Date: Thu, 16 Mar 2006 17:46:53 +0000 (GMT)
From: Hugh Dickins <hugh@veritas.com>
To: "Bryan O'Sullivan" <bos@pathscale.com>
cc: Roland Dreier <rdreier@cisco.com>, Andrew Morton <akpm@osdl.org>,
       torvalds@osdl.org, hch@infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 10 of 20] ipath - support for userspace apps using core
 driver
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On Thu, 16 Mar 2006, Bryan O'Sullivan wrote:
> On Wed, 2006-03-15 at 21:54 -0800, Roland Dreier wrote:
> 
> > How about the case where one wants to map pages from
> > dma_alloc_coherent() into userspace?
> 
> This is precisely our case, btw.  The pages in question are allocated
> during fops->open (some during dev->probe).  mmap and nopage never
> allocate anything.
> 
> >   It seems one should do
> > get_page() in .nopage, and then the driver can do dma_free_coherent()
> > when the vma is released.
> 
> If that were the case, I'm unclear on how I would do this.  Add a
> vmops->close method along with the existing vmops->nopage handler?

If neither mmap nor nopage allocated something, then vmops->close
would be the wrong point at which to free it, I think.

If dev->probe allocated something, module unload would be the right
point to free it.  If fops->open allocated something, fops->release
would be the right point to free it.

I think.  Beware, I've never written a Linux driver, and may well
have this wrong or oversimplified: in which case, I'll have annoyed
someone enough for them to correct me very soon.

Hugh
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