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[dm-devel] [patch 3/3] Add retries to hp hardware handler if path initialization command completes with a check condition.



This patch adds retries to the hp hardware handler, and utilizes the 
MP_RETRY flag of dm-multipath.  For now in the hp handler, if we get a 
pg_init completed with a check condition we just assume we can retry the
pg_init command.  We make this assumption because of incomplete data on
specific check condition code of the HP hardware, and because testing
has shown the HP path initialization command to be idempotent.
The number of times we retry is settable via the "pg_init_retries"
multipath map feature.

Signed-off-by: Dave Wysochanski <dwysocha redhat com>
Acked-by: Chandra Seetharaman <sekharan us ibm com>

---
Index: linux-2.6.23-rc1/drivers/md/dm-mpath-hp-sw.c
===================================================================
--- linux-2.6.23-rc1.orig/drivers/md/dm-mpath-hp-sw.c
+++ linux-2.6.23-rc1/drivers/md/dm-mpath-hp-sw.c
@@ -18,18 +18,52 @@
 #include <linux/types.h>
 #include <scsi/scsi.h>
 #include <scsi/scsi_cmnd.h>
+#include <scsi/scsi_dbg.h>
 
 #include "dm.h"
 #include "dm-hw-handler.h"
 
 #define DM_MSG_PREFIX "multipath hp_sw"
 #define HP_DM_HWH_NAME "hp_sw"
-#define HP_DM_HWH_VER "0.0.3"
+#define HP_DM_HWH_VER "1.0.0"
 
 struct hp_sw_context {
 	unsigned char sense[SCSI_SENSE_BUFFERSIZE];
 };
 
+/**
+ * hp_sw_error_is_retryable - Is an HP-specific check condition retryable?
+ * @req: path activation request
+ *
+ * Examine error codes of request and determine whether the error is retryable.
+ * Some error codes are already retried by scsi-ml (see
+ * scsi_decide_disposition), but some HP specific codes are not.
+ * The intent of this routine is to supply the logic for the HP specific
+ * check conditions.
+ *
+ * Returns:
+ *  1 - command completed with retryable error
+ *  0 - command completed with non-retryable error
+ *
+ * Possible optimizations
+ * 1. More hardware-specific error codes
+ */
+static int hp_sw_error_is_retryable(struct request *req)
+{
+	/*
+	 * NOT_READY is known to be retryable
+	 * For now we just dump out the sense data and call it retryable
+	 */
+	if (status_byte(req->errors) == CHECK_CONDITION)
+		__scsi_print_sense("hp_sw", req->sense, req->sense_len);
+
+	/*
+	 * At this point we don't have complete information about all the error
+	 * codes from this hardware, so we are just conservative and retry
+	 * when in doubt.
+	 */
+	return 1;
+}
 
 /**
  * hp_sw_end_io - Completion handler for HP path activation.
@@ -41,8 +75,6 @@ struct hp_sw_context {
  *
  * Context: scsi-ml softirq
  *
- * Possible optimizations
- * 1. Actually check sense data for retryable error (e.g. NOT_READY)
  */
 static void hp_sw_end_io(struct request *req, int error)
 {
@@ -54,11 +86,17 @@ static void hp_sw_end_io(struct request 
 		DMDEBUG("%s path activation command - success",
 			path->dev->name);
 	} else {
-		DMWARN("%s path activation command - error=0x%x",
+		if (hp_sw_error_is_retryable(req)) {
+			DMDEBUG("%s path activation command - retry",
+				path->dev->name);
+			err_flags = MP_RETRY;
+			goto out;
+		}
+		DMWARN("%s path activation fail - error=0x%x",
 		       path->dev->name, error);
 		err_flags = MP_FAIL_PATH;
 	}
-
+out:
 	req->end_io_data = NULL;
 	__blk_put_request(req->q, req);
 	dm_pg_init_complete(path, err_flags);
@@ -136,7 +174,7 @@ static void hp_sw_pg_init(struct hw_hand
 	if (!req) {
 		DMERR("%s path activation command - allocation fail",
 		      path->dev->name);
-		goto fail;
+		goto retry;
 	}
 
 	DMDEBUG("%s path activation command - sent", path->dev->name);
@@ -144,8 +182,8 @@ static void hp_sw_pg_init(struct hw_hand
 	blk_execute_rq_nowait(req->q, NULL, req, 1, hp_sw_end_io);
 	return;
 
-fail:
-	dm_pg_init_complete(path, MP_FAIL_PATH);
+retry:
+	dm_pg_init_complete(path, MP_RETRY);
 }
 
 static int hp_sw_create(struct hw_handler *hwh, unsigned argc, char **argv)

-- 


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