sysklogd/logread.c

   1 /* vi: set sw=4 ts=4: */
   2 /*
   3  * circular buffer syslog implementation for busybox
   4  *
   5  * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
   6  *
   7  * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
   8  *
   9  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  10  */
  11
  12 //usage:#define logread_trivial_usage
  13 //usage:       "[-f]"
  14 //usage:#define logread_full_usage "\n\n"
  15 //usage:       "Show messages in syslogd's circular buffer\n"
  16 //usage:     "\nOptions:"
  17 //usage:     "\n        -f      Output data as log grows"
  18
  19 #include "libbb.h"
  20 #include <sys/ipc.h>
  21 #include <sys/sem.h>
  22 #include <sys/shm.h>
  23
  24 #define DEBUG 0
  25
  26 /* our shared key (syslogd.c and logread.c must be in sync) */
  27 enum { KEY_ID = 0x414e4547 }; /* "GENA" */
  28
  29 struct shbuf_ds {
  30         int32_t size;           // size of data - 1
  31         int32_t tail;           // end of message list
  32         char data[1];           // messages
  33 };
  34
  35 static const struct sembuf init_sem[3] = {
  36         {0, -1, IPC_NOWAIT | SEM_UNDO},
  37         {1, 0}, {0, +1, SEM_UNDO}
  38 };
  39
  40 struct globals {
  41         struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
  42         struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
  43         struct shbuf_ds *shbuf;
  44 } FIX_ALIASING;
  45 #define G (*(struct globals*)&bb_common_bufsiz1)
  46 #define SMrup (G.SMrup)
  47 #define SMrdn (G.SMrdn)
  48 #define shbuf (G.shbuf)
  49 #define INIT_G() do { \
  50         memcpy(SMrup, init_sem, sizeof(init_sem)); \
  51 } while (0)
  52
  53 static void error_exit(const char *str) NORETURN;
  54 static void error_exit(const char *str)
  55 {
  56         //release all acquired resources
  57         shmdt(shbuf);
  58         bb_perror_msg_and_die(str);
  59 }
  60
  61 /*
  62  * sem_up - up()'s a semaphore.
  63  */
  64 static void sem_up(int semid)
  65 {
  66         if (semop(semid, SMrup, 1) == -1)
  67                 error_exit("semop[SMrup]");
  68 }
  69
  70 static void interrupted(int sig UNUSED_PARAM)
  71 {
  72         signal(SIGINT, SIG_IGN);
  73         shmdt(shbuf);
  74         exit(EXIT_SUCCESS);
  75 }
  76
  77 int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  78 int logread_main(int argc UNUSED_PARAM, char **argv)
  79 {
  80         unsigned cur;
  81         int log_semid; /* ipc semaphore id */
  82         int log_shmid; /* ipc shared memory id */
  83         smallint follow = getopt32(argv, "f");
  84
  85         INIT_G();
  86
  87         log_shmid = shmget(KEY_ID, 0, 0);
  88         if (log_shmid == -1)
  89                 bb_perror_msg_and_die("can't find syslogd buffer");
  90
  91         /* Attach shared memory to our char* */
  92         shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
  93         if (shbuf == NULL)
  94                 bb_perror_msg_and_die("can't access syslogd buffer");
  95
  96         log_semid = semget(KEY_ID, 0, 0);
  97         if (log_semid == -1)
  98                 error_exit("can't get access to semaphores for syslogd buffer");
  99
 100         signal(SIGINT, interrupted);
 101
 102         /* Suppose atomic memory read */
 103         /* Max possible value for tail is shbuf->size - 1 */
 104         cur = shbuf->tail;
 105
 106         /* Loop for logread -f, one pass if there was no -f */
 107         do {
 108                 unsigned shbuf_size;
 109                 unsigned shbuf_tail;
 110                 const char *shbuf_data;
 111 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 112                 int i;
 113                 int len_first_part;
 114                 int len_total = len_total; /* for gcc */
 115                 char *copy = copy; /* for gcc */
 116 #endif
 117                 if (semop(log_semid, SMrdn, 2) == -1)
 118                         error_exit("semop[SMrdn]");
 119
 120                 /* Copy the info, helps gcc to realize that it doesn't change */
 121                 shbuf_size = shbuf->size;
 122                 shbuf_tail = shbuf->tail;
 123                 shbuf_data = shbuf->data; /* pointer! */
 124
 125                 if (DEBUG)
 126                         printf("cur:%d tail:%i size:%i\n",
 127                                         cur, shbuf_tail, shbuf_size);
 128
 129                 if (!follow) {
 130                         /* advance to oldest complete message */
 131                         /* find NUL */
 132                         cur += strlen(shbuf_data + cur);
 133                         if (cur >= shbuf_size) { /* last byte in buffer? */
 134                                 cur = strnlen(shbuf_data, shbuf_tail);
 135                                 if (cur == shbuf_tail)
 136                                         goto unlock; /* no complete messages */
 137                         }
 138                         /* advance to first byte of the message */
 139                         cur++;
 140                         if (cur >= shbuf_size) /* last byte in buffer? */
 141                                 cur = 0;
 142                 } else { /* logread -f */
 143                         if (cur == shbuf_tail) {
 144                                 sem_up(log_semid);
 145                                 fflush_all();
 146                                 sleep(1); /* TODO: replace me with a sleep_on */
 147                                 continue;
 148                         }
 149                 }
 150
 151                 /* Read from cur to tail */
 152 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 153                 len_first_part = len_total = shbuf_tail - cur;
 154                 if (len_total < 0) {
 155                         /* message wraps: */
 156                         /* [SECOND PART.........FIRST PART] */
 157                         /*  ^data      ^tail    ^cur      ^size */
 158                         len_total += shbuf_size;
 159                 }
 160                 copy = xmalloc(len_total + 1);
 161                 if (len_first_part < 0) {
 162                         /* message wraps (see above) */
 163                         len_first_part = shbuf_size - cur;
 164                         memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
 165                 }
 166                 memcpy(copy, shbuf_data + cur, len_first_part);
 167                 copy[len_total] = '\0';
 168                 cur = shbuf_tail;
 169 #else
 170                 while (cur != shbuf_tail) {
 171                         fputs(shbuf_data + cur, stdout);
 172                         cur += strlen(shbuf_data + cur) + 1;
 173                         if (cur >= shbuf_size)
 174                                 cur = 0;
 175                 }
 176 #endif
 177  unlock:
 178                 /* release the lock on the log chain */
 179                 sem_up(log_semid);
 180
 181 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 182                 for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
 183                         fputs(copy + i, stdout);
 184                 }
 185                 free(copy);
 186 #endif
 187         } while (follow);
 188
 189         shmdt(shbuf);
 190
 191         fflush_stdout_and_exit(EXIT_SUCCESS);
 192 }