xfs: create a standard btree size calculator code

Create a helper to generate AG btree height calculator functions.
This will be used (much) later when we get to the refcount btree.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index 7be8d9c..50cfb98 100644 (file)
--- a/fs/xfs/libxfs/xfs_btree.c
+++ b/fs/xfs/libxfs/xfs_btree.c
@@ -4797,3 +4797,27 @@ xfs_btree_query_range(
        return xfs_btree_overlapped_query_range(cur, &low_key, &high_key,
                        fn, priv);
 }
+
+/*
+ * Calculate the number of blocks needed to store a given number of records
+ * in a short-format (per-AG metadata) btree.
+ */
+xfs_extlen_t
+xfs_btree_calc_size(
+       struct xfs_mount        *mp,
+       uint                    *limits,
+       unsigned long long      len)
+{
+       int                     level;
+       int                     maxrecs;
+       xfs_extlen_t            rval;
+
+       maxrecs = limits[0];
+       for (level = 0, rval = 0; len > 1; level++) {
+               len += maxrecs - 1;
+               do_div(len, maxrecs);
+               maxrecs = limits[1];
+               rval += len;
+       }
+       return rval;
+}

diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h
index f41a4cf..1c148f5 100644 (file)
--- a/fs/xfs/libxfs/xfs_btree.h
+++ b/fs/xfs/libxfs/xfs_btree.h
@@ -501,6 +501,8 @@ bool xfs_btree_sblock_v5hdr_verify(struct xfs_buf *bp);
 bool xfs_btree_sblock_verify(struct xfs_buf *bp, unsigned int max_recs);
 uint xfs_btree_compute_maxlevels(struct xfs_mount *mp, uint *limits,
                                 unsigned long len);
+xfs_extlen_t xfs_btree_calc_size(struct xfs_mount *mp, uint *limits,
+               unsigned long long len);
 
 /* return codes */
 #define XFS_BTREE_QUERY_RANGE_CONTINUE 0       /* keep iterating */