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/**
 ** loginrec.c:  platform-independent login recording and lastlog retrieval
 **/

/* For now lastlog code has been removed as it wasn't being used by Dropbear. */

/*
  The new login code explained
  ============================

  This code attempts to provide a common interface to login recording
  (utmp and friends) and last login time retrieval.

  Its primary means of achieving this is to use 'struct logininfo', a
  union of all the useful fields in the various different types of
  system login record structures one finds on UNIX variants.

  We depend on autoconf to define which recording methods are to be
  used, and which fields are contained in the relevant data structures
  on the local system. Many C preprocessor symbols affect which code
  gets compiled here.

  The code is designed to make it easy to modify a particular
  recording method, without affecting other methods nor requiring so
  many nested conditional compilation blocks as were commonplace in
  the old code.

  For login recording, we try to use the local system's libraries as
  these are clearly most likely to work correctly. For utmp systems
  this usually means login() and logout() or setutent() etc., probably
  in libutil, along with logwtmp() etc. On these systems, we fall back
  to writing the files directly if we have to, though this method
  requires very thorough testing so we do not corrupt local auditing
  information. These files and their access methods are very system
  specific indeed.

  For utmpx systems, the corresponding library functions are
  setutxent() etc. To the author's knowledge, all utmpx systems have
  these library functions and so no direct write is attempted. If such
  a system exists and needs support, direct analogues of the [uw]tmp
  code should suffice.

  Retrieving the time of last login ('lastlog') is in some ways even
  more problemmatic than login recording. Some systems provide a
  simple table of all users which we seek based on uid and retrieve a
  relatively standard structure. Others record the same information in
  a directory with a separate file, and others don't record the
  information separately at all. For systems in the latter category,
  we look backwards in the wtmp or wtmpx file for the last login entry
  for our user. Naturally this is slower and on busy systems could
  incur a significant performance penalty.

  Calling the new code
  --------------------

  In OpenSSH all login recording and retrieval is performed in
  login.c. Here you'll find working examples. Also, in the logintest.c
  program there are more examples.

  Internal handler calling method
  -------------------------------

  When a call is made to login_login() or login_logout(), both
  routines set a struct logininfo flag defining which action (log in,
  or log out) is to be taken. They both then call login_write(), which
  calls whichever of the many structure-specific handlers autoconf
  selects for the local system.

  The handlers themselves handle system data structure specifics. Both
  struct utmp and struct utmpx have utility functions (see
  construct_utmp*()) to try to make it simpler to add extra systems
  that introduce new features to either structure.

  While it may seem terribly wasteful to replicate so much similar
  code for each method, experience has shown that maintaining code to
  write both struct utmp and utmpx in one function, whilst maintaining
  support for all systems whether they have library support or not, is
  a difficult and time-consuming task.

  Lastlog support proceeds similarly. Functions login_get_lastlog()
  (and its OpenSSH-tuned friend login_get_lastlog_time()) call
  getlast_entry(), which tries one of three methods to find the last
  login time. It uses local system lastlog support if it can,
  otherwise it tries wtmp or wtmpx before giving up and returning 0,
  meaning "tilt".

  Maintenance
  -----------

  In many cases it's possible to tweak autoconf to select the correct
  methods for a particular platform, either by improving the detection
  code (best), or by presetting DISABLE_<method> or CONF_<method>_FILE
  symbols for the platform.

  Use logintest to check which symbols are defined before modifying
  configure.ac and loginrec.c. (You have to build logintest yourself
  with 'make logintest' as it's not built by default.)

  Otherwise, patches to the specific method(s) are very helpful!

*/

/**
 ** TODO:
 **   homegrown ttyslot()
 **   test, test, test
 **
 ** Platform status:
 ** ----------------
 **