ocfs2: Define data structures for discontiguous block groups.

Defines the OCFS2_FEATURE_INCOMPAT_DISCONTIG_BG feature bit and modifies
struct ocfs2_group_desc for the feature.

Signed-off-by: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Tao Ma <tao.ma@oracle.com>

1 files changed, 46 insertions, 7 deletions

diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index d61a1521b10e..448aa8d11a97 100644
--- a/fs/ocfs2/ocfs2_fs.h
+++ b/fs/ocfs2/ocfs2_fs.h
@@ -165,6 +165,9 @@
 /* Refcount tree support */
 #define OCFS2_FEATURE_INCOMPAT_REFCOUNT_TREE    0x1000
 
+/* Discontigous block groups */
+#define OCFS2_FEATURE_INCOMPAT_DISCONTIG_BG     0x2000
+
 /*
  * backup superblock flag is used to indicate that this volume
  * has backup superblocks.
@@ -832,6 +835,13 @@ struct ocfs2_dx_leaf {
 };
 
 /*
+ * Largest bitmap for a block (suballocator) group in bytes.  This limit
+ * does not affect cluster groups (global allocator).  Cluster group
+ * bitmaps run to the end of the block.
+ */
+#define OCFS2_MAX_BG_BITMAP_SIZE        256
+
+/*
  * On disk allocator group structure for OCFS2
  */
 struct ocfs2_group_desc
@@ -852,7 +862,29 @@ struct ocfs2_group_desc
         __le64   bg_blkno;               /* Offset on disk, in blocks */
 /*30*/  struct ocfs2_block_check bg_check;      /* Error checking */
         __le64   bg_reserved2;
-/*40*/  __u8    bg_bitmap[0];
+/*40*/  union {
+                __u8    bg_bitmap[0];
+                struct {
+                        /*
+                         * Block groups may be discontiguous when
+                         * OCFS2_FEATURE_INCOMPAT_DISCONTIG_BG is set.
+                         * The extents of a discontigous block group are
+                         * stored in bg_list.  It is a flat list.
+                         * l_tree_depth must always be zero.  A
+                         * discontiguous group is signified by a non-zero
+                         * bg_list->l_next_free_rec.  Only block groups
+                         * can be discontiguous; Cluster groups cannot.
+                         * We've never made a block group with more than
+                         * 2048 blocks (256 bytes of bg_bitmap).  This
+                         * codifies that limit so that we can fit bg_list.
+                         * bg_size of a discontiguous block group will
+                         * be 256 to match bg_bitmap_filler.
+                         */
+                        __u8 bg_bitmap_filler[OCFS2_MAX_BG_BITMAP_SIZE];
+/*140*/                 struct ocfs2_extent_list bg_list;
+                };
+        };
+/* Actual on-disk size is one block */
 };
 
 struct ocfs2_refcount_rec {
@@ -1276,12 +1308,16 @@ static inline u16 ocfs2_local_alloc_size(struct super_block *sb)
         return size;
 }
 
-static inline int ocfs2_group_bitmap_size(struct super_block *sb)
+static inline int ocfs2_group_bitmap_size(struct super_block *sb,
+                                          int suballocator)
 {
         int size;
 
-        size = sb->s_blocksize -
-                offsetof(struct ocfs2_group_desc, bg_bitmap);
+        if (suballocator)
+                size = OCFS2_MAX_BG_BITMAP_SIZE;
+        else
+                size = sb->s_blocksize -
+                        offsetof(struct ocfs2_group_desc, bg_bitmap);
 
         return size;
 }
@@ -1404,12 +1440,15 @@ static inline int ocfs2_local_alloc_size(int blocksize)
         return size;
 }
 
-static inline int ocfs2_group_bitmap_size(int blocksize)
+static inline int ocfs2_group_bitmap_size(int blocksize, int suballocator)
 {
         int size;
 
-        size = blocksize -
-                offsetof(struct ocfs2_group_desc, bg_bitmap);
+        if (suballocator)
+                size = OCFS2_MAX_BG_BITMAP_SIZE;
+        else
+                size = blocksize -
+                        offsetof(struct ocfs2_group_desc, bg_bitmap);
 
         return size;
 }