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    SubjectRe: [PATCH] staging: comedi: remove __user annotation inside of struct's
    On 2012-05-09 11:31, Dan Carpenter wrote:
    > On Wed, May 09, 2012 at 11:20:07AM +0100, Ian Abbott wrote:
    >> On 2012-05-09 00:55, H Hartley Sweeten wrote:
    >>> On Tuesday, May 08, 2012 4:41 PM, H Hartley Sweeten wrote:
    >>>> The structs' comedi_insn, coomedi_insnlist, comedi_cmd,
    >>>> comedi_chaninfo, and comedi_rangeinfo are all passed to
    >>>> the kernel from user space using ioctl commands. They
    >>>> are then copied to kernel space using copy_from_user()
    >>>> before the data is passed to the drivers.
    >>>> The __user annotation should not be used with variables
    >>>> inside the struct. This produces a lot of sparse warnings
    >>>> like:
    >>>> warning: dereference of noderef expression
    >>>> Note: This patch exposes some new warnings about different
    >>>> address space. These will be addressed.
    >>> Please ignore this patch.
    >>> It appears the annotations in the struct definitions are correct.
    >> Personally, I think you were on the mark with the patch. It's
    >> better to avoid using __user in comedi.h so it can be used as-is in
    >> user-space.
    > Sparse is useful so we shouldn't break it. I always run sparse over
    > my patches before submission and look at the warnings. Except if
    > they scroll off the page. In that case, I just figure that the
    > author deserves the bugs.
    > We could just do some ifdeferry to fix it for userspace.

    That doesn't help in cases such as 'struct comedi_insn' where the 'data'
    pointer is a user-space pointer in the user-space copy of the object and
    a kernel-space pointer in the kernel-space copy of the object. The only
    fix for that is to have separate "k" versions of the struct or to do a
    load of casting, which is slightly error-prone and makes the code less

    Are there any handy macros for casting pointers to __user pointers,
    something like

    #define _user(p) ((typeof(*(p)) __user *)(p))

    but preferably without the repeated expansion of 'p' in case of

    -=( Ian Abbott @ MEV Ltd. E-mail: <> )=-
    -=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-

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