man3/getprotoent_r.3

   1 '\" t
   2 .\" Copyright 2008, Linux Foundation, written by Michael Kerrisk
   3 .\"     <mtk.manpages@gmail.com>
   4 .\"
   5 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   6 .\"
   7 .TH getprotoent_r 3 (date) "Linux man-pages (unreleased)"
   8 .SH NAME
   9 getprotoent_r, getprotobyname_r, getprotobynumber_r \- get
  10 protocol entry (reentrant)
  11 .SH LIBRARY
  12 Standard C library
  13 .RI ( libc ", " \-lc )
  14 .SH SYNOPSIS
  15 .nf
  16 .B #include <netdb.h>
  17 .PP
  18 .BI "int getprotoent_r(struct protoent *restrict " result_buf ,
  19 .BI "                  char " buf "[restrict ." buflen "], size_t " buflen ,
  20 .BI "                  struct protoent **restrict " result );
  21 .BI "int getprotobyname_r(const char *restrict " name ,
  22 .BI "                  struct protoent *restrict " result_buf ,
  23 .BI "                  char " buf "[restrict ." buflen "], size_t " buflen ,
  24 .BI "                  struct protoent **restrict " result );
  25 .BI "int getprotobynumber_r(int " proto ,
  26 .BI "                  struct protoent *restrict " result_buf ,
  27 .BI "                  char " buf "[restrict ." buflen "], size_t " buflen ,
  28 .BI "                  struct protoent **restrict " result );
  29 .PP
  30 .fi
  31 .RS -4
  32 Feature Test Macro Requirements for glibc (see
  33 .BR feature_test_macros (7)):
  34 .RE
  35 .PP
  36 .BR getprotoent_r (),
  37 .BR getprotobyname_r (),
  38 .BR getprotobynumber_r ():
  39 .nf
  40     Since glibc 2.19:
  41         _DEFAULT_SOURCE
  42     glibc 2.19 and earlier:
  43         _BSD_SOURCE || _SVID_SOURCE
  44 .fi
  45 .SH DESCRIPTION
  46 The
  47 .BR getprotoent_r (),
  48 .BR getprotobyname_r (),
  49 and
  50 .BR getprotobynumber_r ()
  51 functions are the reentrant equivalents of, respectively,
  52 .BR getprotoent (3),
  53 .BR getprotobyname (3),
  54 and
  55 .BR getprotobynumber (3).
  56 They differ in the way that the
  57 .I protoent
  58 structure is returned,
  59 and in the function calling signature and return value.
  60 This manual page describes just the differences from
  61 the nonreentrant functions.
  62 .PP
  63 Instead of returning a pointer to a statically allocated
  64 .I protoent
  65 structure as the function result,
  66 these functions copy the structure into the location pointed to by
  67 .IR result_buf .
  68 .PP
  69 The
  70 .I buf
  71 array is used to store the string fields pointed to by the returned
  72 .I protoent
  73 structure.
  74 (The nonreentrant functions allocate these strings in static storage.)
  75 The size of this array is specified in
  76 .IR buflen .
  77 If
  78 .I buf
  79 is too small, the call fails with the error
  80 .BR ERANGE ,
  81 and the caller must try again with a larger buffer.
  82 (A buffer of length 1024 bytes should be sufficient for most applications.)
  83 .\" I can find no information on the required/recommended buffer size;
  84 .\" the nonreentrant functions use a 1024 byte buffer.
  85 .\" The 1024 byte value is also what the Solaris man page suggests. -- mtk
  86 .PP
  87 If the function call successfully obtains a protocol record, then
  88 .I *result
  89 is set pointing to
  90 .IR result_buf ;
  91 otherwise,
  92 .I *result
  93 is set to NULL.
  94 .SH RETURN VALUE
  95 On success, these functions return 0.
  96 On error, they return one of the positive error numbers listed in ERRORS.
  97 .PP
  98 On error, record not found
  99 .RB ( getprotobyname_r (),
 100 .BR getprotobynumber_r ()),
 101 or end of input
 102 .RB ( getprotoent_r ())
 103 .I result
 104 is set to NULL.
 105 .SH ERRORS
 106 .TP
 107 .B ENOENT
 108 .RB ( getprotoent_r ())
 109 No more records in database.
 110 .TP
 111 .B ERANGE
 112 .I buf
 113 is too small.
 114 Try again with a larger buffer
 115 (and increased
 116 .IR buflen ).
 117 .SH ATTRIBUTES
 118 For an explanation of the terms used in this section, see
 119 .BR attributes (7).
 120 .ad l
 121 .nh
 122 .TS
 123 allbox;
 124 lbx lb lb
 125 l l l.
 126 Interface       Attribute       Value
 127 T{
 128 .BR getprotoent_r (),
 129 .BR getprotobyname_r (),
 130 .BR getprotobynumber_r ()
 131 T}      Thread safety   MT-Safe locale
 132 .TE
 133 .hy
 134 .ad
 135 .sp 1
 136 .SH VERSIONS
 137 Functions with similar names exist on some other systems,
 138 though typically with different calling signatures.
 139 .SH STANDARDS
 140 GNU.
 141 .SH EXAMPLES
 142 The program below uses
 143 .BR getprotobyname_r ()
 144 to retrieve the protocol record for the protocol named
 145 in its first command-line argument.
 146 If a second (integer) command-line argument is supplied,
 147 it is used as the initial value for
 148 .IR buflen ;
 149 if
 150 .BR getprotobyname_r ()
 151 fails with the error
 152 .BR ERANGE ,
 153 the program retries with larger buffer sizes.
 154 The following shell session shows a couple of sample runs:
 155 .PP
 156 .in +4n
 157 .EX
 158 .RB "$" " ./a.out tcp 1"
 159 ERANGE! Retrying with larger buffer
 160 getprotobyname_r() returned: 0 (success)  (buflen=78)
 161 p_name=tcp; p_proto=6; aliases=TCP
 162 .RB "$" " ./a.out xxx 1"
 163 ERANGE! Retrying with larger buffer
 164 getprotobyname_r() returned: 0 (success)  (buflen=100)
 165 Call failed/record not found
 166 .EE
 167 .in
 168 .SS Program source
 169 \&
 170 .\" SRC BEGIN (getprotoent_r.c)
 171 .EX
 172 #define _GNU_SOURCE
 173 #include <ctype.h>
 174 #include <errno.h>
 175 #include <netdb.h>
 176 #include <stdio.h>
 177 #include <stdlib.h>
 178 #include <string.h>
 179 \&
 180 #define MAX_BUF 10000
 181 \&
 182 int
 183 main(int argc, char *argv[])
 184 {
 185     int buflen, erange_cnt, s;
 186     struct protoent result_buf;
 187     struct protoent *result;
 188     char buf[MAX_BUF];
 189 \&
 190     if (argc < 2) {
 191         printf("Usage: %s proto\-name [buflen]\en", argv[0]);
 192         exit(EXIT_FAILURE);
 193     }
 194 \&
 195     buflen = 1024;
 196     if (argc > 2)
 197         buflen = atoi(argv[2]);
 198 \&
 199     if (buflen > MAX_BUF) {
 200         printf("Exceeded buffer limit (%d)\en", MAX_BUF);
 201         exit(EXIT_FAILURE);
 202     }
 203 \&
 204     erange_cnt = 0;
 205     do {
 206         s = getprotobyname_r(argv[1], &result_buf,
 207                              buf, buflen, &result);
 208         if (s == ERANGE) {
 209             if (erange_cnt == 0)
 210                 printf("ERANGE! Retrying with larger buffer\en");
 211             erange_cnt++;
 212 \&
 213             /* Increment a byte at a time so we can see exactly
 214                what size buffer was required. */
 215 \&
 216             buflen++;
 217 \&
 218             if (buflen > MAX_BUF) {
 219                 printf("Exceeded buffer limit (%d)\en", MAX_BUF);
 220                 exit(EXIT_FAILURE);
 221             }
 222         }
 223     } while (s == ERANGE);
 224 \&
 225     printf("getprotobyname_r() returned: %s  (buflen=%d)\en",
 226            (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
 227            strerror(s), buflen);
 228 \&
 229     if (s != 0 || result == NULL) {
 230         printf("Call failed/record not found\en");
 231         exit(EXIT_FAILURE);
 232     }
 233 \&
 234     printf("p_name=%s; p_proto=%d; aliases=",
 235            result_buf.p_name, result_buf.p_proto);
 236     for (char **p = result_buf.p_aliases; *p != NULL; p++)
 237         printf("%s ", *p);
 238     printf("\en");
 239 \&
 240     exit(EXIT_SUCCESS);
 241 }
 242 .EE
 243 .\" SRC END
 244 .SH SEE ALSO
 245 .BR getprotoent (3),
 246 .BR protocols (5)