return cur->bc_mp->m_rtrmap_mxr[level != 0];
 }
 
+/* Calculate number of records in the ondisk realtime rmap btree inode root. */
+unsigned int
+xfs_rtrmapbt_droot_maxrecs(
+       unsigned int            blocklen,
+       bool                    leaf)
+{
+       blocklen -= sizeof(struct xfs_rtrmap_root);
+
+       if (leaf)
+               return blocklen / sizeof(struct xfs_rmap_rec);
+       return blocklen / (2 * sizeof(struct xfs_rmap_key) +
+                       sizeof(xfs_rtrmap_ptr_t));
+}
+
+/*
+ * Get the maximum records we could store in the on-disk format.
+ *
+ * For non-root nodes this is equivalent to xfs_rtrmapbt_get_maxrecs, but
+ * for the root node this checks the available space in the dinode fork
+ * so that we can resize the in-memory buffer to match it.  After a
+ * resize to the maximum size this function returns the same value
+ * as xfs_rtrmapbt_get_maxrecs for the root node, too.
+ */
+STATIC int
+xfs_rtrmapbt_get_dmaxrecs(
+       struct xfs_btree_cur    *cur,
+       int                     level)
+{
+       if (level != cur->bc_nlevels - 1)
+               return cur->bc_mp->m_rtrmap_mxr[level != 0];
+       return xfs_rtrmapbt_droot_maxrecs(cur->bc_ino.forksize, level == 0);
+}
+
 /*
  * Convert the ondisk record's offset field into the ondisk key's offset field.
  * Fork and bmbt are significant parts of the rmap record key, but written
                                 be32_to_cpu(key2->rmap.rm_startblock));
 }
 
+static inline void
+xfs_rtrmapbt_move_ptrs(
+       struct xfs_mount        *mp,
+       struct xfs_btree_block  *broot,
+       short                   old_size,
+       size_t                  new_size,
+       unsigned int            numrecs)
+{
+       void                    *dptr;
+       void                    *sptr;
+
+       sptr = xfs_rtrmap_broot_ptr_addr(mp, broot, 1, old_size);
+       dptr = xfs_rtrmap_broot_ptr_addr(mp, broot, 1, new_size);
+       memmove(dptr, sptr, numrecs * sizeof(xfs_rtrmap_ptr_t));
+}
+
+static struct xfs_btree_block *
+xfs_rtrmapbt_broot_realloc(
+       struct xfs_btree_cur    *cur,
+       unsigned int            new_numrecs)
+{
+       struct xfs_mount        *mp = cur->bc_mp;
+       struct xfs_ifork        *ifp = xfs_btree_ifork_ptr(cur);
+       struct xfs_btree_block  *broot;
+       unsigned int            new_size;
+       unsigned int            old_size = ifp->if_broot_bytes;
+       const unsigned int      level = cur->bc_nlevels - 1;
+
+       new_size = xfs_rtrmap_broot_space_calc(mp, level, new_numrecs);
+
+       /* Handle the nop case quietly. */
+       if (new_size == old_size)
+               return ifp->if_broot;
+
+       if (new_size > old_size) {
+               unsigned int    old_numrecs;
+
+               /*
+                * If there wasn't any memory allocated before, just allocate
+                * it now and get out.
+                */
+               if (old_size == 0)
+                       return xfs_broot_realloc(ifp, new_size);
+
+               /*
+                * If there is already an existing if_broot, then we need to
+                * realloc it and possibly move the node block pointers because
+                * those are not butted up against the btree block header.
+                */
+               old_numrecs = xfs_rtrmapbt_maxrecs(mp, old_size, level == 0);
+               broot = xfs_broot_realloc(ifp, new_size);
+               if (level > 0)
+                       xfs_rtrmapbt_move_ptrs(mp, broot, old_size, new_size,
+                                       old_numrecs);
+               goto out_broot;
+       }
+
+       /*
+        * We're reducing numrecs.  If we're going all the way to zero, just
+        * free the block.
+        */
+       ASSERT(ifp->if_broot != NULL && old_size > 0);
+       if (new_size == 0) {
+               xfs_broot_free(ifp);
+               return NULL;
+       }
+
+       /*
+        * Shrink the btree root by possibly moving the rtrmapbt pointers,
+        * since they are not butted up against the btree block header.  Then
+        * reallocate broot.
+        */
+       if (level > 0)
+               xfs_rtrmapbt_move_ptrs(mp, ifp->if_broot, old_size, new_size,
+                               new_numrecs);
+       broot = xfs_broot_realloc(ifp, new_size);
+
+out_broot:
+       ASSERT(xfs_rtrmap_droot_space(broot) <=
+              xfs_inode_fork_size(cur->bc_ino.ip, cur->bc_ino.whichfork));
+       return broot;
+}
+
 const struct xfs_btree_ops xfs_rtrmapbt_ops = {
        .name                   = "rtrmap",
        .type                   = XFS_BTREE_TYPE_INODE,
        .free_block             = xfs_btree_free_metafile_block,
        .get_minrecs            = xfs_rtrmapbt_get_minrecs,
        .get_maxrecs            = xfs_rtrmapbt_get_maxrecs,
+       .get_dmaxrecs           = xfs_rtrmapbt_get_dmaxrecs,
        .init_key_from_rec      = xfs_rtrmapbt_init_key_from_rec,
        .init_high_key_from_rec = xfs_rtrmapbt_init_high_key_from_rec,
        .init_rec_from_cur      = xfs_rtrmapbt_init_rec_from_cur,
        .keys_inorder           = xfs_rtrmapbt_keys_inorder,
        .recs_inorder           = xfs_rtrmapbt_recs_inorder,
        .keys_contiguous        = xfs_rtrmapbt_keys_contiguous,
+       .broot_realloc          = xfs_rtrmapbt_broot_realloc,
 };
 
 /* Allocate a new rt rmap btree cursor. */
        return max_t(xfs_filblks_t, mp->m_rgblocks >> 6,
                        xfs_rtrmapbt_max_size(mp, mp->m_rgblocks));
 }
+
+/* Convert on-disk form of btree root to in-memory form. */
+STATIC void
+xfs_rtrmapbt_from_disk(
+       struct xfs_inode        *ip,
+       struct xfs_rtrmap_root  *dblock,
+       unsigned int            dblocklen,
+       struct xfs_btree_block  *rblock)
+{
+       struct xfs_mount        *mp = ip->i_mount;
+       struct xfs_rmap_key     *fkp;
+       __be64                  *fpp;
+       struct xfs_rmap_key     *tkp;
+       __be64                  *tpp;
+       struct xfs_rmap_rec     *frp;
+       struct xfs_rmap_rec     *trp;
+       unsigned int            rblocklen = xfs_rtrmap_broot_space(mp, dblock);
+       unsigned int            numrecs;
+       unsigned int            maxrecs;
+
+       xfs_btree_init_block(mp, rblock, &xfs_rtrmapbt_ops, 0, 0, ip->i_ino);
+
+       rblock->bb_level = dblock->bb_level;
+       rblock->bb_numrecs = dblock->bb_numrecs;
+       numrecs = be16_to_cpu(dblock->bb_numrecs);
+
+       if (be16_to_cpu(rblock->bb_level) > 0) {
+               maxrecs = xfs_rtrmapbt_droot_maxrecs(dblocklen, false);
+               fkp = xfs_rtrmap_droot_key_addr(dblock, 1);
+               tkp = xfs_rtrmap_key_addr(rblock, 1);
+               fpp = xfs_rtrmap_droot_ptr_addr(dblock, 1, maxrecs);
+               tpp = xfs_rtrmap_broot_ptr_addr(mp, rblock, 1, rblocklen);
+               memcpy(tkp, fkp, 2 * sizeof(*fkp) * numrecs);
+               memcpy(tpp, fpp, sizeof(*fpp) * numrecs);
+       } else {
+               frp = xfs_rtrmap_droot_rec_addr(dblock, 1);
+               trp = xfs_rtrmap_rec_addr(rblock, 1);
+               memcpy(trp, frp, sizeof(*frp) * numrecs);
+       }
+}
+
+/* Load a realtime reverse mapping btree root in from disk. */
+int
+xfs_iformat_rtrmap(
+       struct xfs_inode        *ip,
+       struct xfs_dinode       *dip)
+{
+       struct xfs_mount        *mp = ip->i_mount;
+       struct xfs_rtrmap_root  *dfp = XFS_DFORK_PTR(dip, XFS_DATA_FORK);
+       struct xfs_btree_block  *broot;
+       unsigned int            numrecs;
+       unsigned int            level;
+       int                     dsize;
+
+       dsize = XFS_DFORK_SIZE(dip, mp, XFS_DATA_FORK);
+       numrecs = be16_to_cpu(dfp->bb_numrecs);
+       level = be16_to_cpu(dfp->bb_level);
+
+       if (level > mp->m_rtrmap_maxlevels ||
+           xfs_rtrmap_droot_space_calc(level, numrecs) > dsize)
+               return -EFSCORRUPTED;
+
+       broot = xfs_broot_realloc(xfs_ifork_ptr(ip, XFS_DATA_FORK),
+                       xfs_rtrmap_broot_space_calc(mp, level, numrecs));
+       if (broot)
+               xfs_rtrmapbt_from_disk(ip, dfp, dsize, broot);
+       return 0;
+}
+
+/* Convert in-memory form of btree root to on-disk form. */
+void
+xfs_rtrmapbt_to_disk(
+       struct xfs_mount        *mp,
+       struct xfs_btree_block  *rblock,
+       unsigned int            rblocklen,
+       struct xfs_rtrmap_root  *dblock,
+       unsigned int            dblocklen)
+{
+       struct xfs_rmap_key     *fkp;
+       __be64                  *fpp;
+       struct xfs_rmap_key     *tkp;
+       __be64                  *tpp;
+       struct xfs_rmap_rec     *frp;
+       struct xfs_rmap_rec     *trp;
+       unsigned int            numrecs;
+       unsigned int            maxrecs;
+
+       ASSERT(rblock->bb_magic == cpu_to_be32(XFS_RTRMAP_CRC_MAGIC));
+       ASSERT(uuid_equal(&rblock->bb_u.l.bb_uuid, &mp->m_sb.sb_meta_uuid));
+       ASSERT(rblock->bb_u.l.bb_blkno == cpu_to_be64(XFS_BUF_DADDR_NULL));
+       ASSERT(rblock->bb_u.l.bb_leftsib == cpu_to_be64(NULLFSBLOCK));
+       ASSERT(rblock->bb_u.l.bb_rightsib == cpu_to_be64(NULLFSBLOCK));
+
+       dblock->bb_level = rblock->bb_level;
+       dblock->bb_numrecs = rblock->bb_numrecs;
+       numrecs = be16_to_cpu(rblock->bb_numrecs);
+
+       if (be16_to_cpu(rblock->bb_level) > 0) {
+               maxrecs = xfs_rtrmapbt_droot_maxrecs(dblocklen, false);
+               fkp = xfs_rtrmap_key_addr(rblock, 1);
+               tkp = xfs_rtrmap_droot_key_addr(dblock, 1);
+               fpp = xfs_rtrmap_broot_ptr_addr(mp, rblock, 1, rblocklen);
+               tpp = xfs_rtrmap_droot_ptr_addr(dblock, 1, maxrecs);
+               memcpy(tkp, fkp, 2 * sizeof(*fkp) * numrecs);
+               memcpy(tpp, fpp, sizeof(*fpp) * numrecs);
+       } else {
+               frp = xfs_rtrmap_rec_addr(rblock, 1);
+               trp = xfs_rtrmap_droot_rec_addr(dblock, 1);
+               memcpy(trp, frp, sizeof(*frp) * numrecs);
+       }
+}
+
+/* Flush a realtime reverse mapping btree root out to disk. */
+void
+xfs_iflush_rtrmap(
+       struct xfs_inode        *ip,
+       struct xfs_dinode       *dip)
+{
+       struct xfs_ifork        *ifp = xfs_ifork_ptr(ip, XFS_DATA_FORK);
+       struct xfs_rtrmap_root  *dfp = XFS_DFORK_PTR(dip, XFS_DATA_FORK);
+
+       ASSERT(ifp->if_broot != NULL);
+       ASSERT(ifp->if_broot_bytes > 0);
+       ASSERT(xfs_rtrmap_droot_space(ifp->if_broot) <=
+                       xfs_inode_fork_size(ip, XFS_DATA_FORK));
+       xfs_rtrmapbt_to_disk(ip->i_mount, ifp->if_broot, ifp->if_broot_bytes,
+                       dfp, XFS_DFORK_SIZE(dip, ip->i_mount, XFS_DATA_FORK));
+}
 
 unsigned int xfs_rtrmapbt_maxrecs(struct xfs_mount *mp, unsigned int blocklen,
                bool leaf);
 void xfs_rtrmapbt_compute_maxlevels(struct xfs_mount *mp);
+unsigned int xfs_rtrmapbt_droot_maxrecs(unsigned int blocklen, bool leaf);
 
 /*
  * Addresses of records, keys, and pointers within an incore rtrmapbt block.
 
 xfs_filblks_t xfs_rtrmapbt_calc_reserves(struct xfs_mount *mp);
 
+/* Addresses of key, pointers, and records within an ondisk rtrmapbt block. */
+
+static inline struct xfs_rmap_rec *
+xfs_rtrmap_droot_rec_addr(
+       struct xfs_rtrmap_root  *block,
+       unsigned int            index)
+{
+       return (struct xfs_rmap_rec *)
+               ((char *)(block + 1) +
+                (index - 1) * sizeof(struct xfs_rmap_rec));
+}
+
+static inline struct xfs_rmap_key *
+xfs_rtrmap_droot_key_addr(
+       struct xfs_rtrmap_root  *block,
+       unsigned int            index)
+{
+       return (struct xfs_rmap_key *)
+               ((char *)(block + 1) +
+                (index - 1) * 2 * sizeof(struct xfs_rmap_key));
+}
+
+static inline xfs_rtrmap_ptr_t *
+xfs_rtrmap_droot_ptr_addr(
+       struct xfs_rtrmap_root  *block,
+       unsigned int            index,
+       unsigned int            maxrecs)
+{
+       return (xfs_rtrmap_ptr_t *)
+               ((char *)(block + 1) +
+                maxrecs * 2 * sizeof(struct xfs_rmap_key) +
+                (index - 1) * sizeof(xfs_rtrmap_ptr_t));
+}
+
+/*
+ * Address of pointers within the incore btree root.
+ *
+ * These are to be used when we know the size of the block and
+ * we don't have a cursor.
+ */
+static inline xfs_rtrmap_ptr_t *
+xfs_rtrmap_broot_ptr_addr(
+       struct xfs_mount        *mp,
+       struct xfs_btree_block  *bb,
+       unsigned int            index,
+       unsigned int            block_size)
+{
+       return xfs_rtrmap_ptr_addr(bb, index,
+                       xfs_rtrmapbt_maxrecs(mp, block_size, false));
+}
+
+/*
+ * Compute the space required for the incore btree root containing the given
+ * number of records.
+ */
+static inline size_t
+xfs_rtrmap_broot_space_calc(
+       struct xfs_mount        *mp,
+       unsigned int            level,
+       unsigned int            nrecs)
+{
+       size_t                  sz = XFS_RTRMAP_BLOCK_LEN;
+
+       if (level > 0)
+               return sz + nrecs * (2 * sizeof(struct xfs_rmap_key) +
+                                        sizeof(xfs_rtrmap_ptr_t));
+       return sz + nrecs * sizeof(struct xfs_rmap_rec);
+}
+
+/*
+ * Compute the space required for the incore btree root given the ondisk
+ * btree root block.
+ */
+static inline size_t
+xfs_rtrmap_broot_space(struct xfs_mount *mp, struct xfs_rtrmap_root *bb)
+{
+       return xfs_rtrmap_broot_space_calc(mp, be16_to_cpu(bb->bb_level),
+                       be16_to_cpu(bb->bb_numrecs));
+}
+
+/* Compute the space required for the ondisk root block. */
+static inline size_t
+xfs_rtrmap_droot_space_calc(
+       unsigned int            level,
+       unsigned int            nrecs)
+{
+       size_t                  sz = sizeof(struct xfs_rtrmap_root);
+
+       if (level > 0)
+               return sz + nrecs * (2 * sizeof(struct xfs_rmap_key) +
+                                        sizeof(xfs_rtrmap_ptr_t));
+       return sz + nrecs * sizeof(struct xfs_rmap_rec);
+}
+
+/*
+ * Compute the space required for the ondisk root block given an incore root
+ * block.
+ */
+static inline size_t
+xfs_rtrmap_droot_space(struct xfs_btree_block *bb)
+{
+       return xfs_rtrmap_droot_space_calc(be16_to_cpu(bb->bb_level),
+                       be16_to_cpu(bb->bb_numrecs));
+}
+
+int xfs_iformat_rtrmap(struct xfs_inode *ip, struct xfs_dinode *dip);
+void xfs_rtrmapbt_to_disk(struct xfs_mount *mp, struct xfs_btree_block *rblock,
+               unsigned int rblocklen, struct xfs_rtrmap_root *dblock,
+               unsigned int dblocklen);
+void xfs_iflush_rtrmap(struct xfs_inode *ip, struct xfs_dinode *dip);
+
 #endif /* __XFS_RTRMAP_BTREE_H__ */