man3/getprotoent_r.3

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  26 .TH GETPROTOENT_R 3  2019-03-06 "GNU" "Linux Programmer's Manual"
  27 .SH NAME
  28 getprotoent_r, getprotobyname_r, getprotobynumber_r \- get
  29 protocol entry (reentrant)
  30 .SH SYNOPSIS
  31 .nf
  32 .B #include <netdb.h>
  33 .PP
  34 .BI "int getprotoent_r(struct protoent *" result_buf ", char *" buf ,
  35 .BI "                size_t " buflen ", struct protoent **" result );
  36 .PP
  37 .BI "int getprotobyname_r(const char *" name ,
  38 .BI "                struct protoent *" result_buf ", char *" buf ,
  39 .BI "                size_t " buflen ", struct protoent **" result );
  40 .PP
  41 .BI "int getprotobynumber_r(int " proto ,
  42 .BI "                struct protoent *" result_buf ", char *" buf ,
  43 .BI "                size_t " buflen ", struct protoent **" result );
  44 .PP
  45 .fi
  46 .in -4n
  47 Feature Test Macro Requirements for glibc (see
  48 .BR feature_test_macros (7)):
  49 .ad l
  50 .in
  51 .PP
  52 .BR getprotoent_r (),
  53 .BR getprotobyname_r (),
  54 .BR getprotobynumber_r ():
  55     Since glibc 2.19:
  56         _DEFAULT_SOURCE
  57     Glibc 2.19 and earlier:
  58         _BSD_SOURCE || _SVID_SOURCE
  59 .ad b
  60 .SH DESCRIPTION
  61 The
  62 .BR getprotoent_r (),
  63 .BR getprotobyname_r (),
  64 and
  65 .BR getprotobynumber_r ()
  66 functions are the reentrant equivalents of, respectively,
  67 .BR getprotoent (3),
  68 .BR getprotobyname (3),
  69 and
  70 .BR getprotobynumber (3).
  71 They differ in the way that the
  72 .I protoent
  73 structure is returned,
  74 and in the function calling signature and return value.
  75 This manual page describes just the differences from
  76 the nonreentrant functions.
  77 .PP
  78 Instead of returning a pointer to a statically allocated
  79 .I protoent
  80 structure as the function result,
  81 these functions copy the structure into the location pointed to by
  82 .IR result_buf .
  83 .PP
  84 The
  85 .I buf
  86 array is used to store the string fields pointed to by the returned
  87 .I protoent
  88 structure.
  89 (The nonreentrant functions allocate these strings in static storage.)
  90 The size of this array is specified in
  91 .IR buflen .
  92 If
  93 .I buf
  94 is too small, the call fails with the error
  95 .BR ERANGE ,
  96 and the caller must try again with a larger buffer.
  97 (A buffer of length 1024 bytes should be sufficient for most applications.)
  98 .\" I can find no information on the required/recommended buffer size;
  99 .\" the nonreentrant functions use a 1024 byte buffer.
 100 .\" The 1024 byte value is also what the Solaris man page suggests. -- mtk
 101 .PP
 102 If the function call successfully obtains a protocol record, then
 103 .I *result
 104 is set pointing to
 105 .IR result_buf ;
 106 otherwise,
 107 .I *result
 108 is set to NULL.
 109 .SH RETURN VALUE
 110 On success, these functions return 0.
 111 On error, they return one of the positive error numbers listed in ERRORS.
 112 .PP
 113 On error, record not found
 114 .RB ( getprotobyname_r (),
 115 .BR getprotobynumber_r ()),
 116 or end of input
 117 .RB ( getprotoent_r ())
 118 .I result
 119 is set to NULL.
 120 .SH ERRORS
 121 .TP
 122 .B ENOENT
 123 .RB ( getprotoent_r ())
 124 No more records in database.
 125 .TP
 126 .B ERANGE
 127 .I buf
 128 is too small.
 129 Try again with a larger buffer
 130 (and increased
 131 .IR buflen ).
 132 .SH ATTRIBUTES
 133 For an explanation of the terms used in this section, see
 134 .BR attributes (7).
 135 .TS
 136 allbox;
 137 lbw20 lb lb
 138 l l l.
 139 Interface       Attribute       Value
 140 T{
 141 .BR getprotoent_r (),
 142 .br
 143 .BR getprotobyname_r (),
 144 .br
 145 .BR getprotobynumber_r ()
 146 T}      Thread safety   MT-Safe locale
 147 .TE
 148 .sp 1
 149 .SH CONFORMING TO
 150 These functions are GNU extensions.
 151 Functions with similar names exist on some other systems,
 152 though typically with different calling signatures.
 153 .SH EXAMPLE
 154 The program below uses
 155 .BR getprotobyname_r ()
 156 to retrieve the protocol record for the protocol named
 157 in its first command-line argument.
 158 If a second (integer) command-line argument is supplied,
 159 it is used as the initial value for
 160 .IR buflen ;
 161 if
 162 .BR getprotobyname_r ()
 163 fails with the error
 164 .BR ERANGE ,
 165 the program retries with larger buffer sizes.
 166 The following shell session shows a couple of sample runs:
 167 .PP
 168 .in +4n
 169 .EX
 170 .RB "$" " ./a.out tcp 1"
 171 ERANGE! Retrying with larger buffer
 172 getprotobyname_r() returned: 0 (success)  (buflen=78)
 173 p_name=tcp; p_proto=6; aliases=TCP
 174 .RB "$" " ./a.out xxx 1"
 175 ERANGE! Retrying with larger buffer
 176 getprotobyname_r() returned: 0 (success)  (buflen=100)
 177 Call failed/record not found
 178 .EE
 179 .in
 180 .SS Program source
 181 \&
 182 .EX
 183 #define _GNU_SOURCE
 184 #include <ctype.h>
 185 #include <netdb.h>
 186 #include <stdlib.h>
 187 #include <stdio.h>
 188 #include <errno.h>
 189 #include <string.h>
 190
 191 #define MAX_BUF 10000
 192
 193 int
 194 main(int argc, char *argv[])
 195 {
 196     int buflen, erange_cnt, s;
 197     struct protoent result_buf;
 198     struct protoent *result;
 199     char buf[MAX_BUF];
 200     char **p;
 201
 202     if (argc < 2) {
 203         printf("Usage: %s proto\-name [buflen]\en", argv[0]);
 204         exit(EXIT_FAILURE);
 205     }
 206
 207     buflen = 1024;
 208     if (argc > 2)
 209         buflen = atoi(argv[2]);
 210
 211     if (buflen > MAX_BUF) {
 212         printf("Exceeded buffer limit (%d)\en", MAX_BUF);
 213         exit(EXIT_FAILURE);
 214     }
 215
 216     erange_cnt = 0;
 217     do {
 218         s = getprotobyname_r(argv[1], &result_buf,
 219                      buf, buflen, &result);
 220         if (s == ERANGE) {
 221             if (erange_cnt == 0)
 222                 printf("ERANGE! Retrying with larger buffer\en");
 223             erange_cnt++;
 224
 225             /* Increment a byte at a time so we can see exactly
 226                what size buffer was required */
 227
 228             buflen++;
 229
 230             if (buflen > MAX_BUF) {
 231                 printf("Exceeded buffer limit (%d)\en", MAX_BUF);
 232                 exit(EXIT_FAILURE);
 233             }
 234         }
 235     } while (s == ERANGE);
 236
 237     printf("getprotobyname_r() returned: %s  (buflen=%d)\en",
 238             (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
 239             strerror(s), buflen);
 240
 241     if (s != 0 || result == NULL) {
 242         printf("Call failed/record not found\en");
 243         exit(EXIT_FAILURE);
 244     }
 245
 246     printf("p_name=%s; p_proto=%d; aliases=",
 247                 result_buf.p_name, result_buf.p_proto);
 248     for (p = result_buf.p_aliases; *p != NULL; p++)
 249         printf("%s ", *p);
 250     printf("\en");
 251
 252     exit(EXIT_SUCCESS);
 253 }
 254 .EE
 255 .SH SEE ALSO
 256 .BR getprotoent (3),
 257 .BR protocols (5)