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 "libbb.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 - 1
  23         int32_t tail;           // end of message list
  24         char data[1];           // messages
  25 } *shbuf;
  26
  27 // Semaphore operation structures
  28 static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
  29 static struct sembuf SMrdn[2] = {{1, 0}, {0, +1, SEM_UNDO}}; // set SMrdn
  30
  31
  32 static void error_exit(const char *str) ATTRIBUTE_NORETURN;
  33 static void error_exit(const char *str)
  34 {
  35         //release all acquired resources
  36         shmdt(shbuf);
  37         bb_perror_msg_and_die(str);
  38 }
  39
  40 /*
  41  * sem_up - up()'s a semaphore.
  42  */
  43 static void sem_up(int semid)
  44 {
  45         if (semop(semid, SMrup, 1) == -1)
  46                 error_exit("semop[SMrup]");
  47 }
  48
  49 static void interrupted(int sig ATTRIBUTE_UNUSED)
  50 {
  51         signal(SIGINT, SIG_IGN);
  52         shmdt(shbuf);
  53         exit(0);
  54 }
  55
  56 int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  57 int logread_main(int argc, char **argv)
  58 {
  59         int cur;
  60         int log_semid; /* ipc semaphore id */
  61         int log_shmid; /* ipc shared memory id */
  62         smallint follow = getopt32(argv, "f");
  63
  64         log_shmid = shmget(KEY_ID, 0, 0);
  65         if (log_shmid == -1)
  66                 bb_perror_msg_and_die("can't find syslogd buffer");
  67
  68         /* Attach shared memory to our char* */
  69         shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
  70         if (shbuf == NULL)
  71                 bb_perror_msg_and_die("can't access syslogd buffer");
  72
  73         log_semid = semget(KEY_ID, 0, 0);
  74         if (log_semid == -1)
  75                 error_exit("can't get access to semaphores for syslogd buffer");
  76
  77         signal(SIGINT, interrupted);
  78
  79         /* Suppose atomic memory read */
  80         /* Max possible value for tail is shbuf->size - 1 */
  81         cur = shbuf->tail;
  82
  83         /* Loop for logread -f, one pass if there was no -f */
  84         do {
  85                 unsigned shbuf_size;
  86                 unsigned shbuf_tail;
  87                 const char *shbuf_data;
  88 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
  89                 int i;
  90                 int len_first_part;
  91                 int len_total = len_total; /* for gcc */
  92                 char *copy = copy; /* for gcc */
  93 #endif
  94                 if (semop(log_semid, SMrdn, 2) == -1)
  95                         error_exit("semop[SMrdn]");
  96
  97                 /* Copy the info, helps gcc to realize that it doesn't change */
  98                 shbuf_size = shbuf->size;
  99                 shbuf_tail = shbuf->tail;
 100                 shbuf_data = shbuf->data; /* pointer! */
 101
 102                 if (DEBUG)
 103                         printf("cur:%d tail:%i size:%i\n",
 104                                         cur, shbuf_tail, shbuf_size);
 105
 106                 if (!follow) {
 107                         /* advance to oldest complete message */
 108                         /* find NUL */
 109                         cur += strlen(shbuf_data + cur);
 110                         if (cur >= shbuf_size) { /* last byte in buffer? */
 111                                 cur = strnlen(shbuf_data, shbuf_tail);
 112                                 if (cur == shbuf_tail)
 113                                         goto unlock; /* no complete messages */
 114                         }
 115                         /* advance to first byte of the message */
 116                         cur++;
 117                         if (cur >= shbuf_size) /* last byte in buffer? */
 118                                 cur = 0;
 119                 } else { /* logread -f */
 120                         if (cur == shbuf_tail) {
 121                                 sem_up(log_semid);
 122                                 fflush(stdout);
 123                                 sleep(1); /* TODO: replace me with a sleep_on */
 124                                 continue;
 125                         }
 126                 }
 127
 128                 /* Read from cur to tail */
 129 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 130                 len_first_part = len_total = shbuf_tail - cur;
 131                 if (len_total < 0) {
 132                         /* message wraps: */
 133                         /* [SECOND PART.........FIRST PART] */
 134                         /*  ^data      ^tail    ^cur      ^size */
 135                         len_total += shbuf_size;
 136                 }
 137                 copy = xmalloc(len_total + 1);
 138                 if (len_first_part < 0) {
 139                         /* message wraps (see above) */
 140                         len_first_part = shbuf_size - cur;
 141                         memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
 142                 }
 143                 memcpy(copy, shbuf_data + cur, len_first_part);
 144                 copy[len_total] = '\0';
 145                 cur = shbuf_tail;
 146 #else
 147                 while (cur != shbuf_tail) {
 148                         fputs(shbuf_data + cur, stdout);
 149                         cur += strlen(shbuf_data + cur) + 1;
 150                         if (cur >= shbuf_size)
 151                                 cur = 0;
 152                 }
 153 #endif
 154  unlock:
 155                 /* release the lock on the log chain */
 156                 sem_up(log_semid);
 157
 158 #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 159                 for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
 160                         fputs(copy + i, stdout);
 161                 }
 162                 free(copy);
 163 #endif
 164         } while (follow);
 165
 166         shmdt(shbuf);
 167
 168         fflush_stdout_and_exit(EXIT_SUCCESS);
 169 }