linux-kernel - Re: [PATCH 1/1] Implement /dev/byte (a generic byte source similiar to /dev/zero)

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Message-ID: <20110420105754.GA14722@ucw.cz>
Date:	Wed, 20 Apr 2011 12:57:55 +0200
From:	Pavel Machek <pavel@....cz>
To:	Alexander Holler <holler@...oftware.de>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Implement /dev/byte (a generic byte source
 similiar to /dev/zero)

On Mon 2011-04-18 13:37:56, Alexander Holler wrote:
> This device outputs by default 0xff instead 0 which makes more sense
> than 0 to clear e.g. FLASH based devices.

Well, now you should provide example where you mmap /dev/byte, then
write() the flash directly from the mapping.

... hmm, that brings good question: what happens on existing mappings
when the byte is changed?

> To make the device more general usable, the value it outputs is changeable
> on a per file descriptor basis through simple writes to it.
> Values can be decimal (0 - 255), octal (00 - 0377) or hex (0x0 - 0xff).
> For other values (or strings) written to it, the write operation returns an
> error and the subsequent output is undefined.
...
>  # Create a file of size 10GB and filled with 0xaa.
> exec 5<>/dev/byte # Open /dev/byte and assign fd 5 to it
> echo 0xaa >&5     # Instruct the device to output 0xaa

That's seriously strange. /dev/byte should be changeable... by writing
bytes.
									Pavel
-- 
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