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
  13 #include "busybox.h"
  14 #include <stdio.h>
  15 #include <stdlib.h>
  16 #include <string.h>
  17 #include <sys/ipc.h>
  18 #include <sys/types.h>
  19 #include <sys/sem.h>
  20 #include <sys/shm.h>
  21 #include <signal.h>
  22 #include <setjmp.h>
  23 #include <unistd.h>
  24
  25 static const long KEY_ID = 0x414e4547; /*"GENA"*/
  26
  27 static struct shbuf_ds {
  28         int size;               // size of data written
  29         int head;               // start of message list
  30         int tail;               // end of message list
  31         char data[1];           // data/messages
  32 } *buf = NULL;                  // shared memory pointer
  33
  34
  35 // Semaphore operation structures
  36 static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
  37 static struct sembuf SMrdn[2] = {{1, 0}, {0, +1, SEM_UNDO}}; // set SMrdn
  38
  39 static int      log_shmid = -1; // ipc shared memory id
  40 static int      log_semid = -1; // ipc semaphore id
  41 static jmp_buf  jmp_env;
  42
  43 static void error_exit(const char *str);
  44 static void interrupted(int sig);
  45
  46 /*
  47  * sem_up - up()'s a semaphore.
  48  */
  49 static inline void sem_up(int semid)
  50 {
  51         if ( semop(semid, SMrup, 1) == -1 )
  52                 error_exit("semop[SMrup]");
  53 }
  54
  55 /*
  56  * sem_down - down()'s a semaphore
  57  */
  58 static inline void sem_down(int semid)
  59 {
  60         if ( semop(semid, SMrdn, 2) == -1 )
  61                 error_exit("semop[SMrdn]");
  62 }
  63
  64 int logread_main(int argc, char **argv)
  65 {
  66         int i;
  67         int follow=0;
  68
  69         if (argc == 2 && argv[1][0]=='-' && argv[1][1]=='f') {
  70                 follow = 1;
  71         } else {
  72                 /* no options, no getopt */
  73                 if (argc > 1)
  74                         bb_show_usage();
  75         }
  76
  77         // handle interrupt signal
  78         if (setjmp(jmp_env)) goto output_end;
  79
  80         // attempt to redefine ^C signal
  81         signal(SIGINT, interrupted);
  82
  83         if ( (log_shmid = shmget(KEY_ID, 0, 0)) == -1)
  84                 error_exit("Can't find circular buffer");
  85
  86         // Attach shared memory to our char*
  87         if ( (buf = shmat(log_shmid, NULL, SHM_RDONLY)) == NULL)
  88                 error_exit("Can't get access to circular buffer from syslogd");
  89
  90         if ( (log_semid = semget(KEY_ID, 0, 0)) == -1)
  91                 error_exit("Can't get access to semaphone(s) for circular buffer from syslogd");
  92
  93         // Suppose atomic memory move
  94         i = follow ? buf->tail : buf->head;
  95
  96         do {
  97 #ifdef CONFIG_FEATURE_LOGREAD_REDUCED_LOCKING
  98                 char *buf_data;
  99                 int log_len,j;
 100 #endif
 101
 102                 sem_down(log_semid);
 103
 104                 //printf("head: %i tail: %i size: %i\n",buf->head,buf->tail,buf->size);
 105                 if (buf->head == buf->tail || i==buf->tail) {
 106                         if (follow) {
 107                                 sem_up(log_semid);
 108                                 sleep(1);       /* TODO: replace me with a sleep_on */
 109                                 continue;
 110                         } else {
 111                                 printf("<empty syslog>\n");
 112                         }
 113                 }
 114
 115                 // Read Memory
 116 #ifdef CONFIG_FEATURE_LOGREAD_REDUCED_LOCKING
 117                 log_len = buf->tail - i;
 118                 if (log_len < 0)
 119                         log_len += buf->size;
 120                 buf_data = (char *)xmalloc(log_len);
 121
 122                 if (buf->tail < i) {
 123                         memcpy(buf_data, buf->data+i, buf->size-i);
 124                         memcpy(buf_data+buf->size-i, buf->data, buf->tail);
 125                 } else {
 126                         memcpy(buf_data, buf->data+i, buf->tail-i);
 127                 }
 128                 i = buf->tail;
 129
 130 #else
 131                 while ( i != buf->tail) {
 132                         printf("%s", buf->data+i);
 133                         i+= strlen(buf->data+i) + 1;
 134                         if (i >= buf->size )
 135                                 i=0;
 136                 }
 137 #endif
 138                 // release the lock on the log chain
 139                 sem_up(log_semid);
 140
 141 #ifdef CONFIG_FEATURE_LOGREAD_REDUCED_LOCKING
 142                 for (j=0; j < log_len; j+=strlen(buf_data+j)+1) {
 143                         printf("%s", buf_data+j);
 144                         if (follow)
 145                                 fflush(stdout);
 146                 }
 147                 free(buf_data);
 148 #endif
 149                 fflush(stdout);
 150         } while (follow);
 151
 152 output_end:
 153         if (log_shmid != -1)
 154                 shmdt(buf);
 155
 156         return EXIT_SUCCESS;
 157 }
 158
 159 static void interrupted(int sig){
 160         signal(SIGINT, SIG_IGN);
 161         longjmp(jmp_env, 1);
 162 }
 163
 164 static void error_exit(const char *str){
 165         bb_perror_msg(str);
 166         //release all acquired resources
 167         if (log_shmid != -1)
 168                 shmdt(buf);
 169
 170         exit(1);
 171 }