Add support for reading BDB without the library

This commit implements a slow read-only backend that allows
accessing of BerkeleyDB databases without using the BerkeleyDB
library. The code supports btree version 9 and hash version 8
and 9.

There are two use cases for this:

1) Conversion of an existing BerkeleyDB to a different
   backend.

2) Allowing package scriptlets to do database queries while
   in a transaction that replaced rpm with a version that
   no longer links against BerkeleyDB.

Currently prefix searching is not supported (but it would be
easy to add).

configure.ac

@@ -594,6 +594,20 @@ AS_IF([test "$enable_ndb" = yes],[
 ])
 AM_CONDITIONAL([NDB], [test "$enable_ndb" = yes])
 
+#=================
+# Process --enable-bdb-ro
+AC_ARG_ENABLE([bdb-ro], [AS_HELP_STRING([--enable-bdb-ro (EXPERIMENTAL)],[enable the read-only Berkeley DB code])],
+[case "$enable_bdb_ro" in
+yes|no) ;;
+*) AC_MSG_ERROR([invalid argument to --enable-bdb-ro])
+  ;;
+esac],
+[enable_bdb_ro=no])
+AS_IF([test "$enable_bdb_ro" = yes],[
+  AC_DEFINE(WITH_BDB_RO, 1, [Build with read-only Berkeley DB])
+])
+AM_CONDITIONAL([BDB_RO], [test "$enable_bdb_ro" = yes])
+
 #=================
 # Check for LMDB support
 AC_ARG_ENABLE([lmdb],

lib/Makefile.am

@@ -68,6 +68,10 @@ librpm_la_LIBADD += @WITH_DB_LIB@
 endif
 endif
 
+if BDB_RO
+librpm_la_SOURCES += backend/bdb_ro.c
+endif
+
 if NDB
 librpm_la_SOURCES += \
 	backend/ndb/glue.c \