| | 1 | /* -*-c-*- |
| | 2 | * |
| | 3 | * $Id: lock.c,v 1.6 2004/04/08 01:36:13 mdw Exp $ |
| | 4 | * |
| | 5 | * Simplified POSIX locking interface |
| | 6 | * |
| | 7 | * (c) 1997 Straylight/Edgeware |
| | 8 | */ |
| | 9 | |
| | 10 | /*----- Licensing notice --------------------------------------------------* |
| | 11 | * |
| | 12 | * This file is part of the mLib utilities library. |
| | 13 | * |
| | 14 | * mLib is free software; you can redistribute it and/or modify |
| | 15 | * it under the terms of the GNU Library General Public License as |
| | 16 | * published by the Free Software Foundation; either version 2 of the |
| | 17 | * License, or (at your option) any later version. |
| | 18 | * |
| | 19 | * mLib is distributed in the hope that it will be useful, |
| | 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| | 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| | 22 | * GNU Library General Public License for more details. |
| | 23 | * |
| | 24 | * You should have received a copy of the GNU Library General Public |
| | 25 | * License along with mLib; if not, write to the Free |
| | 26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| | 27 | * MA 02111-1307, USA. |
| | 28 | */ |
| | 29 | |
| | 30 | /*----- Header files ------------------------------------------------------*/ |
| | 31 | |
| | 32 | #include <errno.h> |
| | 33 | #include <setjmp.h> |
| | 34 | #include <signal.h> |
| | 35 | #include <stdio.h> |
| | 36 | #include <stdlib.h> |
| | 37 | #include <string.h> |
| | 38 | #include <time.h> |
| | 39 | |
| | 40 | #include <sys/types.h> |
| | 41 | #include <unistd.h> |
| | 42 | #include <fcntl.h> |
| | 43 | |
| | 44 | #include "lock.h" |
| | 45 | |
| | 46 | /*----- Tunable constants -------------------------------------------------*/ |
| | 47 | |
| | 48 | #define LOCK_TIMEOUT 10 /* Maximum time in seconds to wait */ |
| | 49 | |
| | 50 | /*----- Static variables --------------------------------------------------*/ |
| | 51 | |
| | 52 | static jmp_buf jmp; /* Jump here to interrup @fcntl@ */ |
| | 53 | |
| | 54 | /*----- Main code ---------------------------------------------------------*/ |
| | 55 | |
| | 56 | /* --- @sigalrm@ --- * |
| | 57 | * |
| | 58 | * Arguments: @int sig@ = signal number |
| | 59 | * |
| | 60 | * Returns: --- |
| | 61 | * |
| | 62 | * Use: Makes sure that a @SIGALRM@ signal interrupts system calls. |
| | 63 | */ |
| | 64 | |
| | 65 | static void sigalrm(int sig) { longjmp(jmp, 1); } |
| | 66 | |
| | 67 | /* --- @lock_file@ --- * |
| | 68 | * |
| | 69 | * Arguments: @int fd@ = file descriptor to lock |
| | 70 | * @unsigned how@ = type of lock required |
| | 71 | * |
| | 72 | * Returns: 0 if OK, -1 if it failed. |
| | 73 | * |
| | 74 | * Use: Acquires a lock on the given file. The value @how@ |
| | 75 | * specifies the type of lock to acquire: @LOCK_EXCL@ gets |
| | 76 | * an exclusive (write) lock; @LOCK_NONEXCL@ gets a non- |
| | 77 | * exclusive (read) lock and @LOCK_UNLOCK@ releases any locks. |
| | 78 | * Acquiring a lock gets timed out after a while with an |
| | 79 | * error. |
| | 80 | */ |
| | 81 | |
| | 82 | int lock_file(int fd, unsigned how) |
| | 83 | { |
| | 84 | struct flock fk; |
| | 85 | struct sigaction sa, osa; |
| | 86 | sigset_t ss, oss; |
| | 87 | int e; |
| | 88 | int al, d, left; |
| | 89 | |
| | 90 | /* --- Fill in the easy bits --- */ |
| | 91 | |
| | 92 | fk.l_whence = SEEK_SET; |
| | 93 | fk.l_start = 0; |
| | 94 | fk.l_len = 0; |
| | 95 | |
| | 96 | /* --- Unlocking is really easy --- */ |
| | 97 | |
| | 98 | if (how == LOCK_UNLOCK) { |
| | 99 | fk.l_type = F_UNLCK; |
| | 100 | return (fcntl(fd, F_SETLK, &fk)); |
| | 101 | } |
| | 102 | |
| | 103 | /* --- Decide how to do the locking --- */ |
| | 104 | |
| | 105 | if (how == LOCK_EXCL) |
| | 106 | fk.l_type = F_WRLCK; |
| | 107 | else if (how == LOCK_NONEXCL) |
| | 108 | fk.l_type = F_RDLCK; |
| | 109 | else { |
| | 110 | errno = EINVAL; |
| | 111 | return (-1); |
| | 112 | } |
| | 113 | |
| | 114 | /* --- Block @SIGALRM@ for a while --- * |
| | 115 | * |
| | 116 | * I don't want stray alarms going off while I'm busy here. |
| | 117 | */ |
| | 118 | |
| | 119 | sigemptyset(&ss); |
| | 120 | sigaddset(&ss, SIGALRM); |
| | 121 | if (sigprocmask(SIG_BLOCK, &ss, &oss)) |
| | 122 | return (-1); |
| | 123 | |
| | 124 | /* --- Set up the signal handler --- */ |
| | 125 | |
| | 126 | sa.sa_handler = sigalrm; |
| | 127 | sa.sa_flags = 0; |
| | 128 | #ifdef SA_INTERRUPT |
| | 129 | sa.sa_flags |= SA_INTERRUPT; |
| | 130 | #endif |
| | 131 | sigemptyset(&sa.sa_mask); |
| | 132 | if (sigaction(SIGALRM, &sa, &osa)) |
| | 133 | return (-1); |
| | 134 | |
| | 135 | /* --- Set up the alarm, remembering when it's meant to go off --- */ |
| | 136 | |
| | 137 | al = alarm(0); |
| | 138 | if (al && al < LOCK_TIMEOUT) |
| | 139 | d = al; |
| | 140 | else |
| | 141 | d = LOCK_TIMEOUT; |
| | 142 | alarm(d); |
| | 143 | |
| | 144 | /* --- Set up the return context for the signal handler --- */ |
| | 145 | |
| | 146 | if (setjmp(jmp)) { |
| | 147 | sigprocmask(SIG_SETMASK, &oss, 0); |
| | 148 | errno = EINTR; |
| | 149 | e = -1; |
| | 150 | goto done; |
| | 151 | } |
| | 152 | |
| | 153 | /* --- Unblock the signal and we're ready --- */ |
| | 154 | |
| | 155 | if (sigprocmask(SIG_SETMASK, &oss, 0)) { |
| | 156 | alarm(al); |
| | 157 | e = -1; |
| | 158 | goto done; |
| | 159 | } |
| | 160 | |
| | 161 | /* --- Do it --- */ |
| | 162 | |
| | 163 | e = fcntl(fd, F_SETLKW, &fk); |
| | 164 | |
| | 165 | /* --- Tidy up the mess I left --- */ |
| | 166 | |
| | 167 | left = alarm(0); |
| | 168 | if (al) |
| | 169 | alarm(al - d + left); |
| | 170 | done: |
| | 171 | sigaction(SIGALRM, &osa, 0); |
| | 172 | return (e); |
| | 173 | } |
| | 174 | |
| | 175 | /*----- That's all, fokls -------------------------------------------------*/ |
~mdw / mLib / blame_incremental