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 source tree.
  10 */
  11
  12//usage:#define logread_trivial_usage
  13//usage:       "[-fF]"
  14//usage:#define logread_full_usage "\n\n"
  15//usage:       "Show messages in syslogd's circular buffer\n"
  16//usage:     "\n        -f      Output data as log grows"
  17//usage:     "\n        -F      Same as -f, but dump buffer first"
  18
  19#include "libbb.h"
  20#include <sys/ipc.h>
  21#include <sys/sem.h>
  22#include <sys/shm.h>
  23
  24#define DEBUG 0
  25
  26/* our shared key (syslogd.c and logread.c must be in sync) */
  27enum { KEY_ID = 0x414e4547 }; /* "GENA" */
  28
  29struct shbuf_ds {
  30        int32_t size;           // size of data - 1
  31        int32_t tail;           // end of message list
  32        char data[1];           // messages
  33};
  34
  35static const struct sembuf init_sem[3] = {
  36        {0, -1, IPC_NOWAIT | SEM_UNDO},
  37        {1, 0}, {0, +1, SEM_UNDO}
  38};
  39
  40struct globals {
  41        struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
  42        struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
  43        struct shbuf_ds *shbuf;
  44} FIX_ALIASING;
  45#define G (*(struct globals*)&bb_common_bufsiz1)
  46#define SMrup (G.SMrup)
  47#define SMrdn (G.SMrdn)
  48#define shbuf (G.shbuf)
  49#define INIT_G() do { \
  50        memcpy(SMrup, init_sem, sizeof(init_sem)); \
  51} while (0)
  52
  53#if 0
  54static void error_exit(const char *str) NORETURN;
  55static void error_exit(const char *str)
  56{
  57        /* Release all acquired resources */
  58        shmdt(shbuf);
  59        bb_perror_msg_and_die(str);
  60}
  61#else
  62/* On Linux, shmdt is not mandatory on exit */
  63# define error_exit(str) bb_perror_msg_and_die(str)
  64#endif
  65
  66/*
  67 * sem_up - up()'s a semaphore.
  68 */
  69static void sem_up(int semid)
  70{
  71        if (semop(semid, SMrup, 1) == -1)
  72                error_exit("semop[SMrup]");
  73}
  74
  75static void interrupted(int sig)
  76{
  77        /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */
  78        kill_myself_with_sig(sig);
  79}
  80
  81int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  82int logread_main(int argc UNUSED_PARAM, char **argv)
  83{
  84        unsigned cur;
  85        int log_semid; /* ipc semaphore id */
  86        int log_shmid; /* ipc shared memory id */
  87        int follow = getopt32(argv, "fF");
  88
  89        INIT_G();
  90
  91        log_shmid = shmget(KEY_ID, 0, 0);
  92        if (log_shmid == -1)
  93                bb_perror_msg_and_die("can't %s syslogd buffer", "find");
  94
  95        /* Attach shared memory to our char* */
  96        shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
  97        if (shbuf == NULL)
  98                bb_perror_msg_and_die("can't %s syslogd buffer", "access");
  99
 100        log_semid = semget(KEY_ID, 0, 0);
 101        if (log_semid == -1)
 102                error_exit("can't get access to semaphores for syslogd buffer");
 103
 104        bb_signals(BB_FATAL_SIGS, interrupted);
 105
 106        /* Suppose atomic memory read */
 107        /* Max possible value for tail is shbuf->size - 1 */
 108        cur = shbuf->tail;
 109
 110        /* Loop for -f or -F, one pass otherwise */
 111        do {
 112                unsigned shbuf_size;
 113                unsigned shbuf_tail;
 114                const char *shbuf_data;
 115#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 116                int i;
 117                int len_first_part;
 118                int len_total = len_total; /* for gcc */
 119                char *copy = copy; /* for gcc */
 120#endif
 121                if (semop(log_semid, SMrdn, 2) == -1)
 122                        error_exit("semop[SMrdn]");
 123
 124                /* Copy the info, helps gcc to realize that it doesn't change */
 125                shbuf_size = shbuf->size;
 126                shbuf_tail = shbuf->tail;
 127                shbuf_data = shbuf->data; /* pointer! */
 128
 129                if (DEBUG)
 130                        printf("cur:%u tail:%u size:%u\n",
 131                                        cur, shbuf_tail, shbuf_size);
 132
 133                if (!(follow & 1)) { /* not -f */
 134                        /* if -F, "convert" it to -f, so that we dont
 135                         * dump the entire buffer on each iteration
 136                         */
 137                        follow >>= 1;
 138
 139                        /* advance to oldest complete message */
 140                        /* find NUL */
 141                        cur += strlen(shbuf_data + cur);
 142                        if (cur >= shbuf_size) { /* last byte in buffer? */
 143                                cur = strnlen(shbuf_data, shbuf_tail);
 144                                if (cur == shbuf_tail)
 145                                        goto unlock; /* no complete messages */
 146                        }
 147                        /* advance to first byte of the message */
 148                        cur++;
 149                        if (cur >= shbuf_size) /* last byte in buffer? */
 150                                cur = 0;
 151                } else { /* -f */
 152                        if (cur == shbuf_tail) {
 153                                sem_up(log_semid);
 154                                fflush_all();
 155                                sleep(1); /* TODO: replace me with a sleep_on */
 156                                continue;
 157                        }
 158                }
 159
 160                /* Read from cur to tail */
 161#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 162                len_first_part = len_total = shbuf_tail - cur;
 163                if (len_total < 0) {
 164                        /* message wraps: */
 165                        /* [SECOND PART.........FIRST PART] */
 166                        /*  ^data      ^tail    ^cur      ^size */
 167                        len_total += shbuf_size;
 168                }
 169                copy = xmalloc(len_total + 1);
 170                if (len_first_part < 0) {
 171                        /* message wraps (see above) */
 172                        len_first_part = shbuf_size - cur;
 173                        memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
 174                }
 175                memcpy(copy, shbuf_data + cur, len_first_part);
 176                copy[len_total] = '\0';
 177                cur = shbuf_tail;
 178#else
 179                while (cur != shbuf_tail) {
 180                        fputs(shbuf_data + cur, stdout);
 181                        cur += strlen(shbuf_data + cur) + 1;
 182                        if (cur >= shbuf_size)
 183                                cur = 0;
 184                }
 185#endif
 186 unlock:
 187                /* release the lock on the log chain */
 188                sem_up(log_semid);
 189
 190#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
 191                for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
 192                        fputs(copy + i, stdout);
 193                }
 194                free(copy);
 195#endif
 196                fflush_all();
 197        } while (follow);
 198
 199        /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */
 200
 201        fflush_stdout_and_exit(EXIT_SUCCESS);
 202}
 203