[RFC / BUG] mtd: provide proper 32/64-bit compat_ioctl() support for BLKPG

[Brian Norris]

On Fri, Aug 28, 2015 at 07:12:36PM -0700, Brian Norris wrote:
> The same bug applies to block/ioctl.c

Actually I'll correct myself: it looks like block/ already has OK
compat_ioctl support for this. Block devices do a copy to/from user
space to marshal a new struct. Personally, I find my approach a little
clearer. 

> But then: which tree should it go in?

I guess since this is only an MTD bug, then it'd be fair to take via
MTD. I'll plan to do that eventually if there are no objections.

> Tested only on MTD, with an ARM32 user space on an ARM64 kernel.
> 
> Signed-off-by: Brian Norris <computersforpeace at gmail.com>
> ---
>  drivers/mtd/mtdchar.c      | 42 +++++++++++++++++++++++++++++++++---------
>  include/uapi/linux/blkpg.h | 10 ++++++++++
>  2 files changed, 43 insertions(+), 9 deletions(-)

I also suspect it might make more sense to move the compat definitions
to a new non-UAPI include/linux/blkpg.h. I'll probably put that in v2.

Brian