md: 'array_size' sysfs attribute

Allow userspace to set the size of the array according to the following
semantics:

1/ size must be <= to the size returned by mddev->pers->size(mddev, 0, 0)
   a) If size is set before the array is running, do_md_run will fail
      if size is greater than the default size
   b) A reshape attempt that reduces the default size to less than the set
      array size should be blocked
2/ once userspace sets the size the kernel will not change it
3/ writing 'default' to this attribute returns control of the size to the
   kernel and reverts to the size reported by the personality

Also, convert locations that need to know the default size from directly
reading ->array_sectors to <pers>_size.  Resync/reshape operations
always follow the default size.

Finally, fixup other locations that read a number of 1k-blocks from
userspace to use strict_blocks_to_sectors() which checks for unsigned
long long to sector_t overflow and blocks to sectors overflow.

Reviewed-by: Andre Noll <maan@systemlinux.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 044116b53f7a..b4f4badc0068 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2125,14 +2125,16 @@ static int raid1_resize(mddev_t *mddev, sector_t sectors)
          * worth it.
          */
         md_set_array_sectors(mddev, raid1_size(mddev, sectors, 0));
+        if (mddev->array_sectors > raid1_size(mddev, sectors, 0))
+                return -EINVAL;
         set_capacity(mddev->gendisk, mddev->array_sectors);
         mddev->changed = 1;
-        if (mddev->array_sectors > mddev->dev_sectors &&
+        if (sectors > mddev->dev_sectors &&
             mddev->recovery_cp == MaxSector) {
                 mddev->recovery_cp = mddev->dev_sectors;
                 set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
         }
-        mddev->dev_sectors = mddev->array_sectors;
+        mddev->dev_sectors = sectors;
         mddev->resync_max_sectors = sectors;
         return 0;
 }