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    SubjectRe: [patch 6/7] um: Convert mmapper to unlocked_ioctl
    On Thu, 15 Oct 2009, Arnd Bergmann wrote:

    > On Thursday 15 October 2009, Thomas Gleixner wrote:
    > > The ioctl is empty and needs no serialization. We might remove it
    > > completely but that would change the return value from -ENOIOCTLCMD to
    > > -ENOTTY.
    > >
    > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    > > Cc: Jeff Dike <jdike@addtoit.com>
    >
    > This one is tricky if you want to get it right according to the
    > book. ENOIOCTLCMD is never a valid return code for user space,
    > but sys_ioctl passes it down anyway.
    >
    > However, returning -ENOIOCTLCMD from an *unlocked_ioctl* function
    > automatically gets turned into -EINVAL. It does this to allow
    > the same functions to be used for unlocked_ioctl and compat_ioctl.
    > In effect, this patch is functionally identical to removing the
    > ioctl function, which I think is what should be done here.

    Yeah, we get either -ENOTTY or -EINVAL which always changes the user
    space return value. So yes, removing it at least saves some line of
    code :)

    Thanks,

    tglx


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