[0/3] scsi: st: improve pos_unknown handling after reset

Message

John Meneghini Oct. 31, 2024, 1 a.m. UTC

These patches address some issues with positoin lost handling which
where introduced by commit 9604eea5bd3a ("scsi: st: Add third party
poweron reset handling"). That commit added code which detected any
unexpected power on/reset unit attention to st_chk_results() and
correclty set pos_unknown in the driver.

However, the aforementioned changes is catching POR UAs that are
expected as well as those that are unexpected as st_chk_results() sets
pos_unknown every time a POR UA is seen.  This results in a change of
behavior that is confusing as some tape drives can set a POR UA when the
system reboots, the driver reloads, or a tape is reloaded. This results
in regressions as MTIOGET now fails following and kind of reset.

These issues are documented in the kernel bugzilla:

Link: https://bugzilla.kernel.org/show_bug.cgi?id=219419

A reproducer test script can be found at: 

Link: https://github.com/johnmeneghini/tape_tests

John Meneghini (3):
  scsi: st: instrument the pos_unknown code
  scsi: st: clear was_reset when CHKRES_NEW_SESSION
  scsi: st: clear pos_unknown when the por ua is expected

 drivers/scsi/st.c | 63 ++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 54 insertions(+), 9 deletions(-)