Date: Thu, 17 Nov 2005 15:29:00 -0800 (PST)
Message-Id: <20051117.152900.72981605.davem@davemloft.net>
To: hugh@veritas.com
Cc: akpm@osdl.org, nickpiggin@yahoo.com.au, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/11] unpaged: get_user_pages VM_RESERVED
From: "David S. Miller" <davem@davemloft.net>
In-Reply-To: <Pine.LNX.4.61.0511171928320.4563@goblin.wat.veritas.com>
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From: Hugh Dickins <hugh@veritas.com>
Date: Thu, 17 Nov 2005 19:29:17 +0000 (GMT)

> The PageReserved removal in 2.6.15-rc1 prohibited get_user_pages on the
> areas flagged VM_RESERVED in place of PageReserved.  That is correct in
> theory - we ought not to interfere with struct pages in such a reserved
> area; but in practice it broke BTTV for one.
> 
> So revert to prohibiting only on VM_IO: if someone gets into trouble
> with get_user_pages on VM_RESERVED, it'll just be a "don't do that".
> 
> You can argue that videobuf_mmap_mapper shouldn't set VM_RESERVED in the
> first place, but now's not the time for breaking drivers without notice.
> 
> Signed-off-by: Hugh Dickins <hugh@veritas.com>

It might be a nice little 2.6.16 project to simplify that
videobuf_mmap_mapper() code, and in fact other driver subsystems want
a similar facility, such as DVB.

So putting some helper routines in the core MM for this, in one spot,
seems like the long term way to handle this peculiar stuff.
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