btrfs: extend balance filter limit to take minimum and maximum
The 'limit' filter is underdesigned, it should have been a range for
[min,max], with some relaxed semantics when one of the bounds is
missing. Besides that, using a full u64 for a single value is a waste of
bytes.
Let's fix both by extending the use of the u64 bytes for the [min,max]
range. This can be done in a backward compatible way, the range will be
interpreted only if the appropriate flag is set
(BTRFS_BALANCE_ARGS_LIMIT_RANGE).
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 3fa3c3b..460cd69 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -846,8 +846,18 @@
/* BTRFS_BALANCE_ARGS_* */
__le64 flags;
- /* BTRFS_BALANCE_ARGS_LIMIT value */
- __le64 limit;
+ /*
+ * BTRFS_BALANCE_ARGS_LIMIT with value 'limit'
+ * BTRFS_BALANCE_ARGS_LIMIT_RANGE - the extend version can use minimum
+ * and maximum
+ */
+ union {
+ __le64 limit;
+ struct {
+ __le32 limit_min;
+ __le32 limit_max;
+ };
+ };
__le64 unused[7];
} __attribute__ ((__packed__));