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44 .Nd name-service switch dispatcher routine
54 .Fa "const ns_dtab dtab[]"
55 .Fa "const char *database"
56 .Fa "const char *method_name"
57 .Fa "const ns_src defaults[]"
63 function invokes the methods specified in
69 until a successful entry is found.
72 is passed to each method to modify as necessary, to pass back results to
76 Each method has the function signature described by the typedef:
79 .Fn \*(lp*nss_method\*(rp "void *retval" "void *mdata" "va_list *ap" ;
84 structures, which have the following format:
85 .Bd -literal -offset indent
86 typedef struct _ns_dtab {
93 .Bd -ragged -offset indent
96 array should consist of one entry for each source type that is
99 as the name of the source,
101 as a function which handles that source, and
103 as a handle on arbitrary data to be passed to the method.
115 Additionally, methods may be implemented in NSS modules, in
116 which case they are selected using the
120 arguments along with the configured source.
121 (The methods supplied via
123 take priority over those implemented in NSS modules in the event
127 contains a list of default sources to try if
129 is missing or corrupted, or if there is no relevant entry for
133 structures, which have the following format:
134 .Bd -literal -offset indent
135 typedef struct _ns_src {
141 .Bd -ragged -offset indent
144 array should consist of one entry for each source to be configured by
149 set to the criterion desired
153 .Sx Method return values
154 for more information).
165 For convenience, a global variable defined as:
166 .Dl extern const ns_src __nsdefaultsrc[];
167 exists which contains a single default entry for the source
169 that may be used by callers which do not require complicated default
174 are optional extra arguments, which are passed to the appropriate method
175 as a variable argument list of the type
177 .Ss Valid source types
178 While there is support for arbitrary sources, the following
179 #defines for commonly implemented sources are available:
180 .Bl -column NSSRC_COMPAT compat -offset indent
181 .It Sy "#define value"
182 .It Dv NSSRC_FILES Ta """files""
183 .It Dv NSSRC_DNS Ta """dns""
184 .It Dv NSSRC_NIS Ta """nis""
185 .It Dv NSSRC_COMPAT Ta """compat""
190 for a complete description of what each source type is.
192 .Ss Method return values
195 functions must return one of the following values depending upon status
197 .Bl -column "Return value" "Status code"
198 .It Sy "Return value Status code"
199 .It Dv NS_SUCCESS Ta success
200 .It Dv NS_NOTFOUND Ta notfound
201 .It Dv NS_UNAVAIL Ta unavail
202 .It Dv NS_TRYAGAIN Ta tryagain
203 .It Dv NS_RETURN Ta -none-
208 for a complete description of each status code.
212 function returns the value of the method that caused the dispatcher to
219 .Xr nsswitch.conf 5 ,
224 function first appeared in
226 It was imported from the
229 where it appeared first in
231 Support for NSS modules first appeared in
236 wrote this freely-distributable name-service switch implementation,
247 added the support for threads and NSS modules, and normalized the uses
250 within the standard C library.