Re: slave_destroy called in scsi_scan.c:scsi_probe_and_add_lun()

[Douglas Gilbert <dougg@torque.net>]

Justin T. Gibbs wrote:
> In debugging a different bug in the new 2.5.X port of the aic7xxx driver,
> I came across this behavior in scsi_probe_and_add_lun()
> 
>         /*
>          * Since we reuse the same sdevscan over and over with different
>          * target and lun values, we have to destroy and then recreate
>          * any possible low level attachments since they very will might
>          * also store the id and lun numbers in some form and need updating
>          * with each scan.
>          */
>         if (sdevscan->host->hostt->slave_destroy)
>                 sdevscan->host->hostt->slave_destroy(sdevscan);
>         if (sdevscan->host->hostt->slave_alloc)
>                 sdevscan->host->hostt->slave_alloc(sdevscan);
> 
> So, you cannot rely on slave_destroy as an indication of a device really
> going away in the physical sense.  In SPI, for example, the driver can only
> tell that the device is gone if a command is issued to it.  I had hoped that
> I could detect hot-pull/scsi-remove-single-device operations via this
> callback.
> Granted, for some drivers, recreating and destroying state associated with a
> particular device might be pretty cheap, but certainly not in all cases.
> The
> aic7xxx and aic79xx drivers maintain domain validation and other negotiation
> state in these structures.  You certainly don't want to go through another
> full
> Domain Validation sequence the next time a device is allocated via
> slave_alloc() if the device isn't really "new".
> 
> Any chance in changing this behavior?

Justin,
Yes, that behaviour does seem inconsistent with the
description of slave_alloc() and slave_destroy().

This post from 29th November shows a trace from a
device scan being done on the scsi_debug driver:
marc.theaimsgroup.com/?l=linux-scsi&m=103855771307230&w=2

I believe Pat Mansfield has done most of the recent
work in th device scan area and he is currently on
holiday.

Doug Gilbert