linux-kernel - Re: Question: how to copy to user space from a tasklet

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Message-ID: <4CBC7D62.6040408@s5r6.in-berlin.de>
Date:	Mon, 18 Oct 2010 19:01:22 +0200
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Tom Brown <sa212+emis@...onix.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Yong Zhang <yong.zhang@...driver.com>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: Question: how to copy to user space from a tasklet

Tom Brown wrote:
> Thanks, think I'm there:
> 
> 1 - The user calls mmap() with a specific offset to flag that he wants a
> DMA buffer
> 
> 2 - I then 'vmalloc' the buffer, and call 'setPageReserved' for each page
> 
> I then step over each page, and:
> 
> 3 - call 'vmalloc_to_pfn' to get a PFN for each page, and then
> 
> 4 - call 'remap_page_range' for that page (I instead call
> 'remap_pfn_range' for kernels >= 2.6.10, but I'm on 2.6.9)
> 
> This gives me the buffer, and the interrupt handler then just uses
> 'memcpy' to copy data to the user.

I would have thought of a bunch of alloc_page() and vm_insert_page() but I
don't know if vm_insert_page exists in 2.6.9 and if it honors user limits.

Plus dma_map_page() to get zero-copy operation with a DMA capable device.
-- 
Stefan Richter
-=====-==-=- =-=- =--=-
http://arcgraph.de/sr/
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