Re: st(4) and mt eom

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

On Mar 21,  6:48am, Frank Kardel wrote:
} 
} As I wrote, extending MTIO ioctls to support more mt commands is not a 
} real issue (e. g. add access to the LOCATE command). We just need to 
} decide which features are useful to support and find the time to 
} implement them.

     Yes, those would be enhancements, not bug fixes.  Also, what
software would use these enhancements besides mt(1).  Some of the
stuff, like informational items and control items, look to be useful
in their own right, but other stuff, like locate, look to be
redundant.

} For Bacula it wouldn't help right now, thus the EOM code needs fixing.

     For this, it is debatable if it is an enhancement or a bug
fix.  However, it is needed by a significant application, which
should raise its priority.

} There are also some other things that are useful to add to the SCSI 
} subsystem like acquiring timeout information from the device to avoid 
} early device resets while the drive is still fighting with its servo 
} errors (just happened to me with a bad LTO7 drive). I have that update 
} currently sitting in my tree.

     Getting timeout information from the device would be useful.
I had a problem with an earlier tape changer.  If I issued a tape
move command without first rewinding the tape, the operation would
often timeout.  This would cause a SCSI bus reset to be issued
while the tape was rewinding.  Then it would try to probe the
changer while it was still resetting.  This drove the changer crazy.
At first, I tried to remember to rewind the tape before issuing a
move command.  Eventually I found the right spot in our code and
changed the timeout.

} On 03/21/19 04:27, John Nemeth wrote:
} > On Mar 20,  8:08pm, Frank Kardel wrote:
} > }
} > } This seems to be a long standing deficiency of the driver. Looking at
} > } the SCSI spec it is recommended to issue a READ POSITION command
} >
} >       I did read a book about SCSI sometime ago, so I have a good
} > overview of CCBs and the protocol, but it has been some time since
} > I've looked at it in any depth.  And, although I've made minor
} > changes to our SCSI code, I can't say that I know it in any depth.
} >
} > }
} [snip]
}-- End of excerpt from Frank Kardel