On Wed, 25 May 2011, Linus Torvalds wrote:

> On Wed, May 25, 2011 at 12:52 PM, Parag Warudkar <parag.lkml@gmail.com> wrote:
> >
> > +static inline int sdev_early_check(struct scsi_device *sdev)
> > +{
> > +       if (!sdev || sdev->sdev_state == SDEV_DEL
> > +               || sdev->sdev_state > SDEV_QUIESCE)
> > +               return -ENXIO;
> > +       return 0;
> > +}
> 
> Can somebody explain why it's those states, and nothing else?
> 
> Quite frankly, if it's about "don't oops on sdev->queue not existing",
> then test for that. Not for some random and uncommented list of
> states.

List of states and what commands if any are accepeted for each state are 
explained in scsi_device.h enum definition of scsi_device_state : 

enum scsi_device_state {
        SDEV_CREATED = 1,       /* device created but not added to sysfs
                                 * Only internal commands allowed (for 
inq) */
        SDEV_RUNNING,           /* device properly configured
                                 * All commands allowed */
        SDEV_CANCEL,            /* beginning to delete device
                                 * Only error handler commands allowed */
        SDEV_DEL,               /* device deleted 
                                 * no commands allowed */
        SDEV_QUIESCE,           /* Device quiescent.  No block commands
                                 * will be accepted, only specials (which
                                 * originate in the mid-layer) */
        SDEV_OFFLINE,           /* Device offlined (by error handling or
                                 * user request */
        SDEV_BLOCK,             /* Device blocked by scsi lld.  No
                                 * scsi commands from user or midlayer
                                 * should be issued to the scsi
                                 * lld. */
        SDEV_CREATED_BLOCK,     /* same as above but for created devices 
*/
};

In this case - we check for cases where no commands are allowed and reject 
those right away, leaving prep_state_check to do filtering at lower level 
for which commands are allowed and which are not as the state permits.
 
Parag