Add endio error handler.
--- diff/drivers/md/dm-hw-handler.c	2004-10-29 15:37:46.000000000 +0100
+++ source/drivers/md/dm-hw-handler.c	2004-10-29 15:38:04.000000000 +0100
@@ -27,7 +27,7 @@
 {
 	struct hwh_internal *hwhi;
 
-	list_for_each_entry (hwhi, &_hw_handlers, list) {
+	list_for_each_entry(hwhi, &_hw_handlers, list) {
 		if (!strcmp(name, hwhi->hwht.name))
 			return hwhi;
 	}
@@ -86,7 +86,7 @@
 	if (hwhi->use < 0)
 		BUG();
 
-out:
+      out:
 	up_read(&_hwh_lock);
 }
 
@@ -149,5 +149,68 @@
 	return 0;
 }
 
+unsigned dm_hw_handler_err(struct hw_handler *hwh, struct bio *bio)
+{
+	int sense_key, asc, ascq;
+
+#if 0
+	if (bio->bi_error & BIO_SENSE) {
+		/* FIXME: This is just an initial guess. */
+		/* key / asc / ascq */
+		sense_key = (bio->bi_error >> 16) & 0xff;
+		asc = (bio->bi_error >> 8) & 0xff;
+		ascq = bio->bi_error & 0xff;
+
+		switch (sense_key) {
+			/* This block as a whole comes from the device.
+			 * So no point retrying on another path. */
+		case 0x03:	/* Medium error */
+		case 0x05:	/* Illegal request */
+		case 0x07:	/* Data protect */
+		case 0x08:	/* Blank check */
+		case 0x0a:	/* copy aborted */
+		case 0x0c:	/* obsolete - no clue ;-) */
+		case 0x0d:	/* volume overflow */
+		case 0x0e:	/* data miscompare */
+		case 0x0f:	/* reserved - no idea either. */
+			return 0;
+
+			/* For these errors it's unclear whether they
+			 * come from the device or the controller.
+			 * So just lets try a different path, and if
+			 * it eventually succeeds, user-space will clear
+			 * the paths again... */
+		case 0x02:	/* Not ready */
+		case 0x04:	/* Hardware error */
+		case 0x09:	/* vendor specific */
+		case 0x0b:	/* Aborted command */
+			return MP_FAIL_PATH | MP_RETRY_IO;
+
+		case 0x06:	/* Unit attention - might want to decode */
+			if (asc == 0x04 && ascq == 0x01)
+				/* "Unit in the process of
+				 * becoming ready" */
+				return MP_RETRY_IO;
+			return MP_FAIL_PATH | MP_RETRY_IO;
+
+			/* FIXME: For Unit Not Ready we may want
+			 * to have a generic pg activation
+			 * feature (START_UNIT). */
+
+			/* Should these two ever end up in the
+			 * error path? I don't think so. */
+		case 0x00:	/* No sense */
+		case 0x01:	/* Recovered error */
+			return MP_RETRY_IO;
+		}
+	}
+#endif
+
+	/* We got no idea how to decode the other kinds of errors ->
+	 * assume generic error condition. */
+	return MP_FAIL_PATH | MP_RETRY_IO;
+}
+
 EXPORT_SYMBOL(dm_register_hw_handler);
 EXPORT_SYMBOL(dm_unregister_hw_handler);
+EXPORT_SYMBOL(dm_hw_handler_err);
--- diff/drivers/md/dm-hw-handler.h	2004-10-29 15:37:46.000000000 +0100
+++ source/drivers/md/dm-hw-handler.h	2004-10-29 15:38:04.000000000 +0100
@@ -23,6 +23,7 @@
 typedef int (*hwh_ctr_fn) (struct hw_handler *hwh, unsigned arc, char **argv);
 typedef void (*hwh_dtr_fn) (struct hw_handler *hwh);
 
+typedef unsigned (*hwh_err_fn) (struct hw_handler *hwh, struct bio *bio);
 typedef	int (*hwh_status_fn) (struct hw_handler *hwh,
 			      status_type_t type,
 			      char *result, unsigned int maxlen);
@@ -35,6 +36,7 @@
 	hwh_ctr_fn ctr;
 	hwh_dtr_fn dtr;
 
+	hwh_err_fn err;
 	hwh_status_fn status;
 };
 
@@ -50,4 +52,12 @@
 /* Releases a hardware handler  */
 void dm_put_hw_handler(struct hw_handler_type *hwht);
 
+/* Default hwh_err_fn */
+unsigned dm_hw_handler_err(struct hw_handler *hwh, struct bio *bio);
+
+/* hwh_err_fn return flags */
+#define MP_FAIL_PATH 1
+#define MP_BYPASS_PG 2
+#define MP_RETRY_IO  4
+
 #endif
--- diff/drivers/md/dm-mpath.c	2004-10-29 15:37:58.000000000 +0100
+++ source/drivers/md/dm-mpath.c	2004-10-29 15:38:04.000000000 +0100
@@ -634,15 +634,25 @@
 	return r;
 }
 
+static void bypass_pg(struct multipath *m, struct priority_group *pg,
+		      int bypass)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&m->lock, flags);
+	pg->bypass = bypass;
+	m->current_path = NULL;
+	spin_unlock_irqrestore(&m->lock, flags);
+}
+
 /*
  * Set/clear bypass status of a PG.
  * PG numbering goes 1, 2, 3...
  */
-static int bypass_pg(struct multipath *m, const char *pgstr, int bypass)
+static int bypass_pg_num(struct multipath *m, const char *pgstr, int bypass)
 {
 	struct priority_group *pg;
 	unsigned pgnum;
-	unsigned long flags;
 
 	if (!pgstr || (sscanf(pgstr, "%u", &pgnum) != 1) || !pgnum)
 		goto error;
@@ -651,10 +661,7 @@
 		if (--pgnum)
 			continue;
 
-		spin_lock_irqsave(&m->lock, flags);
-		pg->bypass = bypass;
-		m->current_path = NULL;
-		spin_unlock_irqrestore(&m->lock, flags);
+		bypass_pg(m, pg, bypass);
 
 		return 0;
 	}
@@ -668,6 +675,8 @@
 		     int error, struct mpath_io *mpio)
 {
 	int r;
+	struct hw_handler *hwh = &m->hw_handler;
+	unsigned err_flags = MP_FAIL_PATH;	/* Default behavior */
 
 	if (error) {
 		spin_lock(&m->lock);
@@ -677,7 +686,17 @@
 		}
 		spin_unlock(&m->lock);
 
-		fail_path(mpio->path);
+		if (hwh && hwh->type->err)
+			err_flags = hwh->type->err(hwh, bio);
+
+		if (err_flags & MP_FAIL_PATH)
+			fail_path(mpio->path);
+		
+		if (err_flags & MP_BYPASS_PG)
+			bypass_pg(m, mpio->path->pg, 1);
+
+		if (!(err_flags & MP_RETRY_IO))
+			return -EIO;
 
 		/* remap */
 		dm_bio_restore(&mpio->details, bio);
@@ -781,9 +800,9 @@
 		goto error;
 
 	if (!strnicmp(argv[0], "disable_group", 14))
-		return bypass_pg(m, argv[1], 0);
+		return bypass_pg_num(m, argv[1], 0);
 	else if (!strnicmp(argv[0], "enable_group", 13))
-		return bypass_pg(m, argv[1], 1);
+		return bypass_pg_num(m, argv[1], 1);
 	else if (!strnicmp(argv[0], "reinstate", 10))
 		action = reinstate_path;
 	else if (!strnicmp(argv[0], "fail", 5))