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    SubjectRe: copy_from_user/copy_to_user question
    Well, sorry for all the questions. I really appreciate
    everybody's help and especially Steve for standing up
    for me!! All the reasons you cited are true and that
    is why I am afraid I cannot post the actual code etc.

    There was never a question in my mind that we have to
    use the *_user functions. I was just trying to
    understand all the corner cases and the semantics of
    how things worked when it has not been used.

    Thanks once again.
    Signing off this thread.
    Vinay


    --- "linux-os (Dick Johnson)" <linux-os@analogic.com>
    wrote:

    >
    > On Tue, 6 Dec 2005, Vinay Venkataraghavan wrote:
    >
    > >
    > > Thanks to Steve and everybody who sent such
    > detailed
    > > and timely responses to my question.
    > >
    > > The motivation for the copy to user question is
    > due to
    > > the handling of ioctl calls in the driver for a
    > chip
    > > that is widely used. I just could not beleive that
    > > they would/could commit such a mistake.
    > >
    > > It looks like the old driver code still seems to
    > work
    > > even without performing copy_to_user and
    > > copy_from_user.
    > >
    > > But this brings about another scenario. What if
    > the
    > > case statement in the ioctl call only needs to
    > have
    > > access to the members of the structure passed in
    > > through the arg pointer but does not need to
    > modify
    > > these values and return values.
    > >
    > > Is this still a problem if copy_to_user and
    > > copy_from_user is not used?
    > >
    > > Thanks,
    > > Vinay
    >
    > If you __access__(note) user-mode data from the
    > kernel, you __must__
    > use the appropriate /copy/to/from/get/put/user
    > functions and/or
    > macros. And, you __must__ not be in a spin-lock, or
    > otherwise have
    > the interrupts disabled, while doing it. There are
    > no exceptions.
    >
    > (note)__assess__ means even "peek at".
    >
    > FYI, there should never even be such a question.
    >
    > Cheers,
    > Dick Johnson
    > Penguin : Linux version 2.6.13.4 on an i686 machine
    > (5589.55 BogoMips).
    > Warning : 98.36% of all statistics are fiction.
    > .
    >
    >
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    >




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