Mailing-List: contact cygwin-help AT sourceware DOT cygnus DOT com; run by ezmlm
List-Subscribe: <mailto:cygwin-subscribe AT sources DOT redhat DOT com>
List-Archive: <http://sources.redhat.com/ml/cygwin/>
List-Post: <mailto:cygwin AT sources DOT redhat DOT com>
List-Help: <mailto:cygwin-help AT sources DOT redhat DOT com>, <http://sources.redhat.com/ml/#faqs>
Sender: cygwin-owner AT sources DOT redhat DOT com
Delivered-To: mailing list cygwin AT sources DOT redhat DOT com
Date: Mon, 5 Feb 2001 17:21:42 +0100
From: Corinna Vinschen <cygwin AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: lseek()/read() to physical drive returning wrong data.
Message-ID: <20010205172142.C15821@cygbert.vinschen.de>
Mail-Followup-To: cygwin AT cygwin DOT com
References: <3A7C4445 DOT B5F8FAB0 AT compaq DOT com> <20010203191915 DOT Z19867 AT cygbert DOT vinschen DOT de>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
User-Agent: Mutt/1.2.5i
In-Reply-To: <20010203191915.Z19867@cygbert.vinschen.de>; from cygwin@cygwin.com on Sat, Feb 03, 2001 at 07:19:15PM +0100

On Sat, Feb 03, 2001 at 07:19:15PM +0100, Corinna Vinschen wrote:
> On Sat, Feb 03, 2001 at 12:47:49PM -0500, Robin T. Miller wrote:
> > Hi All,
> > 	I have a Unix test program named 'dt' which runs with Cygwin.
> > This program tests a variety of devices as well as file systems.  The
> > tests which use lseek() to raw mounted disks, are failing with data
> > compare errors.  It appears either lseek() is positioning incorrectly
> > or read() is returning the wrong data after lseek'ing.
> > 
> > 	This random I/O sequence seems to work correctly to a regular
> > file, so maybe the raw device buffering is messing up?  I'm not sure.
> 
> Lseek on raw devices isn't yet fully implemented. The underlying
> *cough* operating system *cough* isn't able to do a bytewise access
> to the raw device but only in steps of 512 bytes. A full lseek
> implementation would need to do it's own buffering to simulate
> bytewise buffering. This is still missing.

I have just checked in a patch to the Cygwin CVS repository which
should allow bytewise lseek on raw disk devices at least for SEEK_SET
and SEEK_CUR.

For some reason my tests using SEEK_END (aka FILE_END) failed on
my HD partition so using SEEK_END in the current implementation 
results in lseek returning -1 and errno set to EINVAL programatically.

If anybody knows if that observation is correct or if I simply
did something wrong I would gladly appreciate any hint.

Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Developer                                mailto:cygwin AT cygwin DOT com
Red Hat, Inc.

--
Want to unsubscribe from this list?
Check out: http://cygwin.com/ml/#unsubscribe-simple