linux-kernel - Re: [PATCH 1/1] LinuxPPS: Pulse per Second support for Linux

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Message-ID: <20070221120426.GJ4641@enneenne.com>
Date:	Wed, 21 Feb 2007 13:04:26 +0100
From:	Rodolfo Giometti <giometti@...eenne.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, linuxpps@...enneenne.com
Subject: Re: [PATCH 1/1] LinuxPPS: Pulse per Second support for Linux

On Mon, Feb 19, 2007 at 06:56:20PM -0800, H. Peter Anvin wrote:

> It's not a precondition for a file descriptor, either.  There are plenty 
> of ioctl-only device drivers in existence.
> 
> Furthermore, a file descriptor doesn't imply a device entry.  Consider 
> pipe(2), for example.
> 
> As far as the kernel is concerned, a file handle is a nice, uniform 
> system for providing communication between the kernel and user space. 
> It doesn't matter if one can read() or write() on it; it's perfectly 
> normal to support only a subset of the normal operations.

The problem is that sometimes you cannot have a filedescriptor at
all. Think about a PPS source connected with a CPU's GPIO pin. You
have no filedes to use and defining one just for a PPS source or for a
class of PPS sources, I think, is a non sense.

RFC simply doesn't consider the fact that you can have a PPS source
__without__ a filedes connected with, and a single filedes is
considered __always__ connected with a single PPS source.

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti@...eenne.com
Linux Device Driver                             giometti@...dd.com
Embedded Systems                     		giometti@...ux.it
UNIX programming                     phone:     +39 349 2432127
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