/dev/io , /dev/mem : only used by Xorg?

Kris Kennaway kris at obsecurity.org
Mon Feb 28 10:57:52 GMT 2005

On Mon, Feb 28, 2005 at 01:32:26AM -0800, Ted Mittelstaedt wrote:

> Instead, they are part of the kernel itself.
> All the /dev files are, /dev/random, /dev/ad0 and so on, are simple
> files that take up only a few bytes of space.  They are convenient
> "hook points" to use to get to these devices.  That is, when a program
> accesses /dev/random, it isn't actually opening that file.  Instead,
> the kernel intercepts that call and supplies the program opening
> that device with the output of the actual device.
> This is why these device files are created with the mknod utility,
> rather than just copying a file to /dev/random - since doing that is
> accessing the device, not creating the device file.
> So, deleting these /dev devices saves you practically no space at
> all, and does not in fact delete the devices - it only deletes the
> access point to them.  The devices are still there in the kernel.

No, in 5.x the device nodes are created automatically by devfs and
only appear in /dev by default if support is enabled in the kernel.
As the original poster discussed, /dev/io, /dev/mem and /dev/random
are optional components of the 5.x kernel, although as I replied, the
situations in which one would not want to include them are limited.

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