> On 15. Nov 2024, at 19.45, Kai Mäkisara (Kolumbus) <kai.makisara@xxxxxxxxxxx> wrote: > ... > > I still think that UNIT ATTENTIONs (UAs) reach the high level device without > problems. The problem is that the device attached to the target first issuing > a SCSI command after reset gets the UA. As long as this is st device, > there are no problems. But, if it is the sg device attached to the same target, > the tape device misses it. > ... > > And there are cases where the device reset does not originate from the > same computer. > > Does anyone have any suggestions? Besides Power on/Reset, the same problem applies to the New Media case. One solution might be the following: the midlevel maintains counters for the Power on/Reset and the Media change UNIT ATTENTIONs. The ULDs can read these counters (using wrappers). If the ULD find for a device that the counter value has changed, then the event corresponding to the counter has occurred. The problem of clearing event flags is avoided, A drawback comes from the counter wrap-arounds. If, e.g., four-bit counters are used and there are 16 Power on/Resets between the checks by the ULD, the event is missed when the counter is used. (The ULDs should also check the sense data they do receive. It is possible/probable that the event is recognized based on the sense data even if the counter check misses it.) This solution is easy to implement. I have a test implementation running and it seems to be working. Other solutions that have come into my mind are much more complicated than the counters. Here are examples: - the UNIT ATTENTIONs would be sent to all ULDs attached to the device when they issue the next SCSI command - the ULDs would have possibility to register a callback for UNIT ATTENTIONs
