[821] | 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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[2725] | 9 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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[821] | 10 | */
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[3621] | 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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[821] | 32 |
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[3621] | 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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[3232] | 37 | //usage:#define logread_trivial_usage
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[3621] | 38 | //usage: "[-fF]"
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[3232] | 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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[3621] | 42 | //usage: "\n -F Same as -f, but dump buffer first"
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[3232] | 43 |
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[1765] | 44 | #include "libbb.h"
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[3621] | 45 | #include "common_bufsiz.h"
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[821] | 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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[1765] | 50 | #define DEBUG 0
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[821] | 51 |
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[2725] | 52 | /* our shared key (syslogd.c and logread.c must be in sync) */
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[1765] | 53 | enum { KEY_ID = 0x414e4547 }; /* "GENA" */
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| 54 |
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[2725] | 55 | struct shbuf_ds {
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[1765] | 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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[2725] | 59 | };
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[821] | 60 |
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[2725] | 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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[821] | 65 |
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[2725] | 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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[3621] | 71 | #define G (*(struct globals*)bb_common_bufsiz1)
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[2725] | 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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[3621] | 76 | setup_common_bufsiz(); \
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[2725] | 77 | memcpy(SMrup, init_sem, sizeof(init_sem)); \
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| 78 | } while (0)
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[821] | 79 |
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[3621] | 80 | #if 0
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[2725] | 81 | static void error_exit(const char *str) NORETURN;
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[1765] | 82 | static void error_exit(const char *str)
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| 83 | {
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[3621] | 84 | /* Release all acquired resources */
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[1765] | 85 | shmdt(shbuf);
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| 86 | bb_perror_msg_and_die(str);
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| 87 | }
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[3621] | 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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[821] | 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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[1765] | 96 | static void sem_up(int semid)
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[821] | 97 | {
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[1765] | 98 | if (semop(semid, SMrup, 1) == -1)
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[821] | 99 | error_exit("semop[SMrup]");
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| 100 | }
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| 101 |
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[3621] | 102 | static void interrupted(int sig)
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[821] | 103 | {
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[3621] | 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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[821] | 106 | }
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| 107 |
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[2725] | 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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[821] | 110 | {
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[2725] | 111 | unsigned cur;
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[1765] | 112 | int log_semid; /* ipc semaphore id */
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| 113 | int log_shmid; /* ipc shared memory id */
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[3621] | 114 | int follow = getopt32(argv, "fF");
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[821] | 115 |
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[2725] | 116 | INIT_G();
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| 117 |
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[1765] | 118 | log_shmid = shmget(KEY_ID, 0, 0);
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| 119 | if (log_shmid == -1)
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[3621] | 120 | bb_perror_msg_and_die("can't %s syslogd buffer", "find");
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[821] | 121 |
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[1765] | 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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[3621] | 125 | bb_perror_msg_and_die("can't %s syslogd buffer", "access");
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[821] | 126 |
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[1765] | 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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[3621] | 131 | bb_signals(BB_FATAL_SIGS, interrupted);
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[821] | 132 |
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[1765] | 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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[821] | 136 |
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[3621] | 137 | /* Loop for -f or -F, one pass otherwise */
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[821] | 138 | do {
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[1765] | 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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[821] | 147 | #endif
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[1765] | 148 | if (semop(log_semid, SMrdn, 2) == -1)
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| 149 | error_exit("semop[SMrdn]");
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[821] | 150 |
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[1765] | 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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[821] | 155 |
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[1765] | 156 | if (DEBUG)
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[3621] | 157 | printf("cur:%u tail:%u size:%u\n",
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[1765] | 158 | cur, shbuf_tail, shbuf_size);
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| 159 |
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[3621] | 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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[1765] | 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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[3621] | 178 | } else { /* -f */
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[1765] | 179 | if (cur == shbuf_tail) {
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[821] | 180 | sem_up(log_semid);
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[2725] | 181 | fflush_all();
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[1765] | 182 | sleep(1); /* TODO: replace me with a sleep_on */
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[821] | 183 | continue;
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| 184 | }
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| 185 | }
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| 186 |
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[1765] | 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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[821] | 195 | }
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[1765] | 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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[821] | 205 | #else
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[1765] | 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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[821] | 211 | }
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| 212 | #endif
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[1765] | 213 | unlock:
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| 214 | /* release the lock on the log chain */
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[821] | 215 | sem_up(log_semid);
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| 216 |
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[1765] | 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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[821] | 220 | }
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[1765] | 221 | free(copy);
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[821] | 222 | #endif
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[3621] | 223 | fflush_all();
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[821] | 224 | } while (follow);
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| 225 |
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[3621] | 226 | /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */
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[821] | 227 |
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[1765] | 228 | fflush_stdout_and_exit(EXIT_SUCCESS);
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[821] | 229 | }
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