md/raid10: print more useful messages on device failure.

When we get a read error on a device in a RAID10, and attempting to
repair the error fails, print more useful messages about why it
failed.

Signed-off-by: Robert Becker <Rob.Becker@riverbed.com>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/raid10.c

@@ -1488,6 +1488,7 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
 		/* write it back and re-read */
 		rcu_read_lock();
 		while (sl != r10_bio->read_slot) {
+			char b[BDEVNAME_SIZE];
 			int d;
 			if (sl==0)
 				sl = conf->copies;
@@ -1503,9 +1504,21 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
 						 r10_bio->devs[sl].addr +
 						 sect + rdev->data_offset,
 						 s<<9, conf->tmppage, WRITE)
-				    == 0)
+				    == 0) {
 					/* Well, this device is dead */
+					printk(KERN_NOTICE
+					       "raid10:%s: read correction "
+					       "write failed"
+					       " (%d sectors at %llu on %s)\n",
+					       mdname(mddev), s,
+					       (unsigned long long)(sect+
+					       rdev->data_offset),
+					       bdevname(rdev->bdev, b));
+					printk(KERN_NOTICE "raid10:%s: failing "
+					       "drive\n",
+					       bdevname(rdev->bdev, b));
 					md_error(mddev, rdev);
+				}
 				rdev_dec_pending(rdev, mddev);
 				rcu_read_lock();
 			}
@@ -1526,10 +1539,22 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
 				if (sync_page_io(rdev->bdev,
 						 r10_bio->devs[sl].addr +
 						 sect + rdev->data_offset,
-						 s<<9, conf->tmppage, READ) == 0)
+						 s<<9, conf->tmppage,
+						 READ) == 0) {
 					/* Well, this device is dead */
+					printk(KERN_NOTICE
+					       "raid10:%s: unable to read back "
+					       "corrected sectors"
+					       " (%d sectors at %llu on %s)\n",
+					       mdname(mddev), s,
+					       (unsigned long long)(sect+
+						    rdev->data_offset),
+					       bdevname(rdev->bdev, b));
+					printk(KERN_NOTICE "raid10:%s: failing drive\n",
+					       bdevname(rdev->bdev, b));
+
 					md_error(mddev, rdev);
-				else
+				} else {
 					printk(KERN_INFO
 					       "raid10:%s: read error corrected"
 					       " (%d sectors at %llu on %s)\n",
@@ -1537,6 +1562,7 @@ static void fix_read_error(conf_t *conf, mddev_t *mddev, r10bio_t *r10_bio)
 					       (unsigned long long)(sect+
 					            rdev->data_offset),
 					       bdevname(rdev->bdev, b));
+				}
 
 				rdev_dec_pending(rdev, mddev);
 				rcu_read_lock();