Information for Netatalk Developers =================================== For basic installation instructions, see the INSTALL file. Netatalk is an implementation of "AFP over TCP". Netatalk also support the AppleTalk Protocol Suite for legacy Macs. The current release contains support for EtherTalk Phase I and II, DDP, RTMP, NBP, ZIP, AEP, ATP, PAP, ASP, AFP and DSI. The complete stack looks like this on a BSD-derived system: AFP AFP | | ASP PAP DSI \ / | ATP RTMP NBP ZIP AEP | | | | | | | -+---------------------------------------------------+- (kernel boundary) | Socket | +-----------------------+------------+--------------+ | | TCP | UDP | | DDP +------------+--------------+ | | IP | +-----------------------+---------------------------+ | Network-Interface | +---------------------------------------------------+ DSI is a session layer used to carry AFP over TCP. DDP is in the kernel. "atalkd" implements RTMP, NBP, ZIP, and AEP. It is the AppleTalk equivalent of Unix "routed". There is also a client-stub library for NBP. ATP and ASP are implemented as libraries. "papd" allows Macs to spool to "lpd", and "pap" allows Unix machines to print to AppleTalk connected printers. "psf" is a PostScript printer filter for "lpd", designed to use "pap". "psorder" is a PostScript reverser, called by "psf" to reverse pages printed to face-up stacking printers. "afpd" provides Macs with an interface to the Unix file system. Refer to the appropriate man pages for operational information. Compilation =========== The `configure' shell script attempts to guess correct values for various system-dependent variables used during compilation. It uses those values to create a `Makefile' in each directory of the package. It may also create one or more `.h' files containing system-dependent definitions. Finally, it creates a shell script `config.status' that you can run in the future to recreate the current configuration, a file `config.cache' that saves the results of its tests to speed up reconfiguring, and a file `config.log' containing compiler output (useful mainly for debugging `configure'). If you need to do unusual things to compile the package, please try to figure out how `configure' could check whether to do them, and mail diffs or instructions to the address given in the `README' so they can be considered for the next release. If at some point `config.cache' contains results you don't want to keep, you may remove or edit it. The file `configure.in' is used to create `configure' by a program called `autoconf'. You only need `configure.in' if you want to change it or regenerate `configure' using a newer version of `autoconf'. Tools for Developers ==================== 1. Libtool Libtool encapsulates the platform specific dependencies for the creation of libraries. It determines if the local platform can support shared libraries or if it only supports static libraries. Documentation: http://www.gnu.org/software/libtool/ 2. GNU m4 GNU m4 is an implementation of the Unix macro processor. It reads stdin and copies to stdout expanding defined macros as it processes the text. Documentation: http://www.gnu.org/software/m4/ 3. Autoconf Autoconf is a package of m4 macros that produce shell scripts to configure source code packages. Documentation: http://www.gnu.org/software/autoconf/ 4. Automake Automake is a tool that generates 'Makefile.in' files. Documentation: http://www.gnu.org/software/automake/ Optional ======== 5. OpenSSL and/or Libgcrypt The OpenSSL Project is a collaborative effort to develop a robust, commercial-grade, full-featured, and Open Source toolkit implementing the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) protocols as well as a full-strength general purpose cryptography library. This is required to enable DHX login support. Get everything at http://www.openssl.org/ The Libgcrypt is a general purpose cryptographic library based on the code from GnuPG. This is required to enable DHX2 login support. Get everything at http://directory.fsf.org/project/libgcrypt/ 6. TCP Wrappers Wietse Venema's network logger, also known as TCPD or LOG_TCP. These programs log the client host name of incoming telnet, ftp, rsh, rlogin, finger etc. requests. Security options are: access control per host, domain and/or service; detection of host name spoofing or host address spoofing; booby traps to implement an early-warning system. TCP Wrappers can be gotten at ftp://ftp.porcupine.org/pub/security/ Netatalk uses TCP Wrappers to authorize host access when using afpovertcp. It should be noted that if DDP is in use, the connection will still be allowed as TCP Wrappers do not impact DDP connections. 7. PAM (Pluggable Authentication Modules) PAM provides a flexible mechanism for authenticating users. PAM was invented by SUN Microsystems. Author: Andrew Morgan Linux-PAM is a suite of shared libraries that enable the local system administrator to choose how applications authenticate users. You can get the Linux PAM documentation and sources from http://www.kernel.org/pub/linux/libs/pam/ Netatalk also supports other standard PAM implementations such as OpenPAM. 8. Berkeley DB Berkeley DB is a programmatic toolkit that provides fast, reliable, scalable, and mission-critical database support to software developers. BDB can downloaded from http://www.oracle.com/database/berkeley-db/index.html Netatalk's CNID database uses the library and header files from BDB. Currently, Netatalk supports BDB 4.6 and later. Error checking and logging ========================== We wan't rigid error checking and concise log messages. This often leads to signifant code bloat where the relevant function call is buried in error checking and logging statements. In order to alleviate error checking and code readability, we provide a set of error checking macros in . These macros compare the return value of statements againt 0, NULL, -1 (and maybe more, check it out). Every macro comes in four flavours: EC_CHECK, EC_CHECK_LOG, EC_CHECK_LOG_ERR and EC_CHECK_CUSTOM: - EC_CHECK just checks the CHECK - EC_CHECK_LOG additionally logs the stringified function call. - EC_CHECK_LOG_ERR allows specifying the return value - EC_CHECK_CUSTOM allows custom actions The macros EC_CHECK* unconditionally jump to a cleanup label where the neccessary cleanup can be done alongside controlling the return value. EC_CHECK_CUSTOM doesn't do that, so an extra "goto EC_CLEANUP" may be performed as appropiate. Example: - stat() without EC macro: static int func(const char *name) { int ret = 0; ... if ((ret = stat(name, &some_struct_stat)) != 0) { LOG(...); ret = -1; /* often needed to explicitly set the error indicating return value */ goto cleanup; } return ret; cleanup: ... return ret; } - stat() with EC macro: static int func(const char *name) { EC_INIT; /* expands to int ret = 0; */ char *uppername = NULL EC_NULL(uppername = strdup(name)); EC_ZERO(strtoupper(uppername)); EC_ZERO(stat(uppername, &some_struct_stat)); /* expands to complete if block from above */ EC_STATUS(0); EC_CLEANUP: if (uppername) free(uppername); EC_EXIT; } A boileplate function template is: int func(void) { EC_INIT; ...your code here... EC_STATUS(0); EC_CLEANUP: EC_EXIT; } Ini Parser ========== The ini parser is taken from . It has been slightly modified: - case-sensitive - "include" directive added - iniparser_getstrdup() to complemnt iniparser_getstring(), it return allocated strings which the caller must free as necessary - the API has been modifed such that all iniparser_get* funcs take a section and a parameter as sepereta args instead of one string of the form "section:parameter" in the original library CNID Database Daemons ===================== The CNID database daemons cnid_metad and cnid_dbd are a implementation of the netatalk CNID database support that attempts to put all functionality into separate daemons. There is one cnid_dbd daemon per netatalk volume. The underlying database structure is based on Berkeley DB and the database format is the same as in the cdb CNID backend, so this can be used as a drop-in replacement. Advantages: - No locking issues or leftover locks due to crashed afpd daemons any more. Since there is only one thread of control accessing the database, no locking is needed and changes appear atomic. - Berkeley DB transactions are difficult to get right with several processes attempting to access the CNID database simultanously. This is much easier with a single process and the database can be made nearly crashproof this way (at a performance cost). - No problems with user permissions and access to underlying database files, the cnid_dbd process runs under a configurable user ID that normally also owns the underlying database and can be contacted by whatever afpd daemon accesses a volume. - If an afpd process crashes, the CNID database is unaffected. If the process was making changes to the database at the time of the crash, those changes will be rolled back entirely (transactions). If the process was not using the database at the time of the crash, no corrective action is necessary. In any case, database consistency is assured. Disadvantages: - Performance in an environment of processes sharing the database (files) is potentially better for two reasons: i) IPC overhead. ii) r/o access to database pages is possible by more than one process at once, r/w access is possible for nonoverlapping regions. The current implementation of cnid_dbd uses unix domain sockets as the IPC mechanism. While this is not the fastest possible method, it is very portable and the cnid_dbd IPC mechanisms can be extended to use faster IPC (like mmap) on architectures where it is supported. As a ballpark figure, 20000 requests/replies to the cnid_dbd daemon take about 0.6 seconds on a Pentium III 733 Mhz running Linux Kernel 2.4.18 using unix domain sockets. The requests are "empty" (no database lookups/changes), so this is just the IPC overhead. I have not measured the effects of the advantages of simultanous database access. Installation and configuration There are two executeables that will be built in etc/cnid_dbd and installed into the systems binaries directories of netatalk cnid_metad and cnid_dbd. cnid_metad should run all the time with root permissions. It will be notified when an instance of afpd starts up and will in turn make sure that a cnid_dbd daemon is started for the volume that afpd wishes to access. The cnid_dbd daemon runs as long as necessary and services any other instances of afpd that access the volume. You can safely kill it with SIGTERM, it will be restarted automatically by cnid_metad as soon as the volume is accessed again. cnid_dbd changes to the Berkeley DB directory on startup and sets effective UID and GID to owner and group of that directory. Database and supporting files should therefore be writeable by that user/group. Current shortcomings: - The parameter file parsing of db_param is very simpleminded. It is easy to cause buffer overruns and the like. Also, there is no support for blanks (or weird characters) in filenames for the usock_file parameter. - There is no protection against a malicious user connecting to the cnid_dbd socket and changing the database.