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