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NAME | SYNOPSIS AND DESCRIPTION | ATTRIBUTES | SEE ALSO | COLOPHON |
XDR(3) Linux Programmer's Manual XDR(3)
xdr - library routines for external data representation
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_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 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: to read from an XDR stream created by this API,
you'll need to call xdrrec_skiprecord() first before calling
any other XDR APIs. This inserts additional bytes in the
stream to provide 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
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.
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() │ │ │
└────────────────────────────────┴───────────────┴─────────┘
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.
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2015-07-23 XDR(3)
Pages that refer to this page: rpc(3)