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Re: O_DIRECT address restrictions

from [Andrew Morton] [Permanent Link][Original]
To: "Rick Smith" <rgsmith72@xxxxxxxxxxx>
Subject: Re: O_DIRECT address restrictions
From: Andrew Morton <akpm@xxxxxxxxx>
Date: Thu, 15 May 2003 18:32:48 -0700
Cc: linux-xfs@xxxxxxxxxxx
In-reply-to: <Sea2-F35IOvGqI3vMLc0000f253@xxxxxxxxxxx>
References: <Sea2-F35IOvGqI3vMLc0000f253@xxxxxxxxxxx>
Sender: linux-xfs-bounce@xxxxxxxxxxx 
"Rick Smith" <rgsmith72@xxxxxxxxxxx> wrote:
>
>      What are the memory address restrictions when using the O_DIRECT flag 
> with XFS? I am trying to perform I/O directly from the filesystem to a piece 
> of mmap'ed video memory and I get the "bad address" error when I attempt to 
> do so with O_DIRECT.

It cannot be done - O_DIRECT only supports IO against legitimate RAM
(memory which is described by the pageframes in mem_map[]).
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