Re: [PATCH 01/11] unpaged: get_user_pages VM_RESERVED

David S. Miller
2005-11-17T23:29:00Z

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.