minix/lib/libc/yp/ypclnt.3

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.Dd March 2, 2012
.Dt YPCLNT 3
.Os
.Sh NAME
.Nm yp_all ,
.Nm yp_bind ,
.Nm yp_first ,
.Nm yp_get_default_domain ,
.Nm yp_master ,
.Nm yp_match ,
.Nm yp_next ,
.Nm yp_order ,
.Nm yp_unbind ,
.Nm yperr_string ,
.Nm ypprot_err
.Nm yp_setbindtries
.Nd Interface to the YP subsystem
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In rpc/rpc.h
.In rpcsvc/ypclnt.h
.In rpcsvc/yp_prot.h
.Ft int
.Fn yp_all "const char *indomain" "const char *inmap" "struct ypall_callback *incallback"
.Ft int
.Fn yp_bind "const char *dom"
.Ft int
.Fn yp_first "const char *indomain" "const char *inmap" "char **outkey" "int *outkeylen" "char **outval" "int *outvallen"
.Ft int
.Fn yp_get_default_domain "char **outdomain"
.Ft int
.Fn yp_master "const char *indomain" "const char *inmap" "char **outname"
.Ft int
.Fn yp_match "const char *indomain" "const char *inmap" "const char *inkey" "int inkeylen" "char **outval" "int *outvallen"
.Ft int
.Fn yp_next "const char *indomain" "const char *inmap" "const char *inkey" "int inkeylen" "char **outkey" "int *outkeylen" "char **outval" "int *outvallen"
.Ft int
.Fn yp_order "const char *indomain" "const char *inmap" "int *outorder"
.Ft void
.Fn yp_unbind "const char *dom"
.Ft char *
.Fn yperr_string "int incode"
.Ft int
.Fn ypprot_err "unsigned int incode"
.Ft int
.Fn yp_setbindtries "int ntries"
.Sh DESCRIPTION
The
.Nm ypclnt
suite provides an interface to the
.Tn YP
subsystem.
For a general description of the
.Tn YP
subsystem, see
.Xr yp 8 .
.Pp
For all functions, input values begin with
.Pa in
and output values begin with
.Pa out .
.Pp
Any output values of type
.Em char **
should be the addresses of uninitialized character pointers.
These values will be reset to the null pointer (unless the address
itself is the null pointer, in which case the error
.Er YPERR_BADARGS
will be returned).
If necessary,
memory will be allocated by the
.Tn YP
client routines using
.Fn malloc ,
and the result will be stored in the appropriate output value.
If the invocation of a
.Tn YP
client routine doesn't return an error,
and an output value is not the null pointer, then this memory
should be freed by the user when there is no additional need for
the data stored there.
For
.Pa outkey
and
.Pa outval ,
two extra bytes of memory are allocated for a
.Ql \en
and
.Ql \e0 ,
which are not
reflected in the values of
.Pa outkeylen
or
.Pa outvallen .
.Pp
All occurrences of
.Pa indomain
and
.Pa inmap
must be non-null, NUL-terminated strings.
All input strings which also have
a corresponding length parameter cannot be the null pointer unless the
corresponding length value is zero.
Such strings need not be NUL-terminated.
.Pp
All
.Tn YP
lookup calls (the functions
.Fn yp_all ,
.Fn yp_first ,
.Fn yp_master ,
.Fn yp_match ,
.Fn yp_next ,
.Fn yp_order )
require a
.Tn YP
domain name and a
.Tn YP
map name.
The default domain name may be obtained by calling
.Fn yp_get_default_domain ,
and should thus be used before all other
.Tn YP
calls in a client program.
The value it places
.Pa outdomain
is suitable for use as the
.Pa indomain
parameter to all subsequent
.Tn YP
calls.
.Pp
In order for
.Tn YP
lookup calls to succeed, the client process must be bound
to a
.Tn YP
server process.
The client process need not explicitly bind to
the server, as it happens automatically whenever a lookup occurs.
The function
.Fn yp_bind
is provided for a backup strategy, e.g. a local file, when a
.Tn YP
server process is not available.
Each binding uses one socket descriptor on the client
process, which may be explicitly freed using
.Fn yp_unbind ,
which frees all per-process and per-node resources to bind the domain and
marks the domain unbound.
.Pp
If, during a
.Tn YP
lookup, an RPC failure occurs, the domain used in the lookup
is automatically marked unbound and the
.Nm ypclnt
layer retries the lookup as long as
.Xr ypbind 8
is running and either the client process cannot bind to a server for the domain
specified in the lookup, or RPC requests to the
.Tn YP
server process fail.
If an error is not RPC-related, one of the
.Tn YP
error codes described below
is returned and control given back to the user code.
.Pp
The
.Nm ypclnt
suite provides the following functionality:
.Bl -tag -width yp_matchxxxx
.It Fn yp_match
Provides the value associated with the given key.
.It Fn yp_first
Provides the first key-value pair from the given map in the named domain.
.It Fn yp_next
Provides the next key-value pair in the given map.
To obtain the second pair,
the
.Pa inkey
value should be the
.Pa outkey
value provided by the initial call to
.Fn yp_first .
In the general case, the next key-value pair may be obtained by using the
.Pa outkey
value from the previous call to
.Fn yp_next
as the value for
.Pa inkey .
.Pp
Of course, the notions of
.Dq first
and
.Dq next
are particular to the
type of
.Tn YP
map being accessed, and thus there is no guarantee of lexical order.
The only guarantees provided with
.Fn yp_first
and
.Fn yp_next ,
providing that the same map on the same server is polled repeatedly until
.Fn yp_next
returns YPERR_NOMORE, are that all key-value pairs in that map will be accessed
exactly once, and if the entire procedure is repeated, the order will be
the same.
.Pp
If the server is heavily loaded or the server fails for some reason, the
domain being used may become unbound.
If this happens, and the client process re-binds, the retrieval rules
will break: some entries may be seen twice, and others not at all.
For this reason, the function
.Fn yp_all
provides a better solution for reading all of the entries in a particular map.
.It Fn yp_all
This function provides a way to transfer an entire map from
the server to the client process with a single request.
This transfer uses TCP, unlike all other functions in the
.Nm ypclnt
suite, which use UDP.
The entire transaction occurs in a single RPC request-response.
The third argument to this function provides a way to supply
the name of a function to process each key-value pair in the map.
.Fn yp_all
returns after the entire transaction is complete, or the
.Pa foreach
function decides that it does not want any more key-value pairs.
The third argument to
.Fn yp_all
is:
.Bd -literal -offset indent
struct ypall_callback *incallback {
	int (*foreach)();
	char *data;
};
.Ed
.Pp
The
.Em char *data
argument is an opaque pointer for use by the callback function.
The
.Pa foreach
function should return non-zero when it no longer wishes to process
key-value pairs, at which time
.Fn yp_all
returns a value of 0, and is called with the following arguments:
.Pp
.Bd -literal -offset indent
int foreach (
	int instatus,
	char *inkey,
	int inkeylen,
	char *inval,
	int invallen,
	char *indata
);
.Ed
.Pp
Where:
.Bl -tag -width "inkey, inval"
.It Fa instatus
Holds one of the return status values described in
.In rpcsvc/yp_prot.h :
see
.Fn ypprot_err
below for a function that will translate
.Tn YP
protocol errors into a
.Nm ypclnt
layer error code as described in
.In rpcsvc/ypclnt.h .
.It Fa inkey, inval
The key and value arguments are somewhat different here than described
above.
In this case, the memory pointed to by
.Fa inkey
and
.Fa inval
is private to
.Fn yp_all ,
and is overwritten with each subsequent key-value pair, thus the
.Pa foreach
function should do something useful with the contents of that memory during
each iteration.
If the key-value pairs are not terminated with either
.Ql \en
or
.Ql \e0
in the map, then they will not be terminated as such when given to the
.Pa foreach
function, either.
.It Fa indata
This is the contents of the
.Pa incallback-\*[Gt]data
element of the callback structure.
It is provided as a means to share state between the
.Pa foreach
function and the user code.
Its use is completely optional: cast it to
something useful or simply ignore it.
.El
.It Fn yp_order
Returns the order number for a map.
.It Fn yp_master
Returns the hostname for the machine on which the master
.Tn YP
server process for
a map is running.
.It Fn yperr_string
Returns a pointer to a NUL-terminated error string that does not contain a
.Ql \&.
or
.Ql \en .
.It Fn ypprot_err
Converts a
.Tn YP
protocol error code to a
.Nm ypclnt
error code suitable for
.Fn yperr_string .
.It Fn yp_setbindtries
Set the number of tries to attempt to bind to the domain before returning
an error.
The default is
.Dv 0
which means wait forever if no ypserver is not found of if the RPC
communication with the yp server fails.
If the number passed is negative, the current number of tries is not modified.
.Pp
This function is an extention to the client library that allows application
to catch communication problems with the ypserver without blocking forever.
.El
.Sh RETURN VALUES
All functions in the
.Nm ypclnt
suite which are of type
.Em int
return 0 upon success or one of the following error codes upon failure:
.Bl -tag -width "YPERR_BADARGS   "
.It Bq Er YPERR_BADARGS
The passed arguments to the function are invalid.
.It Bq Er YPERR_BADDB
The
.Tn YP
map that was polled is defective.
.It Bq Er YPERR_DOMAIN
Client process cannot bind to server on this
.Tn YP
domain.
.It Bq Er YPERR_KEY
The key passed does not exist.
.It Bq Er YPERR_MAP
There is no such map in the server's domain.
.It Bq Er YPERR_DOM
The local
.Tn YP
domain is not set.
.It Bq Er YPERR_NOMORE
There are no more records in the queried map.
.It Bq Er YPERR_PMAP
Cannot communicate with portmapper (see
.Xr rpcbind 8 ) .
.It Bq Er YPERR_RESRC
A resource allocation failure occurred.
.It Bq Er YPERR_RPC
An RPC failure has occurred.
The domain has been marked unbound.
.It Bq Er YPERR_VERS
Client/server version mismatch.
If the server is running version 1 of the
.Tn YP
protocol,
.Fn yp_all
functionality does not exist.
.It Bq Er YPERR_BIND
Cannot communicate with
.Xr ypbind 8 .
.It Bq Er YPERR_YPERR
An internal server or client error has occurred.
.It Bq Er YPERR_YPSERV
The client cannot communicate with the
.Tn YP
server process.
.El
.Sh SEE ALSO
.Xr malloc 3 ,
.Xr yp 8 ,
.Xr ypbind 8 ,
.Xr ypserv 8
.Sh AUTHORS
.An Theo De Raadt