Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [RFC][PATCH] input: Introduce device information ioctl | Date | Tue, 7 Dec 2010 13:55:08 +0100 |
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On Tuesday 07 December 2010, Kay Sievers wrote: > >> Oh, how does that work? With the ioctl call, userspace has to supply > >> the size it expects to be returned from the kernel. How does the > >> kernel otherwise know how much it is allowed to copy to the user? > > > > The ioctl command number itself is calculated from the size of the > > data that gets passed: > > > > #define EVIOCGDEVINFO _IOR('E', 0x09, struct input_devinfo) > > > > If struct input_devinfo ever changes (which it can, but should not), > > the command changes as well. > > So unlike statet, it's not extensible, and this struct and this ioctl > can never change?
Exactly. We have plenty of unused ioctl numbers free though.
Arnd
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