xref: /illumos-gate/usr/src/lib/libgss/README.spi (revision ddcb6370)
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24
25	The Service Provider Interface for libgss and its Mechanisms
26	------------------------------------------------------------
27
281.  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
402.  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
703.  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.
113