watchdog ioctl inconsistencies

watchdog ioctl inconsistencies

[Rasmus Villemoes]

Hi,

uapi/linux/watchdog.h has these

#define WDIOC_SETOPTIONS        _IOR(WATCHDOG_IOCTL_BASE, 4, int)

This is a write from userspace perspective, so should have been _IOW.

#define WDIOC_KEEPALIVE         _IOR(WATCHDOG_IOCTL_BASE, 5, int)

This one doesn't actually take an argument, so should just have been an
_IO - or if anything, an _IOW. One could be misled to think that if the
int argument has 'V' somewhere (perhaps first or last byte, depending on
endianness) that would count as a magic close.

#define WDIOC_SETTIMEOUT        _IOWR(WATCHDOG_IOCTL_BASE, 6, int)
#define WDIOC_SETPRETIMEOUT     _IOWR(WATCHDOG_IOCTL_BASE, 8, int)

The SETTIMEOUT handling does fall through to the GETTIMEOUT case, so
that one is indeed a "write this, but tell me what value actually took
effect". The SETPRETIMEOUT case ends with a break, so that one is really
_IOW.

There's not much to do about these, I think, but perhaps one could add a
comment to the uapi header containing the magic explains-all phrase
"historical reasons".

Does any static checker actually know about these conventions and peek
inside the _IO*() macros when used as an argument to ioctl(), comparing
the type and constness of the third argument to the direction/type
implied by the macro?

Rasmus

Re: watchdog ioctl inconsistencies

[Guenter Roeck]

On 8/26/19 5:54 AM, Rasmus Villemoes wrote:
> Hi,
> 
> uapi/linux/watchdog.h has these
> 
> #define WDIOC_SETOPTIONS        _IOR(WATCHDOG_IOCTL_BASE, 4, int)
> 
> This is a write from userspace perspective, so should have been _IOW.
> 
> #define WDIOC_KEEPALIVE         _IOR(WATCHDOG_IOCTL_BASE, 5, int)
> 
> This one doesn't actually take an argument, so should just have been an
> _IO - or if anything, an _IOW. One could be misled to think that if the
> int argument has 'V' somewhere (perhaps first or last byte, depending on
> endianness) that would count as a magic close.
> 
> #define WDIOC_SETTIMEOUT        _IOWR(WATCHDOG_IOCTL_BASE, 6, int)
> #define WDIOC_SETPRETIMEOUT     _IOWR(WATCHDOG_IOCTL_BASE, 8, int)
> 
> The SETTIMEOUT handling does fall through to the GETTIMEOUT case, so
> that one is indeed a "write this, but tell me what value actually took
> effect". The SETPRETIMEOUT case ends with a break, so that one is really
> _IOW.
> 
> There's not much to do about these, I think, but perhaps one could add a
> comment to the uapi header containing the magic explains-all phrase
> "historical reasons".
> 
Those ioctls were imported into git when the git repository was created.
I don't think it is worth bothering about it now. I also don't think it
would add much if any value to add "historic reason" comments.

Guenter