Re: ioctls, etc. (was Re: [PATCH 1/4] sas: add flag for locally a ttached PHYs)

[Matthew Wilcox]

On Fri, Oct 21, 2005 at 08:32:25AM -0400, Bagalkote, Sreenivas wrote:
> >Jeff Garzik wrote:
> >> Do you know where there are some clear guidelines on the use of 
> >> pointers in a structure passed to an ioctl to lessen (or bypass) 
> >> 32<->64 compat ioctl thunking?
> >
> >Its impossible.  If you pass pointers, you need to thunk.  
> >(Not even passing pointers via sysfs can avoid this.)  
> >Consider running a 32-bit app (with 32-bit pointers and 32-bit 
> >ABI) on a 64-bit kernel.
> 
> The drivers/scsi/megaraid/megaraid_mm.c simply calls regular ioctl
> from within the compat_ioctl, though it does copy to and from the
> userland pointers. This is done by adding appropriate padding.

Yes.  This is what is meant by "thunk".
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