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    SubjectRe: [PATCH 08/10] Use __kernel_ulong_t in struct msqid64_ds
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    On Thu, May 17, 2012 at 8:55 PM, H. Peter Anvin <hpa@kernel.org> wrote:
    > On 05/17/2012 08:49 PM, Linus Torvalds wrote:
    >> On Thu, May 17, 2012 at 8:39 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
    >>>
    >>> That will be wrong.   __BITS_PER_LONG defines # bits of long
    >>> as seen by kernel.  We don't use it in user space.
    >>
    >> Yes you do. Exactly in that structure that Peter points to. *Exactly*
    >> because that structure uses "long" instead of some fixed size. Which
    >> will be different in user mode than in kernel mode.
    >>
    >> And if user mode doesn't use these headers at all, then we should stop
    >> playing the insane games.
    >>
    >
    > User mode can, and should, be able to use the exported headers.  David
    > Howells have been doing even more work to distill out the actual
    > exported ABIs from the kernel and remove remaining chaff.
    >
    > That being said it seems kind of loopy to expect something called
    > __BITS_PER_LONG to be anything other than (CHAR_BIT*sizeof(long)),
    > especially since one of the main uses of it seems to be sizing
    > bitvectors (which has its own issues on bigendian machines because I
    > think we do littleendian bit numbering even on bigendian iron).
    >

    But __BITS_PER_LONG used in kernel header files really
    means "long" as seen by kernel, not by user space. 64-bit
    kernel can have 32-bit and 64-bit longs in use space.
    __BITS_PER_LONG is a bad name for user space.


    --
    H.J.
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