From: Andrew Morton <akpm@osdl.org>
To: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Cc: Reinette Chatre <reinette.chatre@linux.intel.com>,
Joe Korty <joe.korty@ccur.com>, Paul Jackson <pj@sgi.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer
Date: Wed, 4 Oct 2006 18:57:47 -0700 [thread overview]
Message-ID: <20061004185747.4cb64048.akpm@osdl.org> (raw)
In-Reply-To: <200610041833.40866.inaky@linux.intel.com>
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.
next prev parent reply other threads:[~2006-10-05 1:57 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-10-05 0:56 [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer Reinette Chatre
2006-10-05 1:10 ` Andrew Morton
2006-10-05 1:33 ` Inaky Perez-Gonzalez
2006-10-05 1:57 ` Andrew Morton [this message]
2006-10-05 19:49 ` [PATCH] bitmap: parse kernel and user buffers Reinette Chatre
2006-10-05 21:48 ` [PATCH] bitmap: parse input from " Reinette Chatre
2006-10-05 22:32 ` Inaky Perez-Gonzalez
2006-10-05 1:40 ` [PATCH] bitmap: separate bitmap parsing for user buffer and kernel buffer H. Peter Anvin
2006-10-05 19:57 ` Andi Kleen
2006-10-05 20:38 ` Andrew Morton
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