+/**
+ * calc_reserved - Calculate the number of blocks to reserve when
+ * refunding a transaction's unused buffers.
+ * @sdp: The GFS2 superblock
+ *
+ * This is complex. We need to reserve room for all our currently used
+ * metadata buffers (e.g. normal file I/O rewriting file time stamps) and
+ * all our journaled data buffers for journaled files (e.g. files in the
+ * meta_fs like rindex, or files for which chattr +j was done.)
+ * If we don't reserve enough space, gfs2_log_refund and gfs2_log_flush
+ * will count it as free space (sd_log_blks_free) and corruption will follow.
+ *
+ * We can have metadata bufs and jdata bufs in the same journal. So each
+ * type gets its own log header, for which we need to reserve a block.
+ * In fact, each type has the potential for needing more than one header
+ * in cases where we have more buffers than will fit on a journal page.
+ * Metadata journal entries take up half the space of journaled buffer entries.
+ * Thus, metadata entries have buf_limit (502) and journaled buffers have
+ * databuf_limit (251) before they cause a wrap around.
+ *
+ * Also, we need to reserve blocks for revoke journal entries and one for an
+ * overall header for the lot.
+ *
+ * Returns: the number of blocks reserved
+ */
+static unsigned int calc_reserved(struct gfs2_sbd *sdp)
+{
+ unsigned int reserved = 0;
+ unsigned int mbuf_limit, metabufhdrs_needed;
+ unsigned int dbuf_limit, databufhdrs_needed;
+ unsigned int revokes = 0;
+
+ mbuf_limit = buf_limit(sdp);
+ metabufhdrs_needed = (sdp->sd_log_commited_buf +
+ (mbuf_limit - 1)) / mbuf_limit;
+ dbuf_limit = databuf_limit(sdp);
+ databufhdrs_needed = (sdp->sd_log_commited_databuf +
+ (dbuf_limit - 1)) / dbuf_limit;
+
+ if (sdp->sd_log_commited_revoke)
+ revokes = gfs2_struct2blk(sdp, sdp->sd_log_commited_revoke,
+ sizeof(u64));
+
+ reserved = sdp->sd_log_commited_buf + metabufhdrs_needed +
+ sdp->sd_log_commited_databuf + databufhdrs_needed +
+ revokes;
+ /* One for the overall header */
+ if (reserved)
+ reserved++;
+ return reserved;
+}
+