[PATCH] md: allow md array component size to be accessed and 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, 98 insertions, 42 deletions

diff --git a/Documentation/md.txt b/Documentation/md.txt
index 9710138d101a..0a2e10a4040d 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -174,6 +174,15 @@ All md devices contain:
      The size should be atleast PAGE_SIZE (4k) and should be a power
      of 2.  This can only be set while assembling an array
 
+  component_size
+     For arrays with data redundancy (i.e. not raid0, linear, faulty,
+     multipath), all components must be the same size - or at least
+     there must a size that they all provide space for.  This is a key
+     part or the geometry of the array.  It is measured in sectors
+     and can be read from here.  Writing to this value may resize
+     the array if the personality supports it (raid1, raid5, raid6),
+     and if the component drives are large enough.
+
 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 9e57e97bd530..d568ab4a487f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1820,6 +1820,44 @@ __ATTR(chunk_size, 0644, chunk_size_show, chunk_size_store);
 
 
 static ssize_t
+size_show(mddev_t *mddev, char *page)
+{
+        return sprintf(page, "%llu\n", (unsigned long long)mddev->size);
+}
+
+static int update_size(mddev_t *mddev, unsigned long size);
+
+static ssize_t
+size_store(mddev_t *mddev, const char *buf, size_t len)
+{
+        /* If array is inactive, we can reduce the component size, but
+         * not increase it (except from 0).
+         * If array is active, we can try an on-line resize
+         */
+        char *e;
+        int err = 0;
+        unsigned long long size = simple_strtoull(buf, &e, 10);
+        if (!*buf || *buf == '\n' ||
+            (*e && *e != '\n'))
+                return -EINVAL;
+
+        if (mddev->pers) {
+                err = update_size(mddev, size);
+                md_update_sb(mddev);
+        } else {
+                if (mddev->size == 0 ||
+                    mddev->size > size)
+                        mddev->size = size;
+                else
+                        err = -ENOSPC;
+        }
+        return err ? err : len;
+}
+
+static struct md_sysfs_entry md_size =
+__ATTR(component_size, 0644, size_show, size_store);
+
+static ssize_t
 action_show(mddev_t *mddev, char *page)
 {
         char *type = "idle";
@@ -1887,6 +1925,7 @@ static struct attribute *md_default_attrs[] = {
         &md_level.attr,
         &md_raid_disks.attr,
         &md_chunk_size.attr,
+        &md_size.attr,
         NULL,
 };
 
@@ -3005,6 +3044,54 @@ static int set_array_info(mddev_t * mddev, mdu_array_info_t *info)
         return 0;
 }
 
+static int update_size(mddev_t *mddev, unsigned long size)
+{
+        mdk_rdev_t * rdev;
+        int rv;
+        struct list_head *tmp;
+
+        if (mddev->pers->resize == NULL)
+                return -EINVAL;
+        /* The "size" is the amount of each device that is used.
+         * This can only make sense for arrays with redundancy.
+         * linear and raid0 always use whatever space is available
+         * We can only consider changing the size if no resync
+         * or reconstruction is happening, and if the new size
+         * is acceptable. It must fit before the sb_offset or,
+         * if that is <data_offset, it must fit before the
+         * size of each device.
+         * If size is zero, we find the largest size that fits.
+         */
+        if (mddev->sync_thread)
+                return -EBUSY;
+        ITERATE_RDEV(mddev,rdev,tmp) {
+                sector_t avail;
+                int fit = (size == 0);
+                if (rdev->sb_offset > rdev->data_offset)
+                        avail = (rdev->sb_offset*2) - rdev->data_offset;
+                else
+                        avail = get_capacity(rdev->bdev->bd_disk)
+                                - rdev->data_offset;
+                if (fit && (size == 0 || size > avail/2))
+                        size = avail/2;
+                if (avail < ((sector_t)size << 1))
+                        return -ENOSPC;
+        }
+        rv = mddev->pers->resize(mddev, (sector_t)size *2);
+        if (!rv) {
+                struct block_device *bdev;
+
+                bdev = bdget_disk(mddev->gendisk, 0);
+                if (bdev) {
+                        down(&bdev->bd_inode->i_sem);
+                        i_size_write(bdev->bd_inode, mddev->array_size << 10);
+                        up(&bdev->bd_inode->i_sem);
+                        bdput(bdev);
+                }
+        }
+        return rv;
+}
+
 /*
  * update_array_info is used to change the configuration of an
  * on-line array.
@@ -3053,49 +3140,9 @@ static int update_array_info(mddev_t *mddev, mdu_array_info_t *info)
                 else
                         return mddev->pers->reconfig(mddev, info->layout, -1);
         }
-        if (mddev->size != info->size) {
-                mdk_rdev_t * rdev;
-                struct list_head *tmp;
-                if (mddev->pers->resize == NULL)
-                        return -EINVAL;
-                /* The "size" is the amount of each device that is used.
-                 * This can only make sense for arrays with redundancy.
-                 * linear and raid0 always use whatever space is available
-                 * We can only consider changing the size if no resync
-                 * or reconstruction is happening, and if the new size
-                 * is acceptable. It must fit before the sb_offset or,
-                 * if that is <data_offset, it must fit before the
-                 * size of each device.
-                 * If size is zero, we find the largest size that fits.
-                 */
-                if (mddev->sync_thread)
-                        return -EBUSY;
-                ITERATE_RDEV(mddev,rdev,tmp) {
-                        sector_t avail;
-                        int fit = (info->size == 0);
-                        if (rdev->sb_offset > rdev->data_offset)
-                                avail = (rdev->sb_offset*2) - rdev->data_offset;
-                        else
-                                avail = get_capacity(rdev->bdev->bd_disk)
-                                        - rdev->data_offset;
-                        if (fit && (info->size == 0 || info->size > avail/2))
-                                info->size = avail/2;
-                        if (avail < ((sector_t)info->size << 1))
-                                return -ENOSPC;
-                }
-                rv = mddev->pers->resize(mddev, (sector_t)info->size *2);
-                if (!rv) {
-                        struct block_device *bdev;
+        if (mddev->size != info->size)
+                rv = update_size(mddev, info->size);
 
-                        bdev = bdget_disk(mddev->gendisk, 0);
-                        if (bdev) {
-                                down(&bdev->bd_inode->i_sem);
-                                i_size_write(bdev->bd_inode, mddev->array_size << 10);
-                                up(&bdev->bd_inode->i_sem);
-                                bdput(bdev);
-                        }
-                }
-        }
         if (mddev->raid_disks    != info->raid_disks) {
                 /* change the number of raid disks */
                 if (mddev->pers->reshape == NULL)