Re: [PATCH 2/3] SCSI core and sd: early detection of medium not present

[Alan Stern <stern@rowland.harvard.edu>]

On Thu, 8 Jun 2006, James Bottomley wrote:

> On Tue, 2006-06-06 at 11:31 -0400, Alan Stern wrote:
> > This patch (as695) changes the scsi_test_unit_ready() routine in the
> > SCSI 
> > core to set a new flag when no medium is present.  The sd driver is 
> > changed to use this new flag for reporting -ENOMEDIUM in from the 
> > sd_media_changed method.
> 
> This would appear to be duplicating the struct scsi_disk media_present
> flag.

Correct, although the semantics of the two flags aren't exactly the same.

>  Moving the media_present flag from scsi_disk to scsi_device may
> make a bit of sense long term ... however, there's also dupication with
> the sr driver and the cdrom layer now (that stores media change at the
> cdrom level), so is there an argument why it's better in scsi_device
> than scsi_disk?

I did it that way in the patch because it was the only simple choice.  The 
scsi_test_unit_ready() routine is part of the SCSI core and can be called 
for devices that aren't disks.  Hence any flag it sets cannot be part of 
the scsi_disk structure.

In principle the information could be conveyed in the return value from 
scsi_test_unit_ready() rather than in a static flag.  But the routine has 
several callers and I didn't want to change all of them to recognize a 
-ENOMEDIUM return code.  Now in the long run, perhaps that would be a good 
thing to do.  Or perhaps moving the flag to scsi_device would be better, I 
don't know...

Ultimately this boils down to how you want to represent "No medium 
present" in the SCSI core.  What do you think is the bets way?

Alan Stern

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