1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * circular buffer syslog implementation for busybox
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4 | *
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5 | * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
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6 | *
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7 | * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
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8 | *
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9 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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10 | */
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11 | //config:config LOGREAD
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12 | //config: bool "logread"
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13 | //config: default y
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14 | //config: depends on FEATURE_IPC_SYSLOG
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15 | //config: help
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16 | //config: If you enabled Circular Buffer support, you almost
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17 | //config: certainly want to enable this feature as well. This
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18 | //config: utility will allow you to read the messages that are
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19 | //config: stored in the syslogd circular buffer.
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20 | //config:
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21 | //config:config FEATURE_LOGREAD_REDUCED_LOCKING
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22 | //config: bool "Double buffering"
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23 | //config: default y
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24 | //config: depends on LOGREAD
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25 | //config: help
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26 | //config: 'logread' ouput to slow serial terminals can have
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27 | //config: side effects on syslog because of the semaphore.
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28 | //config: This option make logread to double buffer copy
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29 | //config: from circular buffer, minimizing semaphore
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30 | //config: contention at some minor memory expense.
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31 | //config:
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32 |
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33 | //applet:IF_LOGREAD(APPLET(logread, BB_DIR_SBIN, BB_SUID_DROP))
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34 |
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35 | //kbuild:lib-$(CONFIG_LOGREAD) += logread.o
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36 |
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37 | //usage:#define logread_trivial_usage
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38 | //usage: "[-fF]"
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39 | //usage:#define logread_full_usage "\n\n"
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40 | //usage: "Show messages in syslogd's circular buffer\n"
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41 | //usage: "\n -f Output data as log grows"
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42 | //usage: "\n -F Same as -f, but dump buffer first"
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43 |
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44 | #include "libbb.h"
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45 | #include "common_bufsiz.h"
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46 | #include <sys/ipc.h>
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47 | #include <sys/sem.h>
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48 | #include <sys/shm.h>
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49 |
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50 | #define DEBUG 0
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51 |
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52 | /* our shared key (syslogd.c and logread.c must be in sync) */
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53 | enum { KEY_ID = 0x414e4547 }; /* "GENA" */
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54 |
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55 | struct shbuf_ds {
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56 | int32_t size; // size of data - 1
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57 | int32_t tail; // end of message list
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58 | char data[1]; // messages
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59 | };
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60 |
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61 | static const struct sembuf init_sem[3] = {
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62 | {0, -1, IPC_NOWAIT | SEM_UNDO},
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63 | {1, 0}, {0, +1, SEM_UNDO}
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64 | };
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65 |
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66 | struct globals {
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67 | struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
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68 | struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
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69 | struct shbuf_ds *shbuf;
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70 | } FIX_ALIASING;
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71 | #define G (*(struct globals*)bb_common_bufsiz1)
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72 | #define SMrup (G.SMrup)
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73 | #define SMrdn (G.SMrdn)
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74 | #define shbuf (G.shbuf)
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75 | #define INIT_G() do { \
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76 | setup_common_bufsiz(); \
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77 | memcpy(SMrup, init_sem, sizeof(init_sem)); \
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78 | } while (0)
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79 |
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80 | #if 0
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81 | static void error_exit(const char *str) NORETURN;
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82 | static void error_exit(const char *str)
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83 | {
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84 | /* Release all acquired resources */
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85 | shmdt(shbuf);
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86 | bb_perror_msg_and_die(str);
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87 | }
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88 | #else
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89 | /* On Linux, shmdt is not mandatory on exit */
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90 | # define error_exit(str) bb_perror_msg_and_die(str)
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91 | #endif
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92 |
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93 | /*
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94 | * sem_up - up()'s a semaphore.
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95 | */
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96 | static void sem_up(int semid)
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97 | {
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98 | if (semop(semid, SMrup, 1) == -1)
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99 | error_exit("semop[SMrup]");
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100 | }
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101 |
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102 | static void interrupted(int sig)
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103 | {
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104 | /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */
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105 | kill_myself_with_sig(sig);
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106 | }
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107 |
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108 | int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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109 | int logread_main(int argc UNUSED_PARAM, char **argv)
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110 | {
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111 | unsigned cur;
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112 | int log_semid; /* ipc semaphore id */
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113 | int log_shmid; /* ipc shared memory id */
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114 | int follow = getopt32(argv, "fF");
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115 |
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116 | INIT_G();
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117 |
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118 | log_shmid = shmget(KEY_ID, 0, 0);
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119 | if (log_shmid == -1)
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120 | bb_perror_msg_and_die("can't %s syslogd buffer", "find");
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121 |
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122 | /* Attach shared memory to our char* */
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123 | shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
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124 | if (shbuf == NULL)
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125 | bb_perror_msg_and_die("can't %s syslogd buffer", "access");
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126 |
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127 | log_semid = semget(KEY_ID, 0, 0);
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128 | if (log_semid == -1)
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129 | error_exit("can't get access to semaphores for syslogd buffer");
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130 |
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131 | bb_signals(BB_FATAL_SIGS, interrupted);
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132 |
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133 | /* Suppose atomic memory read */
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134 | /* Max possible value for tail is shbuf->size - 1 */
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135 | cur = shbuf->tail;
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136 |
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137 | /* Loop for -f or -F, one pass otherwise */
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138 | do {
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139 | unsigned shbuf_size;
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140 | unsigned shbuf_tail;
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141 | const char *shbuf_data;
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142 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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143 | int i;
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144 | int len_first_part;
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145 | int len_total = len_total; /* for gcc */
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146 | char *copy = copy; /* for gcc */
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147 | #endif
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148 | if (semop(log_semid, SMrdn, 2) == -1)
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149 | error_exit("semop[SMrdn]");
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150 |
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151 | /* Copy the info, helps gcc to realize that it doesn't change */
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152 | shbuf_size = shbuf->size;
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153 | shbuf_tail = shbuf->tail;
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154 | shbuf_data = shbuf->data; /* pointer! */
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155 |
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156 | if (DEBUG)
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157 | printf("cur:%u tail:%u size:%u\n",
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158 | cur, shbuf_tail, shbuf_size);
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159 |
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160 | if (!(follow & 1)) { /* not -f */
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161 | /* if -F, "convert" it to -f, so that we dont
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162 | * dump the entire buffer on each iteration
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163 | */
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164 | follow >>= 1;
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165 |
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166 | /* advance to oldest complete message */
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167 | /* find NUL */
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168 | cur += strlen(shbuf_data + cur);
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169 | if (cur >= shbuf_size) { /* last byte in buffer? */
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170 | cur = strnlen(shbuf_data, shbuf_tail);
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171 | if (cur == shbuf_tail)
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172 | goto unlock; /* no complete messages */
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173 | }
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174 | /* advance to first byte of the message */
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175 | cur++;
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176 | if (cur >= shbuf_size) /* last byte in buffer? */
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177 | cur = 0;
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178 | } else { /* -f */
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179 | if (cur == shbuf_tail) {
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180 | sem_up(log_semid);
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181 | fflush_all();
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182 | sleep(1); /* TODO: replace me with a sleep_on */
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183 | continue;
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184 | }
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185 | }
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186 |
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187 | /* Read from cur to tail */
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188 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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189 | len_first_part = len_total = shbuf_tail - cur;
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190 | if (len_total < 0) {
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191 | /* message wraps: */
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192 | /* [SECOND PART.........FIRST PART] */
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193 | /* ^data ^tail ^cur ^size */
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194 | len_total += shbuf_size;
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195 | }
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196 | copy = xmalloc(len_total + 1);
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197 | if (len_first_part < 0) {
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198 | /* message wraps (see above) */
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199 | len_first_part = shbuf_size - cur;
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200 | memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
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201 | }
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202 | memcpy(copy, shbuf_data + cur, len_first_part);
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203 | copy[len_total] = '\0';
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204 | cur = shbuf_tail;
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205 | #else
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206 | while (cur != shbuf_tail) {
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207 | fputs(shbuf_data + cur, stdout);
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208 | cur += strlen(shbuf_data + cur) + 1;
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209 | if (cur >= shbuf_size)
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210 | cur = 0;
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211 | }
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212 | #endif
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213 | unlock:
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214 | /* release the lock on the log chain */
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215 | sem_up(log_semid);
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216 |
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217 | #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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218 | for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
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219 | fputs(copy + i, stdout);
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220 | }
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221 | free(copy);
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222 | #endif
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223 | fflush_all();
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224 | } while (follow);
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225 |
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226 | /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */
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227 |
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228 | fflush_stdout_and_exit(EXIT_SUCCESS);
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229 | }
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