Re: [RFC PATCH] SCSI: Correct UA being ignored when notifying of media-changed

[Mike Christie <michaelc@cs.wisc.edu>]

On 08/03/2011 05:22 PM, James Bottomley wrote:
> On Wed, 2011-08-03 at 09:39 -0400, Rob Evers wrote:
>> Unit attention commands are getting ignored when a dvd is
>> replaced, resulting in errors when accessing the new dvd.
>>
>> This problem occurred when a system is booted in rescue
>> mode via dvd and the dvd is then replaced with another dvd.
>> Subsequent commands to a filesystem on the dvd, such as
>> 'fsck' and 'restore' report errors.
>>
>> Solution suggested by Mike Christie.
>>
>> Signed-off-by: Rob Evers <revers@redhat.com>
>> ---
>>  drivers/scsi/scsi_error.c |    4 ++++
>>  1 files changed, 4 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
>> index a4b9cdb..725cc11 100644
>> --- a/drivers/scsi/scsi_error.c
>> +++ b/drivers/scsi/scsi_error.c
>> @@ -294,6 +294,10 @@ static int scsi_check_sense(struct scsi_cmnd *scmd)
>>  		 */
>>  		if (scmd->device->expecting_cc_ua) {
>>  			scmd->device->expecting_cc_ua = 0;
>> +				if (sdev->removable) {
>> +					sdev->changed = 1;
>> +					return SUCCESS;
>> +				}
> 
> Are you sure about this?  We only set expecting_cc_ua if the device was
> reset in error handling ... and there we definitely *don't* want to
> trigger a medium change.
> 

What is happening is that we have a quirky device, and when you switch
CD/DVDs the first command times out, so the scsi error handler runs.
That is why the above code was modified. Before the patch the scsi layer
would just retry the IO, and sr would not see the sense and so it would
not detect the media changed. So the above code was meant to work like
UA code in scsi_io_completion.