Date: Thu, 29 Jan 2004 11:45:40 +0100 (CET) From: Harti Brandt <brandt@fokus.fraunhofer.de> To: "Kenneth D. Merry" <ken@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: atapi cdrecord under 5.2 Message-ID: <20040129113922.I3841@beagle.fokus.fraunhofer.de> In-Reply-To: <20040128230540.GA89272@panzer.kdm.org> References: <1075254712.2786.42.camel@itouch-1011.prv.au.itouchnet.net> <1075287190.46456.7.camel@pav.hide.vol.cz> <20040128230540.GA89272@panzer.kdm.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, 28 Jan 2004, Kenneth D. Merry wrote: KDM>[ resend from a different address so my post will go through, sorry for the KDM>duplicate ] KDM> KDM>On Wed, Jan 28, 2004 at 11:53:10 +0100, Pav Lucistnik wrote: KDM>> V st, 28. 01. 2004 v 11:07, Harti Brandt p??e: KDM>> KDM>> > That may be the same problem I discovered yesterday together with Joerg KDM>> > Schilling (the cdrecord author). According to him, for several kinds of CD KDM>> > recorders error returns from the recorder are expected by cdrecord (some KDM>> > recorders, for example, return an error for long writes, although they KDM>> > process it (this is allowed by the SCSI spec)). cdrecord handles these KDM>> > error (and they do not turn up as errors to the user), but in order to do KDM>> > this it expectes the CAM layer to return correct sense data after an error KDM>> > (the CAM spec requires the CAM layer to automatically issue a SENSE KDM>> > command after errors). As you can see in the above output, the sense data KDM>> > is all zero, which seems to be broken. At the moment it's not clear, where KDM>> > the problem exactly is: CAM, ATAPICAM or ATAPI. KDM>> KDM>> Since ATAng commit sense bytes are no longer automatically filled on KDM>> error conditions. This very regression was worked around in recent KDM>> growisofs (I did the testing for author). If you as kernel developer KDM>> could try looking into it that would be great... KDM> KDM>Since ATAPICAM doesn't do autosense itself, the error recovery code has to KDM>issue the request sense command. (That code was actually somewhat broken KDM>initially, since every other driver requests sense for a failed command. KDM>So ATAPICAM was the first SIM driver not to do it.) ATAPICAM does autosense, it's just commented out, because of a bad interaction with ATAng. KDM>By default, though, commands that are issued through the pass(4) driver KDM>(like the commands from cdrecord) do not go through the error recovery KDM>code. You have to set the CAM_PASS_ERR_RECOVER flag on the CCB to enable KDM>error recovery. (And set the retry count appropriately.) KDM> KDM>For cdrecord, enabling error recovery in the kernel for its commands is KDM>probably not desirable. It probably needs to see errors and deal with KDM>them. KDM> KDM>So we've got two basic choices: KDM> - modify cdrecord, and other applications, to look for the KDM> CAM_AUTOSNS_VALID status flag on a failed CCB and issue the request KDM> sense command if necessary. KDM> - modify ATAPICAM to do autosense. KDM> KDM>The latter would probably be the easiest for application developers to deal KDM>with. Yes, and it is the only reliable way. The problem is that you need to sense as soon as the error happens - the drive must stop processing queued commands and the driver must stop queueing new commands to the driver until it has reported sense data. If you put the processing in the user process, the driver must cause the driver to continue processing as soon as the driver has returned an error, because it cannot know, whether the application will sense or not. If there are other commands to the driver in the queues, the sense data will simply be lost and the application will see junk. So this is only reliable if you ensure that only one processing is giving commands on a given drive, which generally you don't want to do. Also the CAM standard is very clear on this. harti KDM> KDM>I assume that you fixed growisofs by using the first method. KDM> KDM>Ken -- harti brandt, http://www.fokus.fraunhofer.de/research/cc/cats/employees/hartmut.brandt/private brandt@fokus.fraunhofer.de, harti@freebsd.org
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20040129113922.I3841>