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XDR(3)			   Linux Programmers Manual		       XDR(3)



NAME
       xdr - library routines for external data representation

SYNOPSIS AND DESCRIPTION
       These  routines	allow  C programmers to describe arbitrary data struc
       tures in a machine-independent  fashion.   Data	for  remote  procedure
       calls are transmitted using these routines.

       The  prototypes	below  are declared in  and make use of the
       following types:

	   typedef int bool_t;

	   typedef bool_t (*xdrproc_t) (XDR *, void *,...);

       For the declaration of the XDR type, see .

       bool_t xdr_array(XDR *xdrs, char **arrp, unsigned int *sizep,
			unsigned int maxsize, unsigned int elsize,
			xdrproc_t elproc);

	      A  filter  primitive  that  translates  between  variable-length
	      arrays  and  their  corresponding external representations.  The
	      argument arrp is the address of the pointer to the array,  while
	      sizep  is  the  address  of the element count of the array; this
	      element count cannot exceed maxsize.  The argument elsize is the
	      sizeof each of the arrays elements, and elproc is an XDR filter
	      that translates between the array elements C  form,  and	their
	      external	representation.   This	routine returns one if it suc
	      ceeds, zero otherwise.

       bool_t xdr_bool(XDR *xdrs, bool_t *bp);

	      A filter primitive that translates between booleans (C integers)
	      and  their  external  representations.  When encoding data, this
	      filter produces values of either	one  or  zero.	 This  routine
	      returns one if it succeeds, zero otherwise.

       bool_t xdr_bytes(XDR *xdrs, char **sp, unsigned int *sizep,
			unsigned int maxsize);

	      A  filter primitive that translates between counted byte strings
	      and their external representations.   The  argument  sp  is  the
	      address  of  the	string	pointer.   The length of the string is
	      located at address sizep; strings cannot be longer than maxsize.
	      This routine returns one if it succeeds, zero otherwise.

       bool_t xdr_char(XDR *xdrs, char *cp);

	      A  filter  primitive  that  translates  between C characters and
	      their external representations.  This routine returns one if  it
	      succeeds,  zero  otherwise.   Note:  encoded  characters are not
	      packed, and occupy 4 bytes each.	For arrays of  characters,  it
	      is   worthwhile	to   consider	xdr_bytes(),  xdr_opaque()  or
	      xdr_string().

       void xdr_destroy(XDR *xdrs);

	      A macro that invokes the destroy routine associated with the XDR
	      stream, xdrs.  Destruction usually involves freeing private data
	      structures associated with the stream.  Using xdrs after	invok
	      ing xdr_destroy() is undefined.

       bool_t xdr_double(XDR *xdrs, double *dp);

	      A  filter  primitive  that translates between C double precision
	      numbers  and  their  external  representations.	This   routine
	      returns one if it succeeds, zero otherwise.

       bool_t xdr_enum(XDR *xdrs, enum_t *ep);

	      A  filter  primitive  that  translates between C enums (actually
	      integers) and  their  external  representations.	 This  routine
	      returns one if it succeeds, zero otherwise.

       bool_t xdr_float(XDR *xdrs, float *fp);

	      A  filter  primitive  that translates between C floats and their
	      external representations.  This routine returns one if  it  suc
	      ceeds, zero otherwise.

       void xdr_free(xdrproc_t proc, char *objp);

	      Generic  freeing routine.  The first argument is the XDR routine
	      for the object being freed.  The second argument is a pointer to
	      the  object itself.  Note: the pointer passed to this routine is
	      not freed, but what it points to is freed (recursively).

       unsigned int xdr_getpos(XDR *xdrs);

	      A macro that invokes the get-position  routine  associated  with
	      the  XDR stream, xdrs.  The routine returns an unsigned integer,
	      which indicates the position of the XDR byte stream.   A	desir
	      able feature of XDR streams is that simple arithmetic works with
	      this number, although the XDR stream instances need not  guaran
	      tee this.

       long *xdr_inline(XDR *xdrs, int len);

	      A macro that invokes the in-line routine associated with the XDR
	      stream, xdrs.  The routine returns a  pointer  to  a  contiguous
	      piece  of  the  streams  buffer;	len is the byte length of the
	      desired buffer.  Note: pointer is cast to long *.

	      Warning: xdr_inline() may return NULL (0) if it cannot  allocate
	      a contiguous piece of a buffer.  Therefore the behavior may vary
	      among stream instances; it exists for the sake of efficiency.

       bool_t xdr_int(XDR *xdrs, int *ip);

	      A filter primitive that translates between C integers and  their
	      external	representations.   This routine returns one if it suc
	      ceeds, zero otherwise.

       bool_t xdr_long(XDR *xdrs, long *lp);

	      A filter primitive that translates between C long  integers  and
	      their  external representations.	This routine returns one if it
	      succeeds, zero otherwise.

       void xdrmem_create(XDR *xdrs, char *addr, unsigned int size,
			  enum xdr_op op);

	      This routine initializes the XDR stream  object  pointed	to  by
	      xdrs.  The streams data is written to, or read from, a chunk of
	      memory at location addr whose length is no more than size  bytes
	      long.  The op determines the direction of the XDR stream (either
	      XDR_ENCODE, XDR_DECODE, or XDR_FREE).

       bool_t xdr_opaque(XDR *xdrs, char *cp, unsigned int cnt);

	      A filter primitive that translates  between  fixed  size	opaque
	      data  and  its  external representation.	The argument cp is the
	      address of the opaque object, and cnt  is  its  size  in	bytes.
	      This routine returns one if it succeeds, zero otherwise.

       bool_t xdr_pointer(XDR *xdrs, char **objpp,
			  unsigned int objsize, xdrproc_t xdrobj);

	      Like  xdr_reference()  except  that it serializes NULL pointers,
	      whereas xdr_reference() does not.  Thus, xdr_pointer() can  rep
	      resent recursive data structures, such as binary trees or linked
	      lists.

       void xdrrec_create(XDR *xdrs, unsigned int sendsize,
			  unsigned int recvsize, char *handle,
			  int (*readit) (char *, char *, int),
			  int (*writeit) (char *, char *, int));

	      This routine initializes the XDR stream  object  pointed	to  by
	      xdrs.   The  streams  data is written to a buffer of size send
	      size; a value of zero indicates the system should use a suitable
	      default.	 The streams data is read from a buffer of size recv
	      size; it too can be set to a suitable default by passing a  zero
	      value.   When  a	streams  output  buffer  is  full, writeit is
	      called.  Similarly, when a streams input buffer is empty,  rea
	      dit is called.  The behavior of these two routines is similar to
	      the system calls read(2) and write(2),  except  that  handle  is
	      passed  to the former routines as the first argument.  Note: the
	      XDR streams op field must be set by the caller.

	      Warning: this  XDR  stream  implements  an  intermediate	record
	      stream.	Therefore  there are additional bytes in the stream to
	      provide record boundary information.

       bool_t xdrrec_endofrecord(XDR *xdrs, int sendnow);

	      This routine can be invoked only	on  streams  created  by  xdr
	      rec_create().  The data in the output buffer is marked as a com
	      pleted record, and the output buffer is optionally  written  out
	      if  sendnow  is  non-zero.   This routine returns one if it suc
	      ceeds, zero otherwise.

       bool_t xdrrec_eof(XDR *xdrs);

	      This routine can be invoked only	on  streams  created  by  xdr
	      rec_create().  After consuming the rest of the current record in
	      the stream, this routine returns one if the stream has  no  more
	      input, zero otherwise.

       bool_t xdrrec_skiprecord(XDR *xdrs);

	      This  routine  can  be  invoked  only on streams created by xdr
	      rec_create().  It tells the XDR implementation that the rest  of
	      the  current  record in the streams input buffer should be dis
	      carded.  This routine returns one if it  succeeds,  zero	other
	      wise.

       bool_t xdr_reference(XDR *xdrs, char **pp, unsigned int size,
			    xdrproc_t proc);

	      A  primitive  that  provides  pointer chasing within structures.
	      The argument pp is the address  of  the  pointer;  size  is  the
	      sizeof  the  structure  that  *pp  points to; and proc is an XDR
	      procedure that filters the structure between its C form and  its
	      external	representation.   This	routine returns one if it suc
	      ceeds, zero otherwise.

	      Warning: this routine does not understand  NULL  pointers.   Use
	      xdr_pointer() instead.

       xdr_setpos(XDR *xdrs, unsigned int pos);

	      A  macro	that  invokes the set position routine associated with
	      the XDR stream xdrs.  The  argument  pos	is  a  position  value
	      obtained from xdr_getpos().  This routine returns one if the XDR
	      stream could be repositioned, and zero otherwise.

	      Warning: it  is  difficult  to  reposition  some	types  of  XDR
	      streams,	so  this  routine may fail with one type of stream and
	      succeed with another.

       bool_t xdr_short(XDR *xdrs, short *sp);

	      A filter primitive that translates between C short integers  and
	      their  external representations.	This routine returns one if it
	      succeeds, zero otherwise.

       void xdrstdio_create(XDR *xdrs, FILE *file, enum xdr_op op);

	      This routine initializes the XDR stream  object  pointed	to  by
	      xdrs.   The  XDR	stream	data  is written to, or read from, the
	      stdio stream file.  The argument op determines the direction  of
	      the XDR stream (either XDR_ENCODE, XDR_DECODE, or XDR_FREE).

	      Warning:	the  destroy  routine associated with such XDR streams
	      calls fflush(3) on the file stream, but never fclose(3).

       bool_t xdr_string(XDR *xdrs, char **sp, unsigned int maxsize);

	      A filter primitive that translates between C strings  and  their
	      corresponding   external	representations.   Strings  cannot  be
	      longer than maxsize.  Note: sp is the address  of  the  strings
	      pointer.	 This  routine returns one if it succeeds, zero other
	      wise.

       bool_t xdr_u_char(XDR *xdrs, unsigned char *ucp);

	      A filter primitive that translates between unsigned C characters
	      and their external representations.  This routine returns one if
	      it succeeds, zero otherwise.

       bool_t xdr_u_int(XDR *xdrs, unsigned *up);

	      A filter primitive that translates between C  unsigned  integers
	      and their external representations.  This routine returns one if
	      it succeeds, zero otherwise.

       bool_t xdr_u_long(XDR *xdrs, unsigned long *ulp);

	      A filter primitive that translates between C unsigned long inte
	      gers  and  their external representations.  This routine returns
	      one if it succeeds, zero otherwise.

       bool_t xdr_u_short(XDR *xdrs, unsigned short *usp);

	      A filter primitive that  translates  between  C  unsigned  short
	      integers	and  their  external  representations.	 This  routine
	      returns one if it succeeds, zero otherwise.

       bool_t xdr_union(XDR *xdrs, int *dscmp, char *unp,
			struct xdr_discrim *choices,
			xdrproc_t defaultarm);	   /* may equal NULL */

	      A filter primitive that translates  between  a  discriminated  C
	      union  and  its corresponding external representation.  It first
	      translates the discriminant of the union located at dscmp.  This
	      discriminant is always an enum_t.  Next the union located at unp
	      is translated.  The argument choices is a pointer to an array of
	      xdr_discrim()  structures.   Each  structure contains an ordered
	      pair of [value,proc].  If the unions discriminant is  equal  to
	      the  associated  value, then the proc is called to translate the
	      union.  The end of the xdr_discrim() structure array is  denoted
	      by a routine of value NULL.  If the discriminant is not found in
	      the choices array, then the defaultarm procedure is  called  (if
	      it is not NULL).	Returns one if it succeeds, zero otherwise.

       bool_t xdr_vector(XDR *xdrs, char *arrp, unsigned int size,
			 unsigned int elsize, xdrproc_t elproc);

	      A  filter  primitive that translates between fixed-length arrays
	      and their corresponding external representations.  The  argument
	      arrp  is	the address of the pointer to the array, while size is
	      the element count of the array.	The  argument  elsize  is  the
	      sizeof each of the arrays elements, and elproc is an XDR filter
	      that translates between the array elements C  form,  and	their
	      external	representation.   This	routine returns one if it suc
	      ceeds, zero otherwise.

       bool_t xdr_void(void);

	      This routine always returns one.	It may be passed to  RPC  rou
	      tines  that  require a function argument, where nothing is to be
	      done.

       bool_t xdr_wrapstring(XDR *xdrs, char **sp);

	      A primitive that	calls  xdr_string(xdrs,  sp,MAXUN.UNSIGNED  );
	      where  MAXUN.UNSIGNED  is the maximum value of an unsigned inte
	      ger.  xdr_wrapstring() is handy because the RPC package passes a
	      maximum  of two XDR routines as arguments, and xdr_string(), one
	      of the most frequently used primitives, requires three.  Returns
	      one if it succeeds, zero otherwise.

SEE ALSO
       rpc(3)

       The following manuals:
	      eXternal Data Representation Standard: Protocol Specification
	      eXternal Data Representation: Sun Technical Notes
	      XDR:   External  Data  Representation  Standard,	RFC 1014,  Sun
	      Microsystems, Inc., USC-ISI.

COLOPHON
       This page is part of release 3.05 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



				  2007-12-30				XDR(3)




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