[PATCH] md: allow available size of component devices to be set via sysfs

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

2 files changed, 32 insertions, 0 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 866a1a887547..7b3d471bb9f0 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -250,6 +250,13 @@ Each directory contains:
         the device before this offset us not touched, unless it is
         used for storing metadata (Formats 1.1 and 1.2).
 
+      size
+        The amount of the device, after the offset, that can be used
+        for storage of data.  This will normally be the same as the
+        component_size.  This can be written while assembling an
+        array.  If a value less than the current component_size is
+        written, component_size will be reduced to this value.
+
 
 An active md device will also contain and entry for each active device
 in the array.  These are named
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 27db100d8b12..40ac7fbab61f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1686,12 +1686,37 @@ offset_store(mdk_rdev_t *rdev, const char *buf, size_t len)
 static struct rdev_sysfs_entry rdev_offset =
 __ATTR(offset, 0644, offset_show, offset_store);
 
+static ssize_t
+rdev_size_show(mdk_rdev_t *rdev, char *page)
+{
+        return sprintf(page, "%llu\n", (unsigned long long)rdev->size);
+}
+
+static ssize_t
+rdev_size_store(mdk_rdev_t *rdev, const char *buf, size_t len)
+{
+        char *e;
+        unsigned long long size = simple_strtoull(buf, &e, 10);
+        if (e==buf || (*e && *e != '\n'))
+                return -EINVAL;
+        if (rdev->mddev->pers)
+                return -EBUSY;
+        rdev->size = size;
+        if (size < rdev->mddev->size || rdev->mddev->size == 0)
+                rdev->mddev->size = size;
+        return len;
+}
+
+static struct rdev_sysfs_entry rdev_size =
+__ATTR(size, 0644, rdev_size_show, rdev_size_store);
+
 static struct attribute *rdev_default_attrs[] = {
         &rdev_state.attr,
         &rdev_super.attr,
         &rdev_errors.attr,
         &rdev_slot.attr,
         &rdev_offset.attr,
+        &rdev_size.attr,
         NULL,
 };
 static ssize_t