Hi Mauro,
On Thursday 08 July 2010 15:51:33 Mauro Carvalho Chehab wrote:
> Em 08-07-2010 09:08, Laurent Pinchart escreveu:
> > On Wednesday 07 July 2010 22:53:40 Mauro Carvalho Chehab wrote:
> >> Em 07-07-2010 16:44, Laurent Pinchart escreveu:
> >>> On Wednesday 07 July 2010 16:58:01 Mauro Carvalho Chehab wrote:
> >>>> Em 07-07-2010 08:53, Laurent Pinchart escreveu:
[snip]
> >>>>> +static long subdev_ioctl(struct file *file, unsigned int cmd,
> >>>>> + unsigned long arg)
> >>>>> +{
> >>>>> + return video_usercopy(file, cmd, arg, subdev_do_ioctl);
> >>>>
> >>>> This is a legacy call. Please, don't use it.
> >>>
> >>> What should I use instead then ? I need the functionality of
> >>> video_usercopy. I could copy it to v4l2-subdev.c verbatim. As
> >>> video_ioctl2 shares lots of code with video_usercopy I think
> >>> video_usercopy should stay, and video_ioctl2 should use it.
> >>
> >> The bad thing of video_usercopy() is that it has a "compat" code, to fix
> >> broken definitions of some iotls (see video_fix_command()), and that a
> >> few drivers still use it, instead of video_ioctl2.
> >
> > video_ioctl2 has the same compat code.
>
> Yes, in order to avoid breaking binary compatibility with files compiled
> against the old videodev2.h header that used to declare some ioctls as:
[snip]
> This doesn't make sense for subdev, as old binary-only applications will
> never use the legacy ioctl definitions.
>
> Probably, we can mark this legacy support for removal at
> Documentation/feature-removal-schedule.txt, and remove
> it on a latter version of the kernel. It seems that the old ioctl
> definitions are before 2005 (before 2.6.12):
Good idea.
[snip]
> > What about renaming video_usercopy to __video_usercopy, adding an
> > argument to enable/disable the compat code, create a new video_usercopy
> > that calls __video_usercopy with compat code enabled, have video_ioctl2
> > call __video_usercopy with compat code enabled, and having subdev_ioctl
> > call __video_usercopy with compat code disabled ?
>
> Seems good, but maybe the better is to put the call to video_fix_command()
> outside the common function.
Agreed. It belongs to video_usercopy and video_ioctl2.
> We may add also a printk for the video_usercopy wrapper printing that the
> driver is using a legacy API call, and that this will be removed on a next
> kernel version. Maybe this way, people will finally submit patches porting
> the last remaining drivers to video_ioctl2.
>
> I suspect, however, that we'll end by needing a subdev-specific version of
> __video_usercopy, as we add new ioctls to subdev.
If we need one then I'll create one in v4l2-subdev.c, but as long as we don't
there's little point in duplicating the code.
I've had a look at video_usercopy and video_ioctl2, and the functions are
mostly identical. The differences are
- video_ioctl2 passes the original arg argument to __video_do_ioctl for _IO
ioctls. video_usercopy passes NULL. This seems to be used by the ivtv driver
to handle DVB _IO ioctls (VIDEO_SELECT_SOURCE, AUDIO_SET_MUTE,
AUDIO_CHANNEL_SELECT and AUDIO_BILINGUAL_CHANNEL_SELECT) that pass an integer
through the ioctl argument. Any objection against passing the original
argument to the ioctl handler in video_usercopy as well ? I've quickly checked
the video_usercopy users and none of them seem to check that arg is NULL for
_IO ioctls. This should thus be harmless.
- For argument of known ioctls that have a few input fields at the beginning
of the structure followed by output fields, video_ioctl2 only copies the input
fields from userspace and zeroes out the rest. video_usercopy doesn't. Do we
have video_usercopy drivers that abuse the output fields to pass information
to the driver, or could the video_ioctl2 behaviour be generalized to
video_usercopy ?
If the answer to the two questions is yes, video_usercopy and video_ioctl2
could use the same code. Otherwise they can't, and in that case I should
probably use video_usercopy in v4l2-subdev.c, replacing it with a private copy
when it will disappear.
--
Regards,
Laurent Pinchart
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