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25 The Service Provider Interface for libgss and its Mechanisms
281. The libgss SPI upto 11/2004
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).
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).
402. The libgss SPI after PSARC 2004/810
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:
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
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;
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.
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().
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.
703. The Future libgss SPI
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.
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.
81 We can then rename all mechanisms' methods from <mech>_<gss-func> to
82 <gss-func>. The corresponding typedefs will be renamed to
85 The SPI, then, will be almost exactly the same as the API.
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.
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).
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.
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().
105 Mechanisms that do not provide the old method registration function
106 will be loaded as follows:
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.
112 - libgss will dlsym() each mechanism provider SPI method.