[PATCH 2/2] scsi: st: Record the tape position after a successful MTLOAD

[Laurence Oberman <loberman@redhat.com>]

Commit 0b120edb37dc ("scsi: st: Add MTIOCGET and MTLOAD to ioctls allowed
after device reset") allows MTLOAD to clear the reset condition because
the tape location is known after MTLOAD.  But the driver does not record
it: reset_state() sets the file and block numbers to -1, and
do_load_unload() leaves them there.  check_tape() sets them to 0 only for
a new session, which requires a new-medium unit attention.  Drives that
do not report one when the medium was already loaded (seen with IBM LTO
drives) keep reporting file/block -1 in MTIOCGET and no BOT, although the
tape is at the beginning.

Set the file and block numbers to 0 after a successful load when the
current partition is 0, where LOAD positions the medium.

Fixes: 0b120edb37dc ("scsi: st: Add MTIOCGET and MTLOAD to ioctls allowed after device reset")
Assisted-by: Claude sashiko
Signed-off-by: Laurence Oberman <loberman@redhat.com>
---
 drivers/scsi/st.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 0a4263bef9cb..8889714122c7 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -2686,6 +2686,14 @@ static int do_load_unload(struct scsi_tape *STp, struct file *filp, int load_cod
 		else {
 			STp->rew_at_close = STp->autorew_dev;
 			retval = check_tape(STp, filp);
+			/*
+			 * LOAD leaves the medium at the beginning of partition
+			 * 0.  check_tape() records that only for a new session;
+			 * without a new-medium unit attention (the medium was
+			 * already loaded) the position would stay unknown.
+			 */
+			if (retval == CHKRES_READY && STp->partition == 0)
+				STp->ps[0].drv_file = STp->ps[0].drv_block = 0;
 			if (retval > 0)
 				retval = 0;
 		}
-- 
2.55.0