linux-kernel - Re: [PATCH] [media] v4l2 core: return -ENOIOCTLCMD if an ioctl doesn't exist

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Date:	Mon, 27 Jun 2011 18:14:35 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Mauro Carvalho Chehab <mchehab@...hat.com>
Cc:	Hans Verkuil <hverkuil@...all.nl>,
	Sakari Ailus <sakari.ailus@....fi>,
	Linux Media Mailing List <linux-media@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] [media] v4l2 core: return -ENOIOCTLCMD if an ioctl  doesn't exist

On Monday 27 June 2011, Mauro Carvalho Chehab wrote:
> > The point is that the spec can easily be improved to make such 'NOP' operations
> > explicit, or to require that if a capability is present, then the corresponding
> > ioctl(s) must also be present. Things like that are easy to verify as well with
> > v4l2-compliance.
> 
> We currently have more than 64 ioctl's. Adding a capability bit for each doesn't
> seem the right thing to do. Ok, some could be grouped, but, even so, there are
> drivers that implement the VIDIOC_G, but doesn't implement the corresponding VIDIO_S.
> So, I think we don't have enough available bits for doing that.

It shouldn't be too hard to do an ioctl command that returns a le_bitmask with the
ioctl command number as an index (0 to 91, currently), and the bit set for each
command that has the corresponding v4l2_ioctl_ops member filled for the device.
That would be an obvious way to query the operations, but I don't know if it's
useful.

	Arnd
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