Re: [PATCH] tty add compat_ioctl

[Paul Fulghum <paulkf@microgate.com>]

Arnd Bergmann wrote:
> - The return value of the new compat_ioctl methods should probably
> 'int', not 'long'. We've had the discussion before and then
> decided not to change the existing compat_ioctl and 
> unlocked_ioctl functions -- even though int is more appropriate,
> but having the same prototype has the advantage that a driver
> can use the same function for both ->ioctl and ->compat_ioctl
> if all calls are compatible.

I noticed that but thought the change in return value type
had some higher purpose I had not perceived. If it can be int
that would be the way to go.

> - In your driver you don't get the big kernel lock in the 
> compat_ioctl function. I assume that this is correct for
> the particular driver, but it may be nice if you could
> consequently also add an unlocked_ioctl function that can
> be used without the BKL for native ioctls. It would be good
> to hear an opinon on this from someone who has an insight
> in tty locking issues though, so I'm Cc:ing some people
> who have touched that recently.

I don't count on higher level locking for
synchronization issues specific to the driver.

I thought the current compat_ioctl() was already
meant to *not* have the BKL just like unlocked_ioctl.
My thought was that any driver getting a recent update
like compat_ioctl() would need to be reviewed for BKL
safety and take the lock manually if necessary.

Drivers that are falling behind wont have a compat_ioctl
defined at all.

--
Paul