[PATCH] md: teach raid5 the difference between 'check' and 'repair'.

With this, raid5 can be asked to check parity without repairing it.  It also
keeps a count of the number of incorrect parity blocks found (mismatches) and
reports them through sysfs.

Signed-off-by: Neil Brown <neilb@suse.de>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 25 insertions, 2 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 37400873b879..e58d61d9f31b 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1758,16 +1758,29 @@ md_store_scan(mddev_t *mddev, const char *page, size_t len)
         return len;
 }
 
+static ssize_t
+md_show_mismatch(mddev_t *mddev, char *page)
+{
+        return sprintf(page, "%llu\n",
+                       (unsigned long long) mddev->resync_mismatches);
+}
+
 static struct md_sysfs_entry md_scan_mode = {
         .attr = {.name = "scan_mode", .mode = S_IRUGO|S_IWUSR },
         .show = md_show_scan,
         .store = md_store_scan,
 };
 
+static struct md_sysfs_entry md_mismatches = {
+        .attr = {.name = "mismatch_cnt", .mode = S_IRUGO },
+        .show = md_show_mismatch,
+};
+
 static struct attribute *md_default_attrs[] = {
         &md_level.attr,
         &md_raid_disks.attr,
         &md_scan_mode.attr,
+        &md_mismatches.attr,
         NULL,
 };
 
@@ -3888,12 +3901,13 @@ static void md_do_sync(mddev_t *mddev)
                 }
         } while (mddev->curr_resync < 2);
 
-        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
+        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                 /* resync follows the size requested by the personality,
                  * which defaults to physical size, but can be virtual size
                  */
                 max_sectors = mddev->resync_max_sectors;
-        else
+                mddev->resync_mismatches = 0;
+        } else
                 /* recovery follows the physical size of devices */
                 max_sectors = mddev->size << 1;
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 121fbaa9ed59..ce154553aca5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -1292,6 +1292,11 @@ static void handle_stripe(struct stripe_head *sh)
                             !memcmp(pagea, pagea+4, STRIPE_SIZE-4)) {
                                 /* parity is correct (on disc, not in buffer any more) */
                                 set_bit(STRIPE_INSYNC, &sh->state);
+                        } else {
+                                conf->mddev->resync_mismatches += STRIPE_SECTORS;
+                                if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
+                                        /* don't try to repair!! */
+                                        set_bit(STRIPE_INSYNC, &sh->state);
                         }
                 }
                 if (!test_bit(STRIPE_INSYNC, &sh->state)) {
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index efd04dca0abd..cb8b44d1588b 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -175,6 +175,10 @@ struct mddev_s
         sector_t                        resync_mark_cnt;/* blocks written at resync_mark */
 
         sector_t                        resync_max_sectors; /* may be set by personality */
+
+        sector_t                        resync_mismatches; /* count of sectors where
+                                                            * parity/replica mismatch found
+                                                            */
         /* recovery/resync flags 
          * NEEDED:   we might need to start a resync/recover
          * RUNNING:  a thread is running, or about to be started