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Re: IO space memcpy support for userspace.

From: "Dave Airlie" <airlied at gmail dot com>
To: "Roland McGrath" <roland at redhat dot com>
Cc: "linux-kernel at vger dot kernel dot org" <linux-kernel at vger dot kernel dot org>, libc-alpha at sources dot redhat dot com
Date: Sat, 6 Dec 2008 16:30:24 +1000
Subject: Re: IO space memcpy support for userspace.
References: <21d7e9970812041940h29994c60w3e7bcf20b96efe04@mail.gmail.com> <20081205202746.7DB20FC379@magilla.sf.frob.com>

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
>

References:
- IO space memcpy support for userspace.
  - From: Dave Airlie
- Re: IO space memcpy support for userspace.
  - From: Roland McGrath

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