Messages in this thread |  | | | Date | Wed, 4 Oct 2006 18:57:47 -0700 | | From | Andrew Morton <> | | Subject | Re: [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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