'\" t .\" Copyright 2008, Linux Foundation, written by Michael Kerrisk .\" .\" .\" SPDX-License-Identifier: Linux-man-pages-copyleft .\" .TH getservent_r 3 2023-03-30 "Linux man-pages 6.04" .SH NAME getservent_r, getservbyname_r, getservbyport_r \- get service entry (reentrant) .SH LIBRARY Standard C library .RI ( libc ", " \-lc ) .SH SYNOPSIS .nf .B #include .PP .BI "int getservent_r(struct servent *restrict " result_buf , .BI " char " buf "[restrict ." buflen "], size_t " buflen , .BI " struct servent **restrict " result ); .BI "int getservbyname_r(const char *restrict " name , .BI " const char *restrict " proto , .BI " struct servent *restrict " result_buf , .BI " char " buf "[restrict ." buflen "], size_t " buflen , .BI " struct servent **restrict " result ); .BI "int getservbyport_r(int " port , .BI " const char *restrict " proto , .BI " struct servent *restrict " result_buf , .BI " char " buf "[restrict ." buflen "], size_t " buflen , .BI " struct servent **restrict " result ); .PP .fi .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .PP .BR getservent_r (), .BR getservbyname_r (), .BR getservbyport_r (): .nf Since glibc 2.19: _DEFAULT_SOURCE glibc 2.19 and earlier: _BSD_SOURCE || _SVID_SOURCE .fi .SH DESCRIPTION The .BR getservent_r (), .BR getservbyname_r (), and .BR getservbyport_r () functions are the reentrant equivalents of, respectively, .BR getservent (3), .BR getservbyname (3), and .BR getservbyport (3). They differ in the way that the .I servent structure is returned, and in the function calling signature and return value. This manual page describes just the differences from the nonreentrant functions. .PP Instead of returning a pointer to a statically allocated .I servent structure as the function result, these functions copy the structure into the location pointed to by .IR result_buf . .PP The .I buf array is used to store the string fields pointed to by the returned .I servent structure. (The nonreentrant functions allocate these strings in static storage.) The size of this array is specified in .IR buflen . If .I buf is too small, the call fails with the error .BR ERANGE , and the caller must try again with a larger buffer. (A buffer of length 1024 bytes should be sufficient for most applications.) .\" I can find no information on the required/recommended buffer size; .\" the nonreentrant functions use a 1024 byte buffer -- mtk. .PP If the function call successfully obtains a service record, then .I *result is set pointing to .IR result_buf ; otherwise, .I *result is set to NULL. .SH RETURN VALUE On success, these functions return 0. On error, they return one of the positive error numbers listed in errors. .PP On error, record not found .RB ( getservbyname_r (), .BR getservbyport_r ()), or end of input .RB ( getservent_r ()) .I result is set to NULL. .SH ERRORS .TP .B ENOENT .RB ( getservent_r ()) No more records in database. .TP .B ERANGE .I buf is too small. Try again with a larger buffer (and increased .IR buflen ). .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .ad l .nh .TS allbox; lbx lb lb l l l. Interface Attribute Value T{ .BR getservent_r (), .BR getservbyname_r (), .BR getservbyport_r () T} Thread safety MT-Safe locale .TE .hy .ad .sp 1 .SH VERSIONS Functions with similar names exist on some other systems, though typically with different calling signatures. .SH STANDARDS GNU. .SH EXAMPLES The program below uses .BR 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 .IR buflen ; if .BR getservbyport_r () fails with the error .BR ERANGE , the program retries with larger buffer sizes. The following shell session shows a couple of sample runs: .PP .in +4n .EX .RB "$" " ./a.out 7 tcp 1" ERANGE! Retrying with larger buffer getservbyport_r() returned: 0 (success) (buflen=87) s_name=echo; s_proto=tcp; s_port=7; aliases= .RB "$" " ./a.out 77777 tcp" getservbyport_r() returned: 0 (success) (buflen=1024) Call failed/record not found .EE .in .SS Program source \& .\" SRC BEGIN (getservent_r.c) .EX #define _GNU_SOURCE #include #include #include #include #include #include #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; if (argc < 3) { printf("Usage: %s port\-num proto\-name [buflen]\en", 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)\en", 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\en"); 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)\en", MAX_BUF); exit(EXIT_FAILURE); } } } while (s == ERANGE); printf("getservbyport_r() returned: %s (buflen=%d)\en", (s == 0) ? "0 (success)" : (s == ENOENT) ? "ENOENT" : strerror(s), buflen); if (s != 0 || result == NULL) { printf("Call failed/record not found\en"); 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 (char **p = result_buf.s_aliases; *p != NULL; p++) printf("%s ", *p); printf("\en"); exit(EXIT_SUCCESS); } .EE .\" SRC END .SH SEE ALSO .BR getservent (3), .BR services (5)