Fix the `tape drive spinning indefinately upon mt stat' problem.

With the recent changes in the CAM error handling, some problems in
the error handling of sa(4) have been uncovered.  Basically, a number
of conditions that are not actually errors have been mistreated as
genuine errors.  In particular:

. Trying to read in variable length mode with a mismatched blocksize
  between the on-tape (virtual) blocks and the read(2) supplied buffer
  size, causing an ILI SCSI condition, have caused an attempt to retry
  the supposedly `errored' transfer, causing the tape to be read
  continuously until it eventually hit EOM.  Since by default any
  simple mt(1) operation does an initial test read, an `mt stat' was
  sufficient to trigger this bug.

  Note that it's Justin's opinion that treating a NO SENSE as an EIO
  is another bug in CAM.  I feel not authorized to fix cam_periph.c
  without another confirmation that i'm on the right track, however.

. Hitting a filemark caused the read(2) syscall to return EIO, instead
  of returning a `short read'.  Note that the current fix only solves
  this problem in variable length mode.  Fixed length mode uses a
  different code path, and since i didn't grok all the intentions behind
  that handling, i did not touch it (IOW: it's still broken, and you get
  an EIO upon hitting a filemark).

The solution is to keep track of those conditions inside saerror(),
and upon completion to not call cam_periph_error() in that case.  We
need to make sure that the device gets unfrozen if needed though (in
case of actual errors, cam_periph_error() does this on our behalf).

Not objected by:       mjacob (who currently doesn't have the time to
			      review the patch)

1 files changed, 15 insertions, 2 deletions

diff --git a/sys/cam/scsi/scsi_sa.c b/sys/cam/scsi/scsi_sa.c
index adfbbb0..318534e 100644
--- a/sys/cam/scsi/scsi_sa.c
+++ b/sys/cam/scsi/scsi_sa.c
@@ -2286,7 +2286,7 @@ saerror(union ccb *ccb, u_int32_t cflgs, u_int32_t sflgs)
 	u_int32_t resid = 0;
 	int32_t	info = 0;
 	int	error_code, sense_key, asc, ascq;
-	int	error, defer_action;
+	int	error, defer_action, no_actual_error = FALSE;
 
 	periph = xpt_path_periph(ccb->ccb_h.path);
 	softc = (struct sa_softc *)periph->softc;
@@ -2396,6 +2396,8 @@ saerror(union ccb *ccb, u_int32_t cflgs, u_int32_t sflgs)
 			if (defer_action) {
 				error = -1;
 				softc->flags |= SA_FLAG_EOF_PENDING;
+			} else {
+				no_actual_error = TRUE;
 			}
 			/*
 			 * Unconditionally, if we detected a filemark on a read,
@@ -2424,6 +2426,8 @@ saerror(union ccb *ccb, u_int32_t cflgs, u_int32_t sflgs)
 					softc->flags |= SA_FLAG_EIO_PENDING;
 				else
 					error = EIO;
+			} else {
+				no_actual_error = TRUE;
 			}
 			/*
 			 * Bump the block number if we hadn't seen a filemark.
@@ -2438,8 +2442,17 @@ saerror(union ccb *ccb, u_int32_t cflgs, u_int32_t sflgs)
 			}
 		}
 	}
-	if (error == 0)
+	if (error == 0 && !no_actual_error)
 		return (cam_periph_error(ccb, cflgs, sflgs, &softc->saved_ccb));
+	if (no_actual_error) {
+		if ((ccb->ccb_h.status & CAM_DEV_QFRZN) != 0) 
+			cam_release_devq(ccb->ccb_h.path,
+					 /* relsim_flags */0,
+					 /* openings */0,
+					 /* timeout */0,
+					 /* getcount_only */ FALSE);
+		return (0);
+	}
 
 	if (error == -1)
 		return (0);