Messages in this thread | | | Date | Fri, 26 May 2006 12:01:15 -0400 | From | "Jon Smirl" <> | Subject | Kernel design: support for multiple local users |
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A central, unanswered question in the graphics debate is whether the kernel should directly support multiple users logged into video cards. Currently this is not supported. A simple example of this is a two headed video card and two keyboards. Should the kernel support two independent users logged into these heads and give them the ability to control their environment without needing to be root?
This situation commonly occurs in Internet cafes, kiosks, schools, etc. There are several out of tree patches addressing this. I also believe there are multiple vendors selling products in this configuration.
It is possible to set the current X server up to support this configuration. Using the X server this way has some drawbacks. The X server needs to be run as root. The multiple users are sharing a single X server image so things they do can impact the other users. Plus this solution only works for X apps. Things like VT swap must be disabled.
An alternative model with kernel support would work something like this. Devices are created for each video head. Devices (video, mouse, keyboard, usb ports, cdrom, etc) are marked as belonging in a console grouping. When you log in ownership of the grouped devices is assigned to you.
Now that you have ownership of the devices you are able to control them without being root. If you want to change your video mode ask your video device to do it (this is not a comment on how the video device achieves the mode change). Since the devices are locally owned each user can independently run X, emacs, svglib or whatever.
I am obviously leaving out some details about how sharing the resources of a single video card between heads is achieved. If you prefer, think of this scenario for two installed graphics cards. This is not an attempt to detail how to build the feature.
The question is, do we want local multiuser support in the kernel, or should it be an application feature?
-- Jon Smirl jonsmirl@gmail.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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