nsdispatch -- name-service switch dispatcher routine
Standard C Library (libc, -lc)
#include <sys/types.h>
#include <stdarg.h>
#include <nsswitch.h>
int
nsdispatch(void *retval, const ns_dtab dtab[], const char *database,
const char *method_name, const ns_src defaults[], ...);
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 va_list.
Valid source types [Toc] [Back]
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 [Toc] [Back]
The 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.
hesiod(3), stdarg(3), nsswitch.conf(5), yp(8)
The nsdispatch() function first appeared in FreeBSD 5.0. It was imported
from the NetBSD Project, where it appeared first in NetBSD 1.4. Support
for NSS modules first appeared in FreeBSD 5.1.
Luke Mewburn <lukem@netbsd.org> wrote this freely-distributable name-service
switch implementation, using ideas from the ULTRIX svc.conf(5) and
Solaris nsswitch.conf(4) manual pages. The FreeBSD Project added the
support for threads and NSS modules, and normalized the uses of
nsdispatch() within the standard C library.
FreeBSD 5.2.1 April 16, 2003 FreeBSD 5.2.1 [ Back ] |
