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    SubjectRe: [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer
    On Wed, 4 Oct 2006 18:33:37 -0700
    Inaky Perez-Gonzalez <inaky@linux.intel.com> wrote:

    > On Wednesday 04 October 2006 18:10, Andrew Morton wrote:
    > > On Wed, 4 Oct 2006 17:56:30 -0700
    > > Reinette Chatre <reinette.chatre@linux.intel.com> wrote:
    > > > + if (is_user) {
    > > > + if (__get_user(c, buf++))
    > > > + return -EFAULT;
    > > > + }
    > > > + else
    > > > + c = *buf++;
    > >
    > > Is this actually needed? __get_user(kernel_address) works OK and (believe
    > > it or not, given all the stuff it involves) boils down to a single
    > > instruction.
    >
    > We weren't too sure if that'd be true in all kinds of arches and
    > memory models. If it works for kernel space too, then we can fold
    > out a lot of code...

    We use __get_user() in this fashion in several places in core kernel
    already, although it's usually to find out "will this address give me a
    fault", rather than to actually read a value.

    There's some precedent for the `is_user' approach as well - it has the
    advantage of being more sparse-friendly, and perhaps clearer to read.
    -
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