linux-kernel - Re: UBI/DVB ioctl conflict?

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Message-Id: <200812081041.14178.laurentp@cse-semaphore.com>
Date:	Mon, 8 Dec 2008 10:41:13 +0100
From:	Laurent Pinchart <laurentp@...-semaphore.com>
To:	linux-mtd@...ts.infradead.org, dedekind@...radead.org
Cc:	Josh Boyer <jwboyer@...ux.vnet.ibm.com>,
	v4l-dvb-maintainer@...uxtv.org,
	LKML <linux-kernel@...r.kernel.org>, arnd@...db.de
Subject: Re: UBI/DVB ioctl conflict?

Hi,

On Monday 08 December 2008 07:20:26 Artem Bityutskiy wrote:
> On Sun, 2008-12-07 at 09:58 -0500, Josh Boyer wrote:
> > I received a bug report where someone noticed that the UBI ioctls can
> > conflict with the dvb subsystem.  Looking it over, it seems that both
> > subsystems use 'o' as the magic, and do have a set of somewhat
> > conflicting sequence numbers as the secondary arg.
> >
> > Is this a problem?
>
> Hmm, thanks for noticing.
>
> I've looked at this, and thankfully it looks like we were lucky and do
> not use the same 'ioctl()' numbers, by chance.
>
> Ioctl number has the following structure:
>
> bits 0-15: command (or sequence number)
> bits 16-29: parameter size
> bits 30-31: mode (read, write, etc).
>
> We have the following overlaps with DVB subsystem:
>
> #define AUDIO_STOP   _IO('o', 1)
> #define UBI_IOCRMVOL _IOW('o', 1, int32_t)
>
> #define AUDIO_PLAY   _IO('o', 2)
> #define UBI_IOCRSVOL _IOW('o', 2, struct ubi_rsvol_req)
>
> #define AUDIO_PAUSE  _IO('o', 3)
> #define UBI_IOCRNVOL _IOW('o', 3, struct ubi_rnvol_req)
>
> These are fine because parameter sizes are different, and because UBI
> uses _IOW and DVB uses _IO, so the mode bits are "01" and "00".
>
> And:
>
> #define FE_DISEQC_RECV_SLAVE_REPLY _IOR('o', 64,
>                                         struct dvb_diseqc_slave_reply)
> #define UBI_IOCATT _IOW('o', 64, struct ubi_attach_req)
>
> #define FE_DISEQC_SEND_BURST _IO('o', 65)
> #define UBI_IOCDET _IOW('o', 65, int32_t)
>
> are also fine because parameter sizes are different and the mode bits
> are different.
>
> However, we have to be very careful in the future. It seems like DVB
> has been in the kernel long before UBI, so this potential conflict
> would be my fault.
>
> Neither DVB nor UBI seem not to be documented in
> Documentation/ioctl/ioctl-number.txt. Should we do this?
>
> P.S. Added Arnd to CC for suggestions, as well as LKML and DVB
> maintainers.

Correct me if I'm wrong, but doesn't this only matters for devices that would 
implement both the UBI and DVB API on the same inode ? That would be quite 
unlikely.

Best regards,

-- 
Laurent Pinchart
CSE Semaphore Belgium

Chaussee de Bruxelles, 732A
B-1410 Waterloo
Belgium

T +32 (2) 387 42 59
F +32 (2) 387 42 75
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