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

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Wed, 2011-08-03 at 17:31 -0500, Mike Christie wrote:
> 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.

The SCSI standard requires all SCSI devices to return UA after a reset
(that's the reason for the code).  So, if I put this patch in, every
removable device would be flagged as having changed media if we go into
an error handling situation and reset it.  I don't think that's a good
idea to fix a single non-standard CD.

James