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 tarball for details.
  10  */
  11
  12 #include "busybox.h"
  13 #include <sys/ipc.h>
  14 #include <sys/sem.h>
  15 #include <sys/shm.h>
  16
  17 #define DEBUG 0
  18
  19 enum { KEY_ID = 0x414e4547 }; /* "GENA" */
  20
  21 static struct shbuf_ds {
  22         int32_t size;           // size of data written
  23         int32_t head;           // start of message list
  24         int32_t tail;           // end of message list
  25         char data[1];           // data/messages
  26 } *buf;                         // shared memory pointer
  27
  28 // Semaphore operation structures
  29 static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
  30 static struct sembuf SMrdn[2] = {{1, 0}, {0, +1, SEM_UNDO}}; // set SMrdn
  31
  32
  33 static void error_exit(const char *str) ATTRIBUTE_NORETURN;
  34 static void error_exit(const char *str)
  35 {
  36         //release all acquired resources
  37         shmdt(buf);
  38         bb_perror_msg_and_die(str);
  39 }
  40
  41 /*
  42  * sem_up - up()'s a semaphore.
  43  */
  44 static void sem_up(int semid)
  45 {
  46         if (semop(semid, SMrup, 1) == -1)
  47                 error_exit("semop[SMrup]");
  48 }
  49
  50 static void interrupted(int sig ATTRIBUTE_UNUSED)
  51 {
  52         signal(SIGINT, SIG_IGN);
  53         shmdt(buf);
  54         exit(0);
  55 }
  56
  57 int logread_main(int argc, char **argv);
  58 int logread_main(int argc, char **argv)
  59 {
  60         int cur;
  61         int log_semid; /* ipc semaphore id */
  62         int log_shmid; /* ipc shared memory id */
  63         smallint follow = getopt32(argc, argv, "f");
  64
  65         log_shmid = shmget(KEY_ID, 0, 0);
  66         if (log_shmid == -1)
  67                 bb_perror_msg_and_die("can't find syslogd buffer");
  68
  69         // Attach shared memory to our char*
  70         buf = shmat(log_shmid, NULL, SHM_RDONLY);
  71         if (buf == NULL)
  72                 bb_perror_msg_and_die("can't access syslogd buffer");
  73
  74         log_semid = semget(KEY_ID, 0, 0);
  75         if (log_semid == -1)
  76                 error_exit("can't get access to semaphores for syslogd buffer");
  77
  78         // attempt to redefine ^C signal
  79         signal(SIGINT, interrupted);
  80
  81         // Suppose atomic memory move
  82         cur = follow ? buf->tail : buf->head;
  83
  84         do {
  85 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
  86                 char *buf_data;
  87                 int log_len, j;
  88 #endif
  89                 if (semop(log_semid, SMrdn, 2) == -1)
  90                         error_exit("semop[SMrdn]");
  91
  92                 if (DEBUG)
  93                         printf("head:%i cur:%d tail:%i size:%i\n",
  94                                         buf->head, cur, buf->tail, buf->size);
  95
  96                 if (buf->head == buf->tail || cur == buf->tail) {
  97                         if (follow) {
  98                                 sem_up(log_semid);
  99                                 fflush(stdout);
 100                                 sleep(1); /* TODO: replace me with a sleep_on */
 101                                 continue;
 102                         }
 103                         puts("<empty syslog>");
 104                 }
 105
 106                 // Read Memory
 107 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 108                 log_len = buf->tail - cur;
 109                 if (log_len < 0)
 110                         log_len += buf->size;
 111                 buf_data = xmalloc(log_len);
 112
 113                 if (buf->tail >= cur)
 114                         j = log_len;
 115                 else
 116                         j = buf->size - cur;
 117                 memcpy(buf_data, buf->data + cur, j);
 118
 119                 if (buf->tail < cur)
 120                         memcpy(buf_data + buf->size - cur, buf->data, buf->tail);
 121                 cur = buf->tail;
 122 #else
 123                 while (cur != buf->tail) {
 124                         fputs(buf->data + cur, stdout);
 125                         cur += strlen(buf->data + cur) + 1;
 126                         if (cur >= buf->size)
 127                                 cur = 0;
 128                 }
 129 #endif
 130                 // release the lock on the log chain
 131                 sem_up(log_semid);
 132
 133 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 134                 for (j = 0; j < log_len; j += strlen(buf_data+j) + 1) {
 135                         fputs(buf_data + j, stdout);
 136                 }
 137                 free(buf_data);
 138 #endif
 139         } while (follow);
 140
 141         shmdt(buf);
 142
 143         fflush_stdout_and_exit(EXIT_SUCCESS);
 144 }