On Tue, Sep 18, 2018 at 7:59 PM Jason Gunthorpe <jgg(a)ziepe.ca> wrote:
On Tue, Sep 18, 2018 at 10:51:08AM -0700, Darren Hart wrote:
> On Fri, Sep 14, 2018 at 09:57:48PM +0100, Al Viro wrote:
> > On Fri, Sep 14, 2018 at 01:35:06PM -0700, Darren Hart wrote:
> > > Acked-by: Darren Hart (VMware) <dvhart(a)infradead.org>
> > >
> > > As for a longer term solution, would it be possible to init fops in such
> > > a way that the compat_ioctl call defaults to generic_compat_ioctl_ptrarg
> > > so we don't have to duplicate this boilerplate for every ioctl fops
> > > structure?
> > Bad idea, that... Because several years down the road somebody will add
> > an ioctl that takes an unsigned int for argument. Without so much as looking
> > at your magical mystery macro being used to initialize file_operations.
> Fair, being explicit in the declaration as it is currently may be
> preferable then.
It would be much cleaner and safer if you could arrange things to add
something like this to struct file_operations:
long (*ptr_ioctl) (struct file *, unsigned int, void __user *);
Where the core code automatically converts the unsigned long to the
void __user * as appropriate.
Then it just works right always and the compiler will help address
Al's concern down the road.
I think if we wanted to do this with a new file operation, the best
way would be to do the copy_from_user()/copy_to_user() in the caller
We already do this inside of some subsystems, notably drivers/media/,
and it simplifies the implementation of the ioctl handler function
significantly. We obviously cannot do this in general, both because of
traditional drivers that have 16-bit command codes (drivers/tty and others)
and also because of drivers that by accident defined the commands
incorrectly and use the wrong type or the wrong direction in the