把busybox 的logread 命令的源文件改成可单独编译

/* vi: set sw=4 ts=4: */
/*
 * circular buffer syslog implementation for busybox
 *
 * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
 *
 * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
 *
 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
 */

//#include "../include/libbb.h"
#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#include <sys/shm.h>
#include <ctype.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <netdb.h>
#include <setjmp.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stddef.h>
#include <string.h>
#include <sys/poll.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <termios.h>
#include <time.h>
#include <unistd.h>
#include <sys/param.h>

#define DEBUG 0

char bb_common_bufsiz1[2048];

/* our shared key (syslogd.c and logread.c must be in sync) */
enum { KEY_ID = 0x414e4547 }; /* "GENA" */

struct shbuf_ds {
 int32_t size;           // size of data - 1
 int32_t tail;           // end of message list
 char data[1];           // messages
};

static const struct sembuf init_sem[3] = {
 {0, -1, IPC_NOWAIT | SEM_UNDO},
 {1, 0}, {0, +1, SEM_UNDO}
};

struct globals {
 struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
 struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
 struct shbuf_ds *shbuf;
} FIX_ALIASING;
#define G (*(struct globals*)&bb_common_bufsiz1)
#define SMrup (G.SMrup)
#define SMrdn (G.SMrdn)
#define shbuf (G.shbuf)
#define INIT_G() do { \
 memcpy(SMrup, init_sem, sizeof(init_sem)); \
} while (0)

static void error_exit(const char *str)
{
 //release all acquired resources
 shmdt(shbuf);
 //bb_perror_msg_and_die(str);
}

/*
 * sem_up - up()'s a semaphore.
 */
static void sem_up(int semid)
{
 if (semop(semid, SMrup, 1) == -1)
  error_exit("semop[SMrup]");
}

static void interrupted(int sig )
{
 signal(SIGINT, SIG_IGN);
 shmdt(shbuf);
 exit(EXIT_SUCCESS);
}

int main(int argc , char **argv)
{
 unsigned cur;
 int log_semid; /* ipc semaphore id */
 int log_shmid; /* ipc shared memory id */
 char follow = 1;//getopt32(argv, "f");

 INIT_G();

 log_shmid = shmget(KEY_ID, 0, 0);
 if (log_shmid == -1)
 {;}// bb_perror_msg_and_die("can't find syslogd buffer");

 /* Attach shared memory to our char* */
 shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
 if (shbuf == NULL)
 {;} // bb_perror_msg_and_die("can't access syslogd buffer");

 log_semid = semget(KEY_ID, 0, 0);
 if (log_semid == -1)
  error_exit("can't get access to semaphores for syslogd buffer");

 signal(SIGINT, interrupted);

 /* Suppose atomic memory read */
 /* Max possible value for tail is shbuf->size - 1 */
 cur = shbuf->tail;

 /* Loop for logread -f, one pass if there was no -f */
 do {
  unsigned shbuf_size;
  unsigned shbuf_tail;
  const char *shbuf_data;
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
  int i;
  int len_first_part;
  int len_total = len_total; /* for gcc */
  char *copy = copy; /* for gcc */
#endif
  if (semop(log_semid, SMrdn, 2) == -1)
   error_exit("semop[SMrdn]");

  /* Copy the info, helps gcc to realize that it doesn't change */
  shbuf_size = shbuf->size;
  shbuf_tail = shbuf->tail;
  shbuf_data = shbuf->data; /* pointer! */

  if (DEBUG)
   printf("cur:%d tail:%i size:%i\n",
     cur, shbuf_tail, shbuf_size);

  if (!follow) {
   /* advance to oldest complete message */
   /* find NUL */
   cur += strlen(shbuf_data + cur);
   if (cur >= shbuf_size) { /* last byte in buffer? */
    cur = strnlen(shbuf_data, shbuf_tail);
    if (cur == shbuf_tail)
     goto unlock; /* no complete messages */
   }
   /* advance to first byte of the message */
   cur++;
   if (cur >= shbuf_size) /* last byte in buffer? */
    cur = 0;
  } else { /* logread -f */
   if (cur == shbuf_tail) {
    sem_up(log_semid);
    fflush(NULL);
    sleep(1); /* TODO: replace me with a sleep_on */
    continue;
   }
  }

  /* Read from cur to tail */
#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
  len_first_part = len_total = shbuf_tail - cur;
  if (len_total < 0) {
   /* message wraps: */
   /* [SECOND PART.........FIRST PART] */
   /*  ^data      ^tail    ^cur      ^size */
   len_total += shbuf_size;
  }
  copy = xmalloc(len_total + 1);
  if (len_first_part < 0) {
   /* message wraps (see above) */
   len_first_part = shbuf_size - cur;
   memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
  }
  memcpy(copy, shbuf_data + cur, len_first_part);
  copy[len_total] = '\0';
  cur = shbuf_tail;
#else
  while (cur != shbuf_tail) {
   fputs(shbuf_data + cur, stdout);
   cur += strlen(shbuf_data + cur) + 1;
   if (cur >= shbuf_size)
    cur = 0;
  }
#endif
 unlock:
  /* release the lock on the log chain */
  sem_up(log_semid);

#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
  for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
   fputs(copy + i, stdout);
  }
  free(copy);
#endif
 } while (follow);

 shmdt(shbuf);

 //fflush_stdout_and_exit(EXIT_SUCCESS);
}