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