$FreeBSD: head/lib/libc/net/nsdispatch.3 108317 2002-12-27 12:15:40Z schweikh $
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.Dd January 19, 1999 .Dt NSDISPATCH 3 .Os .Sh NAME .Nm nsdispatch .Nd name-service switch dispatcher routine .Sh LIBRARY .Lb libc .Sh SYNOPSIS n nsswitch.h .Ft int .Fo nsdispatch .Fa "void *retval" .Fa "const ns_dtab dtab[]" .Fa "const char *database" .Fa "const char *method" .Fa "const ns_src defaults[]" .Fa "..." .Fc .Sh DESCRIPTION The .Fn nsdispatch function invokes the callback functions specified in .Va dtab in the order given in
a /etc/nsswitch.conf for the database .Va database until a successful entry is found.
p .Va retval is passed to each callback function to modify as necessary (to pass back to the caller of .Fn nsdispatch )
p .Va dtab is an array of .Va ns_dtab structures, which have the following format: d -literal -offset indent typedef struct { const char *src; int (*cb)(void *retval, void *cb_data, va_list ap); void *cb_data; } ns_dtab; .Ed
p d -ragged -offset indent For each source type that is implemented, an entry with .Va src set to the name of the source, .Va cb defined as a function which handles that source, and .Va cb_data is used to pass arbitrary data to the callback function. The last entry in .Va dtab should contain .Dv NULL values for .Va src , .Va cb , and .Va cb_data . .Ed
p .Va method is usually the name of the function calling .Fn nsdispatch . When dynamic loading is supported, a symbol constructed from .Va database , the current source, and .Va method will be used as the name to invoke the dynamically loaded function.
p .Va defaults contains a list of default sources to try in the case of a missing or corrupt .Xr nsswitch.conf 5 , or if there isn't a relevant entry for .Va database . It is an array of .Va ns_src structures, which have the following format: d -literal -offset indent typedef struct { const char *src; u_int32_t flags; } ns_src; .Ed
p d -ragged -offset indent For each default source type, an entry with .Va src set to the name of the source, and .Va flags set to the relevant flags (usually .Dv NS_SUCCESS ; refer to .Sx Callback return values for more information). The last entry in .Va defaults should have .Va src set to .Dv NULL and .Va flags set to 0.
p For convenience, a global variable defined as: .Dl extern const ns_src __nsdefaultsrc[]; exists which contains a single default entry for .Sq files for use by callers which don't require complicated default rules. .Ed
p .Sq Va ... are optional extra arguments, which are passed to the appropriate callback function as a variable argument list of the type .Va va_list . .Ss Valid source types Whilst there is support for arbitrary sources, the following #defines for commonly implemented sources are available: l -column NS_COMPAT COMPAT -offset indent t Sy "#define value" t "NSSRC_FILES ""files""" t "NSSRC_DNS ""dns""" t "NSSRC_NIS ""nis""" t "NSSRC_COMPAT ""compat""" .El
p Refer to .Xr nsswitch.conf 5 for a complete description of what each source type is.
p .Ss Callback return values The callback functions should return one of the following values depending upon status of the lookup: l -column NS_NOTFOUND -offset indent t Sy "Return value Status code" t "NS_SUCCESS success" t "NS_NOTFOUND notfound" t "NS_UNAVAIL unavail" t "NS_TRYAGAIN tryagain" .El
p Refer to .Xr nsswitch.conf 5 for a complete description of what each status code is.
p .Nm returns the value of the callback that caused the dispatcher to finish, or NS_NOTFOUND otherwise. .Sh SEE ALSO .Xr hesiod 3 , .Xr stdarg 3 , .Xr ypclnt 3 , .Xr nsswitch.conf 5 .Sh HISTORY The .Nm routines first appeared in .Fx 5.0 . They were imported from the .Nx Project, where they appeared first in .Nx 1.4 . .Sh AUTHORS Luke Mewburn .Aq lukem@netbsd.org wrote this freely distributable name-service switch implementation, using ideas from the .Tn ULTRIX .Xr svc.conf 5 and .Tn Solaris .Xr nsswitch.conf 4 manual pages. .Sh BUGS The .Nm routines are not thread safe. This will be rectified in the future.
p Currently there is no support for dynamically loadable dispatcher callback functions. It is anticipated that this will be added in the future in the back-end without requiring changes to code that invokes .Fn nsdispatch .