On Mon, Sep 24, 2018 at 10:18:52PM +0200, Arnd Bergmann wrote: > On Tue, Sep 18, 2018 at 7:59 PM Jason Gunthorpe <jgg@xxxxxxxx> 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@xxxxxxxxxxxxx> > > > > > > > > > > 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 > as well. > > 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 > definition. That could work well, but the first idea could be done globally and mechanically, while this would require very careful per-driver investigation. Particularly if the core code has worse performance.. ie due to kmalloc calls or something. I think it would make more sense to start by having the core do the case to __user and then add another entry point to have the core do the copy_from_user, and so on. Jason
