1XDR(3) Linux Programmer's Manual XDR(3)
2
6 xdr - library routines for external data representation
7
9 These routines allow C programmers to describe arbitrary data struc‐
10 tures in a machine-independent fashion. Data for remote procedure
11 calls are transmitted using these routines.
12 The prototypes below are declared in <rpc/xdr.h> and make use of the
14 following types:
15 typedef int bool_t;
17 typedef bool_t (*xdrproc_ti) (XDR *, void *,...);
19 For the declaration of the XDR type, see <rpc/xdr.h>.
21 bool_t xdr_array(XDR *xdrs, char **arrp, unsigned int *sizep,
23 unsigned int maxsize, unsigned int elsize,
24 xdrproc_t elproc);
25 A filter primitive that translates between variable-length
27 arrays and their corresponding external representations. The
28 argument arrp is the address of the pointer to the array, while
29 sizep is the address of the element count of the array; this
30 element count cannot exceed maxsize. The argument elsize is the
31 sizeof each of the array's elements, and elproc is an XDR filter
32 that translates between the array elements' C form, and their
33 external representation. This routine returns one if it suc‐
34 ceeds, zero otherwise.
35 bool_t xdr_bool(XDR *xdrs, bool_t *bp);
37 A filter primitive that translates between booleans (C integers)
39 and their external representations. When encoding data, this
40 filter produces values of either one or zero. This routine
41 returns one if it succeeds, zero otherwise.
42 bool_t xdr_bytes(XDR *xdrs, char **sp, unsigned int *sizep,
44 unsigned int maxsize);
45 A filter primitive that translates between counted byte strings
47 and their external representations. The argument sp is the
48 address of the string pointer. The length of the string is
49 located at address sizep; strings cannot be longer than maxsize.
50 This routine returns one if it succeeds, zero otherwise.
51 bool_t xdr_char(XDR *xdrs, char *cp);
53 A filter primitive that translates between C characters and
55 their external representations. This routine returns one if it
56 succeeds, zero otherwise. Note: encoded characters are not
57 packed, and occupy 4 bytes each. For arrays of characters, it
58 is worthwhile to consider xdr_bytes(), xdr_opaque() or
59 xdr_string().
60 void xdr_destroy(XDR *xdrs);
62 A macro that invokes the destroy routine associated with the XDR
64 stream, xdrs. Destruction usually involves freeing private data
65 structures associated with the stream. Using xdrs after invok‐
66 ing xdr_destroy() is undefined.
67 bool_t xdr_double(XDR *xdrs, double *dp);
69 A filter primitive that translates between C double precision
71 numbers and their external representations. This routine
72 returns one if it succeeds, zero otherwise.
73 bool_t xdr_enum(XDR *xdrs, enum_t *ep);
75 A filter primitive that translates between C enums (actually
77 integers) and their external representations. This routine
78 returns one if it succeeds, zero otherwise.
79 bool_t xdr_float(XDR *xdrs, float *fp);
81 A filter primitive that translates between C floats and their
83 external representations. This routine returns one if it suc‐
84 ceeds, zero otherwise.
85 void xdr_free(xdrproc_t proc, char *objp);
87 Generic freeing routine. The first argument is the XDR routine
89 for the object being freed. The second argument is a pointer to
90 the object itself. Note: the pointer passed to this routine is
91 not freed, but what it points to is freed (recursively).
92 unsigned int xdr_getpos(XDR *xdrs);
94 A macro that invokes the get-position routine associated with
96 the XDR stream, xdrs. The routine returns an unsigned integer,
97 which indicates the position of the XDR byte stream. A desir‐
98 able feature of XDR streams is that simple arithmetic works with
99 this number, although the XDR stream instances need not guaran‐
100 tee this.
101 long *xdr_inline(XDR *xdrs, int len);
103 A macro that invokes the inline routine associated with the XDR
105 stream, xdrs. The routine returns a pointer to a contiguous
106 piece of the stream's buffer; len is the byte length of the
107 desired buffer. Note: pointer is cast to long *.
108 Warning: xdr_inline() may return NULL (0) if it cannot allocate
110 a contiguous piece of a buffer. Therefore the behavior may vary
111 among stream instances; it exists for the sake of efficiency.
112 bool_t xdr_int(XDR *xdrs, int *ip);
114 A filter primitive that translates between C integers and their
116 external representations. This routine returns one if it suc‐
117 ceeds, zero otherwise.
118 bool_t xdr_long(XDR *xdrs, long *lp);
120 A filter primitive that translates between C long integers and
122 their external representations. This routine returns one if it
123 succeeds, zero otherwise.
124 void xdrmem_create(XDR *xdrs, char *addr, unsigned int size,
126 enum xdr_op op);
127 This routine initializes the XDR stream object pointed to by
129 xdrs. The stream's data is written to, or read from, a chunk of
130 memory at location addr whose length is no more than size bytes
131 long. The op determines the direction of the XDR stream (either
132 XDR_ENCODE, XDR_DECODE, or XDR_FREE).
133 bool_t xdr_opaque(XDR *xdrs, char *cp, unsigned int cnt);
135 A filter primitive that translates between fixed size opaque
137 data and its external representation. The argument cp is the
138 address of the opaque object, and cnt is its size in bytes.
139 This routine returns one if it succeeds, zero otherwise.
140 bool_t xdr_pointer(XDR *xdrs, char **objpp,
142 unsigned int objsize, xdrproc_t xdrobj);
143 Like xdr_reference() except that it serializes NULL pointers,
145 whereas xdr_reference() does not. Thus, xdr_pointer() can rep‐
146 resent recursive data structures, such as binary trees or linked
147 lists.
148 void xdrrec_create(XDR *xdrs, unsigned int sendsize,
150 unsigned int recvsize, char *handle,
151 int (*readit) (char *, char *, int),
152 int (*writeit) (char *, char *, int));
153 This routine initializes the XDR stream object pointed to by
155 xdrs. The stream's data is written to a buffer of size send‐
156 size; a value of zero indicates the system should use a suitable
157 default. The stream's data is read from a buffer of size recv‐
158 size; it too can be set to a suitable default by passing a zero
159 value. When a stream's output buffer is full, writeit is
160 called. Similarly, when a stream's input buffer is empty, rea‐
161 dit is called. The behavior of these two routines is similar to
162 the system calls read(2) and write(2), except that handle is
163 passed to the former routines as the first argument. Note: the
164 XDR stream's op field must be set by the caller.
165 Warning: this XDR stream implements an intermediate record
167 stream. Therefore there are additional bytes in the stream to
168 provide record boundary information.
169 bool_t xdrrec_endofrecord(XDR *xdrs, int sendnow);
171 This routine can be invoked only on streams created by xdr‐
173 rec_create(). The data in the output buffer is marked as a com‐
174 pleted record, and the output buffer is optionally written out
175 if sendnow is nonzero. This routine returns one if it succeeds,
176 zero otherwise.
177 bool_t xdrrec_eof(XDR *xdrs);
179 This routine can be invoked only on streams created by xdr‐
181 rec_create(). After consuming the rest of the current record in
182 the stream, this routine returns one if the stream has no more
183 input, zero otherwise.
184 bool_t xdrrec_skiprecord(XDR *xdrs);
186 This routine can be invoked only on streams created by xdr‐
188 rec_create(). It tells the XDR implementation that the rest of
189 the current record in the stream's input buffer should be dis‐
190 carded. This routine returns one if it succeeds, zero other‐
191 wise.
192 bool_t xdr_reference(XDR *xdrs, char **pp, unsigned int size,
194 xdrproc_t proc);
195 A primitive that provides pointer chasing within structures.
197 The argument pp is the address of the pointer; size is the
198 sizeof the structure that *pp points to; and proc is an XDR pro‐
199 cedure that filters the structure between its C form and its
200 external representation. This routine returns one if it suc‐
201 ceeds, zero otherwise.
202 Warning: this routine does not understand NULL pointers. Use
204 xdr_pointer() instead.
205 xdr_setpos(XDR *xdrs, unsigned int pos);
207 A macro that invokes the set position routine associated with
209 the XDR stream xdrs. The argument pos is a position value
210 obtained from xdr_getpos(). This routine returns one if the XDR
211 stream could be repositioned, and zero otherwise.
212 Warning: it is difficult to reposition some types of XDR
214 streams, so this routine may fail with one type of stream and
215 succeed with another.
216 bool_t xdr_short(XDR *xdrs, short *sp);
218 A filter primitive that translates between C short integers and
220 their external representations. This routine returns one if it
221 succeeds, zero otherwise.
222 void xdrstdio_create(XDR *xdrs, FILE *file, enum xdr_op op);
224 This routine initializes the XDR stream object pointed to by
226 xdrs. The XDR stream data is written to, or read from, the
227 stdio stream file. The argument op determines the direction of
228 the XDR stream (either XDR_ENCODE, XDR_DECODE, or XDR_FREE).
229 Warning: the destroy routine associated with such XDR streams
231 calls fflush(3) on the file stream, but never fclose(3).
232 bool_t xdr_string(XDR *xdrs, char **sp, unsigned int maxsize);
234 A filter primitive that translates between C strings and their
236 corresponding external representations. Strings cannot be
237 longer than maxsize. Note: sp is the address of the string's
238 pointer. This routine returns one if it succeeds, zero other‐
239 wise.
240 bool_t xdr_u_char(XDR *xdrs, unsigned char *ucp);
242 A filter primitive that translates between unsigned C characters
244 and their external representations. This routine returns one if
245 it succeeds, zero otherwise.
246 bool_t xdr_u_int(XDR *xdrs, unsigned *up);
248 A filter primitive that translates between C unsigned integers
250 and their external representations. This routine returns one if
251 it succeeds, zero otherwise.
252 bool_t xdr_u_long(XDR *xdrs, unsigned long *ulp);
254 A filter primitive that translates between C unsigned long inte‐
256 gers and their external representations. This routine returns
257 one if it succeeds, zero otherwise.
258 bool_t xdr_u_short(XDR *xdrs, unsigned short *usp);
260 A filter primitive that translates between C unsigned short
262 integers and their external representations. This routine
263 returns one if it succeeds, zero otherwise.
264 bool_t xdr_union(XDR *xdrs, int *dscmp, char *unp,
266 struct xdr_discrim *choices,
267 xdrproc_t defaultarm); /* may equal NULL */
268 A filter primitive that translates between a discriminated C
270 union and its corresponding external representation. It first
271 translates the discriminant of the union located at dscmp. This
272 discriminant is always an enum_t. Next the union located at unp
273 is translated. The argument choices is a pointer to an array of
274 xdr_discrim() structures. Each structure contains an ordered
275 pair of [value,proc]. If the union's discriminant is equal to
276 the associated value, then the proc is called to translate the
277 union. The end of the xdr_discrim() structure array is denoted
278 by a routine of value NULL. If the discriminant is not found in
279 the choices array, then the defaultarm procedure is called (if
280 it is not NULL). Returns one if it succeeds, zero otherwise.
281 bool_t xdr_vector(XDR *xdrs, char *arrp, unsigned int size,
283 unsigned int elsize, xdrproc_t elproc);
284 A filter primitive that translates between fixed-length arrays
286 and their corresponding external representations. The argument
287 arrp is the address of the pointer to the array, while size is
288 the element count of the array. The argument elsize is the
289 sizeof each of the array's elements, and elproc is an XDR filter
290 that translates between the array elements' C form, and their
291 external representation. This routine returns one if it suc‐
292 ceeds, zero otherwise.
293 bool_t xdr_void(void);
295 This routine always returns one. It may be passed to RPC rou‐
297 tines that require a function argument, where nothing is to be
298 done.
299 bool_t xdr_wrapstring(XDR *xdrs, char **sp);
301 A primitive that calls xdr_string(xdrs, sp,MAXUN.UNSIGNED );
303 where MAXUN.UNSIGNED is the maximum value of an unsigned inte‐
304 ger. xdr_wrapstring() is handy because the RPC package passes a
305 maximum of two XDR routines as arguments, and xdr_string(), one
306 of the most frequently used primitives, requires three. Returns
307 one if it succeeds, zero otherwise.
308
310 rpc(3)
311 The following manuals:
313 eXternal Data Representation Standard: Protocol Specification
314 eXternal Data Representation: Sun Technical Notes
315 XDR: External Data Representation Standard, RFC 1014, Sun
316 Microsystems, Inc., USC-ISI.
317
319 This page is part of release 3.53 of the Linux man-pages project. A
320 description of the project, and information about reporting bugs, can
321 be found at http://www.kernel.org/doc/man-pages/.
322 2007-12-30 XDR(3)