag.
> > > If everyone used CONFIG_VIDEO_V4L1_COMPAT then there wouldn't be this problem, which some
> > > code things V4L1 is on, and some code thinks it's off.
> > >
> > > The second thing, is that many drivers don't respect
> > > CONFIG_VIDEO_V4L1_COMPAT.  They include V4L1 code when V4L1 is turned off.
> > >
> > > To fix this completely:
> > > 1. Find all unnecessary includes of videodev.h and remove them.
> > Ok.
> > >
> > > 2. Any remaining includes of videodef.h in drivers which don't depend on
> > >    VIDEO_V4L1_COMPAT or VIDEO_V4L1 in Kconfig should be protected with
> > >    #ifdef CONFIG_VIDEO_V4L1_COMPAT.  This will break many drivers.
> > Instead, we should do the opposite: checking for both flags inside
> > videodev.h. If no V4L1 or V4L1_COMPAT, it should just include
> > videodev2.h.
> 
> Would some drivers continue to include videodev2.h directly?  Or would it
> only be included through videodev.h?
The idea is that V4L2 drivers should need to include only videodev2,
when V4L1 compat is not defined.
> 
> > > 3. Replace HAVE_V4L1 with CONFIG_VIDEO_V4L1_COMPAT everywhere.
> > Agreed.
> > >    This will break many drivers.
> > Perhaps I missed the point, but I can't see what else would be broken by
> > replacing the check.
> 
> See my list above of files in which HAVE_V4L1 is defined but
> CONFIG_VIDEO_V4L1* is not defined.  If you change an #ifdef from HAVE_V4L1
> to CONFIG_VIDEO_V4L1_COMPAT, then that #ifdef is changing from on to off.
> This can breaks things.  Go ahead and try it, you'll see.
So, we need to fix it. May you work on such patch?
> 
> > > 4. Any drivers broken by steps 2 and 3 should be fixed by either:
> > >    A.  Protecting all V4L1 code with #ifdef CONFIG_VIDEO_V4L1_COMPAT
> > >    B.  Making the drivers require V4L1 in Kconfig
> > Broken drivers for V4L2 only should be marked in Kconfig, just like
> > bttv. Of course, we should work to fix it. Nickolay did a patch in the
> > past removing V4L1 code from bttv and make it use v4l1-compat module
> > instead. We should work seriously on such patch.
> 
> Is it possible that a driver might include V4L1 compatilbility code, for
> functionality beyond that which the v4l-compat module can provide?
Yes. There is just *one* ioctl that should be done driver by driver, for
buffer allocation on V4L1 model.

Cheers, 
Mauro.

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