linux-kernel - Re: IO space memcpy support for userspace.

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Message-Id: <20081205202746.7DB20FC379@magilla.sf.frob.com>
Date:	Fri,  5 Dec 2008 12:27:46 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	"Dave Airlie" <airlied@...il.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	libc-alpha@...rces.redhat.com
Subject: Re: IO space memcpy support for userspace.

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?

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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