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NAME

       xdr - library routines for external data representation

SYNOPSIS AND DESCRIPTION

       These   routines   allow  C  programmers  to  describe  arbitrary  data
       structures 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_ti) (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
              succeeds, 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
              invoking 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
              succeeds, 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
              desirable feature of XDR streams is that simple arithmetic works
              with this number, although the XDR  stream  instances  need  not
              guarantee 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
              succeeds, 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
              represent  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
              sendsize; a value of zero indicates  the  system  should  use  a
              suitable  default.   The  stream's data is read from a buffer of
              size recvsize; 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,  readit 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: 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
              xdrrec_create().   The  data in the output buffer is marked as a
              completed 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
              xdrrec_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
              xdrrec_create().  It tells the XDR implementation that the  rest
              of  the  current  record  in the stream's input buffer should be
              discarded.  This  routine  returns  one  if  it  succeeds,  zero
              otherwise.

       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
              succeeds, 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
              otherwise.

       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
              integers  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
              succeeds, zero otherwise.

       bool_t xdr_void(void);

              This routine always returns  one.   It  may  be  passed  to  RPC
              routines  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
              integer.  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 3.65 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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