scsi: target: transport should handle st FM/EOM/ILI reads

When a tape drive is exported via LIO using the pscsi module, a read
that requests more bytes per block than the tape can supply returns an
empty buffer. This is because the pscsi pass-through target module sees
the "ILI" illegal length bit set and thinks there is no reason to return
the data.

This is a long-standing transport issue, since it assumes that no data
need be returned under a check condition, which isn't always the case
for tape.

Add in a check for tape reads with the ILI, EOM, or FM bits set, with a
sense code of NO_SENSE, treating such cases as if the read
succeeded. The layered tape driver then "does the right thing" when it
gets such a response.

Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 24 insertions, 2 deletions

diff --git a/drivers/target/target_core_pscsi.c b/drivers/target/target_core_pscsi.c
index 0d99b242e82e..f31215b1d009 100644
--- a/drivers/target/target_core_pscsi.c
+++ b/drivers/target/target_core_pscsi.c
@@ -689,8 +689,29 @@ after_mode_sense:
 	}
 after_mode_select:
 
-	if (scsi_status == SAM_STAT_CHECK_CONDITION)
+	if (scsi_status == SAM_STAT_CHECK_CONDITION) {
 		transport_copy_sense_to_cmd(cmd, req_sense);
+
+		/*
+		 * check for TAPE device reads with
+		 * FM/EOM/ILI set, so that we can get data
+		 * back despite framework assumption that a
+		 * check condition means there is no data
+		 */
+		if (sd->type == TYPE_TAPE &&
+		    cmd->data_direction == DMA_FROM_DEVICE) {
+			/*
+			 * is sense data valid, fixed format,
+			 * and have FM, EOM, or ILI set?
+			 */
+			if (req_sense[0] == 0xf0 &&	/* valid, fixed format */
+			    req_sense[2] & 0xe0 &&	/* FM, EOM, or ILI */
+			    (req_sense[2] & 0xf) == 0) { /* key==NO_SENSE */
+				pr_debug("Tape FM/EOM/ILI status detected. Treat as normal read.\n");
+				cmd->se_cmd_flags |= SCF_TREAT_READ_AS_NORMAL;
+			}
+		}
+	}
 }
 
 enum {
@@ -1061,7 +1082,8 @@ static void pscsi_req_done(struct request *req, blk_status_t status)
 
 	switch (host_byte(result)) {
 	case DID_OK:
-		target_complete_cmd(cmd, scsi_status);
+		target_complete_cmd_with_length(cmd, scsi_status,
+			cmd->data_length - scsi_req(req)->resid_len);
 		break;
 	default:
 		pr_debug("PSCSI Host Byte exception at cmd: %p CDB:"