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XDR(3)			   Linux Programmer's 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 <rpc/xdr.h> 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 <rpc/xdr.h>.

       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 array's 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 inline routine associated with the XDR
	      stream, xdrs.  The routine returns a  pointer  to	 a  contiguous
	      piece  of	 the  stream's	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 stream's 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  stream's  data is written to a buffer of size send-
	      size; a value of zero indicates the system should use a suitable
	      default.	 The stream's 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	stream's  output  buffer  is  full, writeit is
	      called.  Similarly, when a stream's 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 stream's op field must be set by the caller.

	      Warning: To read from an XDR stream created by this API,	you'll
	      need to call xdrrec_skiprecord(3) first before calling any other
	      XDR APIs.	 This inserts additional bytes in the stream  to  pro-
	      vide  record  boundary  information.   Also, XDR streams created
	      with different xdr*_create APIs are not compatible for the  same
	      reason.

       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 nonzero.  This routine returns one if it succeeds,
	      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 stream's 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 pro-
	      cedure  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 string's
	      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 union's 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 array's 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.

ATTRIBUTES
       For  an	explanation  of	 the  terms  used   in	 this	section,   see
       attributes(7).

       +--------------------------------+---------------+---------+
       |Interface			| Attribute	| Value	  |
       +--------------------------------+---------------+---------+
       |xdr_array(), xdr_bool(),	| Thread safety | MT-Safe |
       |xdr_bytes(), xdr_char(),	|		|	  |
       |xdr_destroy(), xdr_double(),	|		|	  |
       |xdr_enum(), xdr_float(),	|		|	  |
       |xdr_free(), xdr_getpos(),	|		|	  |
       |xdr_inline(), xdr_int(),	|		|	  |
       |xdr_long(), xdrmem_create(),	|		|	  |
       |xdr_opaque(), xdr_pointer(),	|		|	  |
       |xdrrec_create(), xdrrec_eof(),	|		|	  |
       |xdrrec_endofrecord(),		|		|	  |
       |xdrrec_skiprecord(),		|		|	  |
       |xdr_reference(), xdr_setpos(),	|		|	  |
       |xdr_short(), xdrstdio_create(), |		|	  |
       |xdr_string(), xdr_u_char(),	|		|	  |
       |xdr_u_int(), xdr_u_long(),	|		|	  |
       |xdr_u_short(), xdr_union(),	|		|	  |
       |xdr_vector(), xdr_void(),	|		|	  |
       |xdr_wrapstring()		|		|	  |
       +--------------------------------+---------------+---------+

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
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       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.



				  2015-07-23				XDR(3)