linux-kernel - Re: How to avoid data copies in a driver ?

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Message-ID: <20080515135901.GX7577@csclub.uwaterloo.ca>
Date:	Thu, 15 May 2008 09:59:01 -0400
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	Francis Moreau <francis.moro@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: How to avoid data copies in a driver ?

On Thu, May 15, 2008 at 09:44:37AM +0200, Francis Moreau wrote:
> So I would need to map this pointer into the kernel space, then fill it, take
> care of cache coherency, unmap the kernel pointer.
> 
> Do you have any example of that in the kernel tree ?

I was asking if that would work.  Does the to_user and from_user work on
a pointer from user space if that pointer points at a memory mapped
file?

> BTW, data are received in interrupt context. Is it safe to put them in mapped
> memory  (can I have page fault ?) in this context ?

Oh I thought you just wanted user space to be able to ask for a chunk of
data.  I wouldn't want to write to a file in an interrupt handler.
Compared to the disk I/O a memory copy sounds rather insignificant to
the overall process.

-- 
Len Sorensen
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