sr.c media_changed handling

From: Dan Dennedy (dan_at_dennedy.org)
Date: 01/07/05

  • Next message: B: "Re: [2.6 patch] net/ipv6/: misc cleanups" 
    To: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Date:	Thu, 06 Jan 2005 22:00:20 -0500

    I am working with a PowerFile DVD jukebox (firewire/sbp2) on kernel
    2.6.10, and it works quite well except for media change handling. The
    problem is sr limits reads of subsequent discs to the capacity of the
    first disc opened. If I remove the line "if (cd->needs_sector_size)"
    from sr_open() and make it always get the capacity when a disc is
    opened, then it resolves my issues. Alternatively, I can send a
    CDROM_MEDIA_CHANGED ioctl when no disc is loaded to force a Read
    Capacity request when the next disc is mounted and opened. I have
    another, non-changer sbp2 disc drive that does not exhibit this problem.
    Therefore, I have two questions:

    1) How does a SCSI device that reports media-changed capable
    (CDC_MEDIA_CHANGED) actually send that signal or flag? Does it come up
    through block device operation media_changed, or is that just a means to
    query the driver's current status?

    2) I suspect there are other devices that have a similar flaw. What is
    the harm in sending an inexpensive Read Capacity command each time a
    disc is opened? IOW, removing that line from sr.c in bitkeeper. It seems
    it would improve compatibility for less well-behaved devices with
    little-to-no impact on the majority.

    p.s. please include my address in the reply; I am not subscribed.

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