Re: [linux-usb-devel] [2.6-test] Bug in usb-storage or scsi?

From: Alan Stern (stern_at_rowland.harvard.edu)
Date: 09/09/03

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    Date:	Tue, 9 Sep 2003 16:51:06 -0400 (EDT)
To: Georgi Chorbadzhiyski <gf@unixsol.org>

    On Tue, 9 Sep 2003, Georgi Chorbadzhiyski wrote:

    > Hello,
    > I was able to access my Music Pen mp3 player using usb-storage driver
    > in 2.4 without any problems. After updating to 2.6 this was not possible
    > anymore. It seems that usb-storage driver in 2.6 detect the device but
    > I was unable to access /dev/sda1. "mount -t vfat /dev/sda1 /mnt" returns
    > this error: "mount: /dev/sda1 is not a valid block device"
    >
    > Under 2.4.21-ck3, sda1 is corectly registered.
    >
    > Please see the attached files containing dmesg snippets from 2.4 and 2.6
    > kerneles as well as 2.6 config. If you need more information I'll be glad
    > to provide it.
    >
    > The 2.4 kernel that I tested was 2.4.21-ck3
    > The 2.6 kernel that I tested was 2.6.0-test5-mm1, 2.6.0-test4 and 2.6.0-test1

    More problems with that stupid MODE-SENSE cache page! There are so many
    USB storage devices that have problems with that -- I wonder if it's worth
    the effort to try to continue supporting it?

    Georgi, the problem is with your mp3 player, not usb-storage or SCSI.
    It's crashing when given a perfectly legal SCSI command. Linux 2.4
    doesn't issue the command; that's why it works okay.

    If you want a temporary fix for 2.6.0, you can do this: Edit the
    routine sd_read_cache_type in the file drivers/scsi/sd.c (near line 1100).
    Get rid of (or #ifdef out) most of the function; just leave the last few
    lines where it does:

                    printk(KERN_ERR "%s: assuming drive cache: write through\n",
                           diskname);
                    sdkp->WCE = 0;
                    sdkp->RCD = 0;

    You might want to change the KERN_ERR to KERN_NOTICE.

    However, you might also want to think twice before doing this if you have
    any other SCSI disks, because making this change will affect all of them.

    Alan Stern

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