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1 | .\" Copyright 2008, Linux Foundation, written by Michael Kerrisk |
2 | .\" <mtk.manpages@gmail.com> | |
3 | .\" | |
4 | .\" Permission is granted to make and distribute verbatim copies of this | |
5 | .\" manual provided the copyright notice and this permission notice are | |
6 | .\" preserved on all copies. | |
7 | .\" | |
8 | .\" Permission is granted to copy and distribute modified versions of this | |
9 | .\" manual under the conditions for verbatim copying, provided that the | |
10 | .\" entire resulting derived work is distributed under the terms of a | |
11 | .\" permission notice identical to this one. | |
12 | .\" | |
13 | .\" Since the Linux kernel and libraries are constantly changing, this | |
14 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
15 | .\" responsibility for errors or omissions, or for damages resulting from | |
16 | .\" the use of the information contained herein. The author(s) may not | |
17 | .\" have taken the same level of care in the production of this manual, | |
18 | .\" which is licensed free of charge, as they might when working | |
19 | .\" professionally. | |
20 | .\" | |
21 | .\" Formatted or processed versions of this manual, if unaccompanied by | |
22 | .\" the source, must acknowledge the copyright and authors of this work. | |
23 | .\" | |
24 | .TH GETSERVENT_R 3 2008-08-19 "GNU" "Linux Programmer's Manual" | |
25 | .SH NAME | |
26 | getservent_r, getservbyname_r, getservbyport_r \- get | |
27 | service entry (reentrant) | |
28 | .SH SYNOPSIS | |
29 | .nf | |
30 | .B #include <netdb.h> | |
31 | .sp | |
32 | .BI "int getservent_r(struct servent *" result_buf ", char *" buf , | |
33 | .BI " size_t " buflen ", struct servent **" result ); | |
34 | .sp | |
35 | .BI "int getservbyname_r(const char *" name ", const char *" proto , | |
36 | .BI " struct servent *" result_buf ", char *" buf , | |
37 | .BI " size_t " buflen ", struct servent **" result ); | |
38 | .sp | |
39 | .BI "int getservbyport_r(int " port ", const char *" proto , | |
40 | .BI " struct servent *" result_buf ", char *" buf , | |
41 | .BI " size_t " buflen ", struct servent **" result ); | |
42 | .sp | |
43 | .fi | |
44 | .in -4n | |
45 | Feature Test Macro Requirements for glibc (see | |
46 | .BR feature_test_macros (7)): | |
47 | .ad l | |
48 | .in | |
49 | .sp | |
50 | .BR getservent_r (), | |
51 | .BR getservbyname_r (), | |
52 | .BR getservbyport_r (): | |
53 | _BSD_SOURCE || _SVID_SOURCE | |
54 | .ad b | |
55 | .SH DESCRIPTION | |
56 | The | |
57 | .BR getservent_r (), | |
58 | .BR getservbyname_r (), | |
59 | and | |
60 | .BR getservbyport_r () | |
61 | functions are the reentrant equivalents of, respectively, | |
62 | .BR getservent (3), | |
63 | .BR getservbyname (3), | |
64 | and | |
65 | .BR getservbyport (3). | |
66 | They differ in the way that the | |
67 | .I servent | |
68 | structure is returned, | |
69 | and in the function calling signature and return value. | |
70 | This manual page describes just the differences from | |
71 | the non-reentrant functions. | |
72 | ||
73 | Instead of returning a pointer to a statically allocated | |
74 | .I servent | |
75 | structure as the function result, | |
76 | these functions copy the structure into the location pointed to by | |
77 | .IR result_buf . | |
78 | ||
79 | The | |
80 | .I buf | |
81 | array is used to store the string fields pointed to by the returned | |
82 | .I servent | |
83 | structure. | |
84 | (The non-reentrant functions allocate these strings in static storage.) | |
85 | The size of this array is specified in | |
86 | .IR buflen . | |
87 | If | |
88 | .I buf | |
89 | is too small, the call fails with the error | |
90 | .BR ERANGE , | |
91 | and the caller must try again with a larger buffer. | |
92 | (A buffer of length 1024 bytes should be sufficient for most applications.) | |
93 | .\" I can find no information on the required/recommended buffer size; | |
94 | .\" the non-reentrant functions use a 1024 byte buffer -- mtk. | |
95 | ||
96 | If the function call successfully obtains a service record, then | |
97 | .I *result | |
98 | is set pointing to | |
99 | .IR result_buf ; | |
100 | otherwise, | |
101 | .I *result | |
102 | is set to NULL. | |
103 | .SH "RETURN VALUE" | |
104 | On success, these functions return 0. | |
105 | On error, a positive error number is returned. | |
106 | ||
107 | On error, record not found | |
108 | .RB ( getservbyname_r (), | |
109 | .BR getservbyport_r ()), | |
110 | or end of input | |
111 | .RB ( getservent_r ()) | |
112 | .I result | |
113 | is set to NULL. | |
114 | .SH ERRORS | |
115 | .TP | |
116 | .B ENOENT | |
117 | .RB ( getservent_r ()) | |
118 | No more records in database. | |
119 | .TP | |
120 | .B ERANGE | |
121 | .I buf | |
122 | is too small. | |
123 | Try again with a larger buffer | |
124 | (and increased | |
125 | .IR buflen ). | |
126 | .SH "CONFORMING TO" | |
127 | These functions are GNU extensions. | |
128 | Functions with similar names exist on some other systems, | |
129 | though typically with different calling signatures. | |
130 | .SH EXAMPLE | |
131 | The program below uses | |
132 | .BR getservbyport_r () | |
133 | to retrieve the service record for the port and protocol named | |
134 | in its first command-line argument. | |
135 | If a third (integer) command-line argument is supplied, | |
136 | it is used as the initial value for | |
137 | .IR buflen ; | |
138 | if | |
139 | .BR getservbyport_r () | |
140 | fails with the error | |
141 | .BR ERANGE , | |
142 | the program retries with larger buffer sizes. | |
143 | The following shell session shows a couple of sample runs: | |
144 | .in +4n | |
145 | .nf | |
146 | ||
b43a3b30 | 147 | .RB "$" " ./a.out 7 tcp 1" |
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148 | ERANGE! Retrying with larger buffer |
149 | getservbyport_r() returned: 0 (success) (buflen=87) | |
150 | s_name=echo; s_proto=tcp; s_port=7; aliases= | |
b43a3b30 | 151 | .RB "$" " ./a.out 77777 tcp" |
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152 | getservbyport_r() returned: 0 (success) (buflen=1024) |
153 | Call failed/record not found | |
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154 | .fi |
155 | .in | |
9c330504 | 156 | .SS Program source |
d84d0300 | 157 | \& |
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158 | .nf |
159 | #define _GNU_SOURCE | |
160 | #include <ctype.h> | |
161 | #include <netdb.h> | |
162 | #include <stdlib.h> | |
163 | #include <stdio.h> | |
164 | #include <errno.h> | |
165 | #include <string.h> | |
166 | ||
167 | #define MAX_BUF 10000 | |
168 | ||
169 | int | |
170 | main(int argc, char *argv[]) | |
171 | { | |
172 | int buflen, erange_cnt, port, s; | |
173 | struct servent result_buf; | |
174 | struct servent *result; | |
175 | char buf[MAX_BUF]; | |
176 | char *protop; | |
177 | char **p; | |
178 | ||
179 | if (argc < 3) { | |
180 | printf("Usage: %s port\-num proto-name [buflen]\\n", argv[0]); | |
181 | exit(EXIT_FAILURE); | |
182 | } | |
183 | ||
184 | port = htons(atoi(argv[1])); | |
185 | protop = (strcmp(argv[2], "null") == 0 || | |
186 | strcmp(argv[2], "NULL") == 0) ? NULL : argv[2]; | |
187 | ||
188 | buflen = 1024; | |
189 | if (argc > 3) | |
190 | buflen = atoi(argv[3]); | |
191 | ||
192 | if (buflen > MAX_BUF) { | |
193 | printf("Exceeded buffer limit (%d)\\n", MAX_BUF); | |
194 | exit(EXIT_FAILURE); | |
195 | } | |
196 | ||
197 | erange_cnt = 0; | |
198 | do { | |
199 | s = getservbyport_r(port, protop, &result_buf, | |
200 | buf, buflen, &result); | |
201 | if (s == ERANGE) { | |
202 | if (erange_cnt == 0) | |
203 | printf("ERANGE! Retrying with larger buffer\\n"); | |
204 | erange_cnt++; | |
205 | ||
206 | /* Increment a byte at a time so we can see exactly | |
207 | what size buffer was required */ | |
208 | ||
209 | buflen++; | |
210 | ||
211 | if (buflen > MAX_BUF) { | |
212 | printf("Exceeded buffer limit (%d)\\n", MAX_BUF); | |
213 | exit(EXIT_FAILURE); | |
214 | } | |
215 | } | |
216 | } while (s == ERANGE); | |
217 | ||
218 | printf("getservbyport_r() returned: %s (buflen=%d)\\n", | |
219 | (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" : | |
220 | strerror(s), buflen); | |
221 | ||
222 | if (s != 0 || result == NULL) { | |
223 | printf("Call failed/record not found\\n"); | |
224 | exit(EXIT_FAILURE); | |
225 | } | |
226 | ||
227 | printf("s_name=%s; s_proto=%s; s_port=%d; aliases=", | |
228 | result_buf.s_name, result_buf.s_proto, | |
229 | ntohs(result_buf.s_port)); | |
230 | for (p = result_buf.s_aliases; *p != NULL; p++) | |
231 | printf("%s ", *p); | |
232 | printf("\\n"); | |
233 | ||
234 | exit(EXIT_SUCCESS); | |
235 | } | |
236 | .fi | |
237 | .SH "SEE ALSO" | |
238 | .BR getservent (3), | |
1280fbc6 | 239 | .BR services (5) |