LXR busybox/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) */
  20enum { KEY_ID = 0x414e4547 }; /* "GENA" */
  21
  22struct 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
  28static const struct sembuf init_sem[3] = {
  29        {0, -1, IPC_NOWAIT | SEM_UNDO},
  30        {1, 0}, {0, +1, SEM_UNDO}
  31};
  32
  33struct 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
  46static void error_exit(const char *str) NORETURN;
  47static 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 */
  57static void sem_up(int semid)
  58{
  59        if (semop(semid, SMrup, 1) == -1)
  60                error_exit("semop[SMrup]");
  61}
  62
  63static void interrupted(int sig UNUSED_PARAM)
  64{
  65        signal(SIGINT, SIG_IGN);
  66        shmdt(shbuf);
  67        exit(EXIT_SUCCESS);
  68}
  69
  70int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  71int 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}
 186