Re: Ada OS Kernel features

[dmitry@elros.cbb-automation.de (Dmitry Kazakov)]

On 7 Sep 2001 08:18:21 GMT, d97svema@dtek.chalmers.se (Mattias
Svensson) wrote:

>In article <3b987e18.2182875@news.cis.dfn.de>, Dmitry Kazakov wrote:
>>On Thu, 6 Sep 2001 19:06:29 +0100, "chris.danx"
>><chris.danx@ntlworld.com> wrote:
>>Any shared device should be not allowed to be directly used in the
>>user mode. If a video driver operates in the user mode, then it is
>>possible to have an application that reads and updates the parts of
>>the screen of another application. Now consider that another
>>application is a part of home-banking software. Wellcome in the
>>MS-Windows world!
>
>Why? If the video driver has exclusive access to the video memory and
>just presents an API to other programs by some menas of IPC.

If the driver runs on the context of the caller's process, then there
is no way to share the device safely.

>In what
>way is this different from having the video driver in the kernel? 

Not in the kernel, but in a separate process which has other
privilegies than the caller. There IMO should be no monolitic kernel,
but a set of objects having no more access than they should.

>The hard part I think is to give access to the video memory from
>userspace.

Regards,
Dmitry Kazakov