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  13  When distributing Covered Code, include this CDDL HEADER in each
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  15  If applicable, add the following below this CDDL HEADER, with the
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  19  CDDL HEADER END
  20 
  21  Copyright 2010 Sun Microsystems, Inc.  All rights reserved.
  22  Use is subject to license terms.
  23 
  24 
  25         The Service Provider Interface for libgss and its Mechanisms
  26         ------------------------------------------------------------
  27 
  28 1.  The libgss SPI upto 11/2004
  29 
  30     Prior to PSARC 2004/810 the libgss SPI consisted of a function
  31     provided by each mechanism whose return value is a pointer to a
  32     structure full of references to the mechanism's entry points
  33     (hereinafter: methods).
  34 
  35     This structure does not include any hooks for versioning, which
  36     means that additions of any mechanism methods at micro/patch
  37     releases require patching libgss.so.1 and all the GSS mechanisms
  38     shipped with Solaris (Kerberos V, DH, SPNEGO).
  39 
  40 2.  The libgss SPI after PSARC 2004/810
  41 
  42     In order to avoid changing the gss_config struct and patching all
  43     three mechanisms (four, if the dummy mech counts) and libgss
  44     together and in anticipation of a cleaner SPI in the future (see
  45     next section) the SPI after PSARC 2004/810 will be as before but
  46     supplemented as follows:
  47 
  48      - any new SPI mechanism methods will NOT be placed in gss_config,
  49        instead there is a new gss_config_ext structure, which is to be
  50        used _only_ by libgss (to avoid struct versioning and/or patch
  51        issues), which should be extended to have a pointer to the new
  52        method;
  53 
  54      - there is a new libgss function, __gss_get_mechanism_ext(), which
  55        is used to get at the gss_config_ext for a mechanism;
  56 
  57      - __gss_get_mechanism_ext() uses dlsym() to build the
  58        gss_config_ext struct for the mech by individually loading each
  59        and every mechanism method that isn't part of the old gss_config
  60        struct -- this happens only once per-method, of course; the
  61        result is cached.
  62 
  63        The symbol names that are dlsym()ed are of the form gssspi_* and
  64        correspond to gss_*; e.g., gssspi_acquire_cred_with_password().
  65 
  66        New methods also have a corresponding typedef named
  67        <gss_func>_sfct -- the 's' in 'sfct' is for "SPI" and the 'fct'
  68        is for "function."  This is used to keep cast expressions short.
  69 
  70 3.  The Future libgss SPI
  71 
  72     Once the Solaris krb5 source is resync'ed with MIT krb5 1.4 there
  73     will be no further need for the 'void *context' argument to all the
  74     libgss mechanisms' methods.
  75 
  76     At that point it will be possible to remove this 'void *context'
  77     argument from all the libgss SPI function prototypes, the main
  78     result of which will be that the mechanisms' methods will then have
  79     the same function signature as the corresponding GSS-API functions.
  80 
  81     We can then rename all mechanisms' methods from <mech>_<gss-func> to
  82     <gss-func>.  The corresponding typedefs will be renamed to
  83     <gss-func>_fct.
  84 
  85     The SPI, then, will be almost exactly the same as the API.
  86 
  87     There will be some minor differences, primarily that some API
  88     functions won't have a corresponding SPI method, such as
  89     gss_release_buffer(3GSS), for example.
  90 
  91     Some time later we may open the SPI to third party implementors;
  92     this could be particularly useful as a way to get access to 3rd
  93     party implementations of SPKM and LIPKEY (assuming any ever exist --
  94     SPKM's is a very problematic specification).
  95 
  96     Third party mechanisms should just export all the symbols for the
  97     GSS-API functions, like MIT krb5 does, but functions which libgss
  98     won't call (e.g., gss_release_buffer(3GSS)) should either not be
  99     implemented or should be weak symbols.
 100 
 101     Solaris native mechanisms may still provide the mechanism method
 102     registration function as usual for optimization purposes -- to
 103     reduce the number of calls to dlsym().
 104 
 105     Mechanisms that do not provide the old method registration function
 106     will be loaded as follows:
 107 
 108      - libgss will look for and find the mechanism's
 109        GSS_Indicate_mechs() method and will call it to discover the
 110        mechanism provider's mechanism OIDs.
 111 
 112      - libgss will dlsym() each mechanism provider SPI method.