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Date: Tue, 18 Apr 2006 17:20:49 +0200
From: Gunther Mayer <gunther.mayer@gmx.net>
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To: Zinx Verituse <zinx@epicsol.org>
CC: lkml <linux-kernel@vger.kernel.org>
Subject: Re: ide-cd.c, "MEDIUM_ERROR" handling
References: <20060418011839.GA10619@atlantis.chaos>
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Zinx Verituse wrote:

>I recently bought a DVD drive which appears to not retry enough when it's
>having trouble reading a disc - I'm requesting an option (or changing the
>default behavior) so that this drive is actually usable with the Linux
>ide-cd drivers - specificly, the code:
>	} else if (sense_key == MEDIUM_ERROR) {
>		/* No point in re-trying a zillion times on a bad
>		 * sector...  If we got here the error is not correctable */
>		ide_dump_status (drive, "media error (bad sector)", stat);
>		do_end_request = 1;
>	}
>needs to be disabled for my drive to read CDs properly.
>
>With this code enabled, no retries are made, and the kernel sees medium errors
>and returns bad data to the application reading; 
>
It would be a kernel bug if it returns bad data. It should return an 
error code to the application.

- The device should implement a decent retry strategy.
- There are special forensic applications which can be tuned to re-read 
bad sectors multiple times if needed.