[ros-kernel] Re: Proposed new (trivial) device driver

[KJK::Hyperion <no...@li...>]

At 03.16 06/11/2001 +0200, you wrote:
> > More a programming exercise than an actual device driver, yet I haven't
> > seen something like this yet for Windows NT: it's a zero stream
>I do not know if related, but there is a device called null in Win2000, you
>have to enable "Show hidden devices" in the device manager to see it.

Null is the so-called "bit bucket": always returns EOF, zero bytes read 
when you try to read from it, always return OK, all bytes written (but 
actually they aren't written anywhere - the buffer is left untouched) when 
you try to write to it. Zero, instead, is a continuous stream of binary 
zeros. It's very handy when you need to initialize a binary file with the 
contents of another file, but you don't want to put any special data, just 
zero's. For example:

dd if=\\.\ZERO of=\\.\A:
(dd is a standard Unix command - it copies blocks from and to files and 
devices)

erases the contents of the dos device A: (usually \Device\Floppy0) 
overwriting them with zero's

dd if=\\.\ZERO of=\\.\C: bs=512 seek=1

erases the dos device C:, except the first 512 bytes (the boot record if C: 
is a hard disk)

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