2 files changed, 32 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 80f158745ca5..f3d418ba625e 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -205,6 +205,12 @@ All md devices contain:
      simply a number that is interpretted differently by different
      levels.  It can be written while assembling an array.
 
+  resync_start
+     The point at which resync should start.  If no resync is needed,
+     this will be a very large number.  At array creation it will
+     default to 0, though starting the array as 'clean' will
+     set it much larger.
+
    new_dev
      This file can be written but not read.  The value written should
      be a block device number as major:minor.  e.g. 8:0
diff --git a/drivers/md/md.c b/drivers/md/md.c
index e3261c438a65..8603c0692eab 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2235,6 +2235,30 @@ chunk_size_store(mddev_t *mddev, const char *buf, size_t len)
 static struct md_sysfs_entry md_chunk_size =
 __ATTR(chunk_size, 0644, chunk_size_show, chunk_size_store);
 
+static ssize_t
+resync_start_show(mddev_t *mddev, char *page)
+{
+        return sprintf(page, "%llu\n", (unsigned long long)mddev->recovery_cp);
+}
+
+static ssize_t
+resync_start_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        /* can only set chunk_size if array is not yet active */
+        char *e;
+        unsigned long long n = simple_strtoull(buf, &e, 10);
+
+        if (mddev->pers)
+                return -EBUSY;
+        if (!*buf || (*e && *e != '\n'))
+                return -EINVAL;
+
+        mddev->recovery_cp = n;
+        return len;
+}
+static struct md_sysfs_entry md_resync_start =
+__ATTR(resync_start, 0644, resync_start_show, resync_start_store);
+
 /*
  * The array state can be:
  *
@@ -2771,6 +2795,7 @@ static struct attribute *md_default_attrs[] = {
         &md_raid_disks.attr,
         &md_chunk_size.attr,
         &md_size.attr,
+        &md_resync_start.attr,
         &md_metadata.attr,
         &md_new_device.attr,
         &md_safe_delay.attr,
@@ -3263,6 +3288,7 @@ static int do_md_stop(mddev_t * mddev, int mode)
                 mddev->array_size = 0;
                 mddev->size = 0;
                 mddev->raid_disks = 0;
+                mddev->recovery_cp = 0;
 
                 disk = mddev->gendisk;
                 if (disk)