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Message-ID: <21d7e9970812052230j705fc9bfi4a659378a43ca240@mail.gmail.com>
Date: Sat, 6 Dec 2008 16:30:24 +1000
From: "Dave Airlie" <airlied@gmail.com>
To: "Roland McGrath" <roland@redhat.com>
Subject: Re: IO space memcpy support for userspace.
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       libc-alpha@sources.redhat.com
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	 <20081205202746.7DB20FC379@magilla.sf.frob.com>
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On Sat, Dec 6, 2008 at 6:27 AM, Roland McGrath <roland@redhat.com> wrote:
> There is never going to be something in memcpy that makes any magical
> kernel calls to find out about an address.  That's just loony, sorry.
> memcpy is inlined away by the compiler in good cases.  It's like you'd
> asked for "*ptr" to have magical constraints by the compiler generating
> code to ask the kernel if "ptr" is a special address.  Uh, really?
>

Yeah I didn't think it was a good idea, its what HPUX does, so that
implied it probably wasn't a good idea.

I was just hoping it might help people come up with a good idea.

Dave.

> If you can think of an efficient way to determine it and do what you need,
> then you could write optimized routines that do that in the vDSO perhaps.
>
>
> Thanks,
> Roland
>
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