2 files changed, 68 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 7b3d471bb9f0..b8d172b254f7 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -200,6 +200,14 @@ All md devices contain:
      This can be written only while the array is being assembled, not
      after it is started.
 
+   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
+     This will cause that device to be attached to the array, if it is
+     available.  It will then appear at md/dev-XXX (depending on the
+     name of the device) and further configuration is then possible.
+
+
 As component devices are added to an md array, they appear in the 'md'
 directory as new directories named
       dev-XXX
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 40ac7fbab61f..825e235b791b 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1987,6 +1987,65 @@ 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
+null_show(mddev_t *mddev, char *page)
+{
+        return -EINVAL;
+}
+
+static ssize_t
+new_dev_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        /* buf must be %d:%d\n? giving major and minor numbers */
+        /* The new device is added to the array.
+         * If the array has a persistent superblock, we read the
+         * superblock to initialise info and check validity.
+         * Otherwise, only checking done is that in bind_rdev_to_array,
+         * which mainly checks size.
+         */
+        char *e;
+        int major = simple_strtoul(buf, &e, 10);
+        int minor;
+        dev_t dev;
+        mdk_rdev_t *rdev;
+        int err;
+
+        if (!*buf || *e != ':' || !e[1] || e[1] == '\n')
+                return -EINVAL;
+        minor = simple_strtoul(e+1, &e, 10);
+        if (*e && *e != '\n')
+                return -EINVAL;
+        dev = MKDEV(major, minor);
+        if (major != MAJOR(dev) ||
+            minor != MINOR(dev))
+                return -EOVERFLOW;
+
+
+        if (mddev->persistent) {
+                rdev = md_import_device(dev, mddev->major_version,
+                                        mddev->minor_version);
+                if (!IS_ERR(rdev) && !list_empty(&mddev->disks)) {
+                        mdk_rdev_t *rdev0 = list_entry(mddev->disks.next,
+                                                       mdk_rdev_t, same_set);
+                        err = super_types[mddev->major_version]
+                                .load_super(rdev, rdev0, mddev->minor_version);
+                        if (err < 0)
+                                goto out;
+                }
+        } else
+                rdev = md_import_device(dev, -1, -1);
+
+        if (IS_ERR(rdev))
+                return PTR_ERR(rdev);
+        err = bind_rdev_to_array(rdev, mddev);
+ out:
+        if (err)
+                export_rdev(rdev);
+        return err ? err : len;
+}
+
+static struct md_sysfs_entry md_new_device =
+__ATTR(new_dev, 0200, null_show, new_dev_store);
 
 static ssize_t
 size_show(mddev_t *mddev, char *page)
@@ -2144,6 +2203,7 @@ static struct attribute *md_default_attrs[] = {
         &md_chunk_size.attr,
         &md_size.attr,
         &md_metadata.attr,
+        &md_new_device.attr,
         NULL,
 };