| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
GETSERVENT_R(3) Linux Programmer's Manual GETSERVENT_R(3)
getservent_r, getservbyname_r, getservbyport_r - get service entry (reentrant)
#include <netdb.h>
int getservent_r(struct servent *result_buf, char *buf,
size_t buflen, struct servent **result);
int getservbyname_r(const char *name, const char *proto,
struct servent *result_buf, char *buf,
size_t buflen, struct servent **result);
int getservbyport_r(int port, const char *proto,
struct servent *result_buf, char *buf,
size_t buflen, struct servent **result);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getservent_r(), getservbyname_r(), getservbyport_r():
_BSD_SOURCE || _SVID_SOURCE
The getservent_r(), getservbyname_r(), and getservbyport_r() functions are the
reentrant equivalents of, respectively, getservent(3), getservbyname(3), and
getservbyport(3). They differ in the way that the servent structure is
returned, and in the function calling signature and return value. This manual
page describes just the differences from the nonreentrant functions.
Instead of returning a pointer to a statically allocated servent structure as
the function result, these functions copy the structure into the location
pointed to by result_buf.
The buf array is used to store the string fields pointed to by the returned
servent structure. (The nonreentrant functions allocate these strings in
static storage.) The size of this array is specified in buflen. If buf is
too small, the call fails with the error ERANGE, and the caller must try again
with a larger buffer. (A buffer of length 1024 bytes should be sufficient for
most applications.)
If the function call successfully obtains a service record, then *result is
set pointing to result_buf; otherwise, *result is set to NULL.
On success, these functions return 0. On error, they return one of the
positive error numbers listed in errors.
On error, record not found (getservbyname_r(), getservbyport_r()), or end of
input (getservent_r()) result is set to NULL.
ENOENT (getservent_r()) No more records in database.
ERANGE buf is too small. Try again with a larger buffer (and increased
buflen).
These functions are GNU extensions. Functions with similar names exist on
some other systems, though typically with different calling signatures.
The program below uses getservbyport_r() to retrieve the service record for
the port and protocol named in its first command-line argument. If a third
(integer) command-line argument is supplied, it is used as the initial value
for buflen; if getservbyport_r() fails with the error ERANGE, the program
retries with larger buffer sizes. The following shell session shows a couple
of sample runs:
$ ./a.out 7 tcp 1
ERANGE! Retrying with larger buffer
getservbyport_r() returned: 0 (success) (buflen=87)
s_name=echo; s_proto=tcp; s_port=7; aliases=
$ ./a.out 77777 tcp
getservbyport_r() returned: 0 (success) (buflen=1024)
Call failed/record not found
#define _GNU_SOURCE
#include <ctype.h>
#include <netdb.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <string.h>
#define MAX_BUF 10000
int
main(int argc, char *argv[])
{
int buflen, erange_cnt, port, s;
struct servent result_buf;
struct servent *result;
char buf[MAX_BUF];
char *protop;
char **p;
if (argc < 3) {
printf("Usage: %s port-num proto-name [buflen]\n", argv[0]);
exit(EXIT_FAILURE);
}
port = htons(atoi(argv[1]));
protop = (strcmp(argv[2], "null") == 0 ||
strcmp(argv[2], "NULL") == 0) ? NULL : argv[2];
buflen = 1024;
if (argc > 3)
buflen = atoi(argv[3]);
if (buflen > MAX_BUF) {
printf("Exceeded buffer limit (%d)\n", MAX_BUF);
exit(EXIT_FAILURE);
}
erange_cnt = 0;
do {
s = getservbyport_r(port, protop, &result_buf,
buf, buflen, &result);
if (s == ERANGE) {
if (erange_cnt == 0)
printf("ERANGE! Retrying with larger buffer\n");
erange_cnt++;
/* Increment a byte at a time so we can see exactly
what size buffer was required */
buflen++;
if (buflen > MAX_BUF) {
printf("Exceeded buffer limit (%d)\n", MAX_BUF);
exit(EXIT_FAILURE);
}
}
} while (s == ERANGE);
printf("getservbyport_r() returned: %s (buflen=%d)\n",
(s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" :
strerror(s), buflen);
if (s != 0 || result == NULL) {
printf("Call failed/record not found\n");
exit(EXIT_FAILURE);
}
printf("s_name=%s; s_proto=%s; s_port=%d; aliases=",
result_buf.s_name, result_buf.s_proto,
ntohs(result_buf.s_port));
for (p = result_buf.s_aliases; *p != NULL; p++)
printf("%s ", *p);
printf("\n");
exit(EXIT_SUCCESS);
}
getservent(3), services(5)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
GNU 2010-09-10 GETSERVENT_R(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface