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NSDISPATCH (3) | C library functions | Unix Manual Pages | :man

NAME

nsdispatch - name-service switch dispatcher routine

CONTENTS

Library
Synopsis
Description
Valid source types
Method return values
See Also
History
Authors

LIBRARY


.Lb libc

SYNOPSIS


.In sys/types.h
.In stdarg.h
.In nsswitch.h int
.Fo nsdispatch "void *retval" "const ns_dtab dtab[]" "const char *database" "const char *method_name" "const ns_src defaults[]" "..."
.Fc

DESCRIPTION

The nsdispatch function invokes the methods specified in dtab in the order given by nsswitch.conf(5) for the database database until a successful entry is found.

retval is passed to each method to modify as necessary, to pass back results to the caller of nsdispatch.

Each method has the function signature described by the typedef:

typedef int *nss_method "void *retval" "void *mdata" "va_list *ap";

dtab is an array of ns_dtab structures, which have the following format:
typedef struct _ns_dtab {
const char *src;
nss_method method;
void *mdata;
} ns_dtab;


The

dtab
array should consist of one entry for each source type that is
implemented, with

src
as the name of the source,

method
as a function which handles that source, and

mdata
as a handle on arbitrary data to be passed to the method.
The last entry in

dtab
should contain

NULL
values for

src,

method,
and

mdata.

Additionally, methods may be implemented in NSS modules, in which case they are selected using the database and method_name arguments along with the configured source. (The methods supplied via dtab take priority over those implemented in NSS modules in the event of a conflict.)

defaults contains a list of default sources to try if nsswitch.conf(5) is missing or corrupted, or if there is no relevant entry for database. It is an array of ns_src structures, which have the following format:
typedef struct _ns_src {
const char *src;
u_int32_t flags;
} ns_src;


The

defaults
array should consist of one entry for each source to be configured by
default indicated by

src,
and

flags
set to the criterion desired
(usually

NS_SUCCESS;
refer to

Method return values
for more information).
The last entry in

defaults
should have

src
set to

NULL
and

flags
set to 0.


For convenience, a global variable defined as:

extern const ns_src __nsdefaultsrc[];



exists which contains a single default entry for the source

'files'
that may be used by callers which do not require complicated default
rules.

'...' are optional extra arguments, which are passed to the appropriate method as a variable argument list of the type
.Vt va_list .

Valid source types

While there is support for arbitrary sources, the following #defines for commonly implemented sources are available:
"#define value"
NSSRC_FILES "" "files" "
NSSRC_DNS "" "dns" "
NSSRC_NIS "" "nis" "
NSSRC_COMPAT "" "compat" "

Refer to nsswitch.conf(5) for a complete description of what each source type is.

Method return values

The
.Vt nss_method functions must return one of the following values depending upon status of the lookup:
"Return value Status code"
NS_SUCCESS success
NS_NOTFOUND notfound
NS_UNAVAIL unavail
NS_TRYAGAIN tryagain
NS_RETURN -none-

Refer to nsswitch.conf(5) for a complete description of each status code.

The nsdispatch function returns the value of the method that caused the dispatcher to terminate, or NS_NOTFOUND otherwise.

SEE ALSO

hesiod(3), stdarg(3), nsswitch.conf(5), yp(8)

HISTORY

AUTHORS


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