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diff --git a/contrib/bind9/doc/misc/sdb b/contrib/bind9/doc/misc/sdb new file mode 100644 index 0000000..0de0ab8 --- /dev/null +++ b/contrib/bind9/doc/misc/sdb @@ -0,0 +1,169 @@ +Copyright (C) 2004 Internet Systems Consortium, Inc. ("ISC") +Copyright (C) 2000, 2001 Internet Software Consortium. +See COPYRIGHT in the source root or http://isc.org/copyright.html for terms. + +Using the BIND 9 Simplified Database Interface + +This document describes the care and feeding of the BIND 9 Simplified +Database Interface, which allows you to extend BIND 9 with new ways +of obtaining the data that is published as DNS zones. + + +The Original BIND 9 Database Interface + +BIND 9 has a well-defined "back-end database interface" that makes it +possible to replace the component of the name server responsible for +the storage and retrieval of zone data, called the "database", on a +per-zone basis. The default database is an in-memory, red-black-tree +data structure commonly referred to as "rbtdb", but it is possible to +write drivers to support any number of alternative database +technologies such as in-memory hash tables, application specific +persistent on-disk databases, object databases, or relational +databases. + +The original BIND 9 database interface defined in <dns/db.h> is +designed to efficiently support the full set of database functionality +needed by a name server that implements the complete DNS protocols, +including features such as zone transfers, dynamic update, and DNSSEC. +Each of these aspects of name server operations places its own set of +demands on the data store, with the result that the database API is +quite complex and contains operations that are highly specific to the +DNS. For example, data are stored in a binary format, the name space +is tree structured, and sets of data records are conceptually +associated with DNSSEC signature sets. For these reasons, writing a +driver using this interface is a highly nontrivial undertaking. + + +The Simplified Database Interface + +Many BIND users wish to provide access to various data sources through +the DNS, but are not necessarily interested in completely replacing +the in-memory "rbt" database or in supporting features like dynamic +update, DNSSEC, or even zone transfers. + +Often, all you want is limited, read-only DNS access to an existing +system. For example, you may have an existing relational database +containing hostname/address mappings and wish to provide forvard and +reverse DNS lookups based on this information. Or perhaps you want to +set up a simple DNS-based load balancing system where the name server +answers queries about a single DNS name with a dynamically changing +set of A records. + +BIND 9.1 introduced a new, simplified database interface, or "sdb", +which greatly simplifies the writing of drivers for these kinds of +applications. + + +The sdb Driver + +An sdb driver is an object module, typically written in C, which is +linked into the name server and registers itself with the sdb +subsystem. It provides a set of callback functions, which also serve +to advertise its capabilities. When the name server receives DNS +queries, invokes the callback functions to obtain the data to respond +with. + +Unlike the full database interface, the sdb interface represents all +domain names and resource records as ASCII text. + + +Writing an sdb Driver + +When a driver is registered, it specifies its name, a list of callback +functions, and flags. + +The flags specify whether the driver wants to use relative domain +names where possible. + +The callback functions are as follows. The only one that must be +defined is lookup(). + + - create(zone, argc, argv, driverdata, dbdata) + Create a database object for "zone". + + - destroy(zone, driverdata, dbdata) + Destroy the database object for "zone". + + - lookup(zone, name, dbdata, lookup) + Return all the records at the domain name "name". + + - authority(zone, dbdata, lookup) + Return the SOA and NS records at the zone apex. + + - allnodes(zone, dbdata, allnodes) + Return all data in the zone, for zone transfers. + +For more detail about these functions and their parameters, see +bind9/lib/dns/include/dns/sdb.h. For example drivers, see +bind9/contrib/sdb. + + +Rebuilding the Server + +The driver module and header file must be copied to (or linked into) +the bind9/bin/named and bind9/bin/named/include directories +respectively, and must be added to the DBDRIVER_OBJS and DBDRIVER_SRCS +lines in bin/named/Makefile.in (e.g. for the timedb sample sdb driver, +add timedb.c to DBDRIVER_SRCS and timedb.@O@ to DBDRIVER_OBJS). If +the driver needs additional header files or libraries in nonstandard +places, the DBDRIVER_INCLUDES and DBDRIVER_LIBS lines should also be +updated. + +Calls to dns_sdb_register() and dns_sdb_unregister() (or wrappers, +e.g. timedb_init() and timedb_clear() for the timedb sample sdb +driver) must be inserted into the server, in bind9/bin/named/main.c. +Registration should be in setup(), before the call to +ns_server_create(). Unregistration should be in cleanup(), +after the call to ns_server_destroy(). A #include should be added +corresponding to the driver header file. + +You should try doing this with one or more of the sample drivers +before attempting to write a driver of your own. + + +Configuring the Server + +To make a zone use a new database driver, specify a "database" option +in its "zone" statement in named.conf. For example, if the driver +registers itself under the name "acmedb", you might say + + zone "foo.com" { + database "acmedb"; + }; + +You can pass arbitrary arguments to the create() function of the +driver by adding any number of whitespace-separated words after the +driver name: + + zone "foo.com" { + database "acmedb -mode sql -connect 10.0.0.1"; + }; + + +Hints for Driver Writers + + - If a driver is generating data on the fly, it probably should + not implement the allnodes() function, since a zone transfer + will not be meaningful. The allnodes() function is more relevant + with data from a database. + + - The authority() function is necessary if and only if the lookup() + function will not add SOA and NS records at the zone apex. If + SOA and NS records are provided by the lookup() function, + the authority() function should be NULL. + + - When a driver is registered, an opaque object can be provided. This + object is passed into the database create() and destroy() functions. + + - When a database is created, an opaque object can be created that + is associated with that database. This object is passed into the + lookup(), authority(), and allnodes() functions, and is + destroyed by the destroy() function. + + +Future Directions + +A future release may support dynamic loading of sdb drivers. + + +$Id: sdb,v 1.5.206.1 2004/03/06 13:16:20 marka Exp $ |