submitted as: https://github.com/ceph-dovecot/dovecot-ceph-plugin/pull/272

commit cbccc030421472d2455bf0c584ea1490bf03dd16
Author: root <root@test2.local>
Date:   Mon Aug 24 13:28:24 2020 +0000

    some compiling fixes

diff --git a/src/storage-rbox/ostream-bufferlist.cpp b/src/storage-rbox/ostream-bufferlist.cpp
index 83f4880..2c3f0b6 100644
--- a/src/storage-rbox/ostream-bufferlist.cpp
+++ b/src/storage-rbox/ostream-bufferlist.cpp
@@ -63,7 +63,7 @@ static ssize_t o_stream_buffer_sendv(struct ostream_private *stream, const struc
   }
   for (i = 0; i < iov_count; i++) {
     // use unsigned char* for binary data!
-    bstream->buf->append(reinterpret_cast<const unsigned char *>(iov[i].iov_base), iov[i].iov_len);
+    bstream->buf->append(reinterpret_cast<const char *>(iov[i].iov_base), iov[i].iov_len);
     stream->ostream.offset += iov[i].iov_len;
     ret += iov[i].iov_len;
   }