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145 lines
3.3 KiB
C
145 lines
3.3 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* circular buffer syslog implementation for busybox
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*
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* Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
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*
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* Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
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*
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* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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*/
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#include "libbb.h"
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#include <sys/ipc.h>
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#include <sys/sem.h>
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#include <sys/shm.h>
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#define DEBUG 0
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enum { KEY_ID = 0x414e4547 }; /* "GENA" */
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static struct shbuf_ds {
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int32_t size; // size of data written
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int32_t head; // start of message list
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int32_t tail; // end of message list
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char data[1]; // data/messages
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} *buf; // shared memory pointer
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// Semaphore operation structures
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static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
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static struct sembuf SMrdn[2] = {{1, 0}, {0, +1, SEM_UNDO}}; // set SMrdn
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static void error_exit(const char *str) ATTRIBUTE_NORETURN;
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static void error_exit(const char *str)
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{
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//release all acquired resources
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shmdt(buf);
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bb_perror_msg_and_die(str);
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}
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/*
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* sem_up - up()'s a semaphore.
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*/
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static void sem_up(int semid)
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{
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if (semop(semid, SMrup, 1) == -1)
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error_exit("semop[SMrup]");
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}
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static void interrupted(int sig ATTRIBUTE_UNUSED)
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{
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signal(SIGINT, SIG_IGN);
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shmdt(buf);
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exit(0);
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}
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int logread_main(int argc, char **argv);
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int logread_main(int argc, char **argv)
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{
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int cur;
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int log_semid; /* ipc semaphore id */
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int log_shmid; /* ipc shared memory id */
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smallint follow = getopt32(argc, argv, "f");
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log_shmid = shmget(KEY_ID, 0, 0);
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if (log_shmid == -1)
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bb_perror_msg_and_die("can't find syslogd buffer");
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// Attach shared memory to our char*
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buf = shmat(log_shmid, NULL, SHM_RDONLY);
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if (buf == NULL)
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bb_perror_msg_and_die("can't access syslogd buffer");
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log_semid = semget(KEY_ID, 0, 0);
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if (log_semid == -1)
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error_exit("can't get access to semaphores for syslogd buffer");
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// attempt to redefine ^C signal
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signal(SIGINT, interrupted);
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// Suppose atomic memory move
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cur = follow ? buf->tail : buf->head;
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do {
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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char *buf_data;
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int log_len, j;
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#endif
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if (semop(log_semid, SMrdn, 2) == -1)
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error_exit("semop[SMrdn]");
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if (DEBUG)
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printf("head:%i cur:%d tail:%i size:%i\n",
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buf->head, cur, buf->tail, buf->size);
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if (buf->head == buf->tail || cur == buf->tail) {
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if (follow) {
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sem_up(log_semid);
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fflush(stdout);
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sleep(1); /* TODO: replace me with a sleep_on */
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continue;
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}
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puts("<empty syslog>");
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}
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// Read Memory
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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log_len = buf->tail - cur;
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if (log_len < 0)
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log_len += buf->size;
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buf_data = xmalloc(log_len);
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if (buf->tail >= cur)
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j = log_len;
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else
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j = buf->size - cur;
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memcpy(buf_data, buf->data + cur, j);
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if (buf->tail < cur)
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memcpy(buf_data + buf->size - cur, buf->data, buf->tail);
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cur = buf->tail;
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#else
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while (cur != buf->tail) {
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fputs(buf->data + cur, stdout);
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cur += strlen(buf->data + cur) + 1;
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if (cur >= buf->size)
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cur = 0;
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}
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#endif
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// release the lock on the log chain
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sem_up(log_semid);
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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for (j = 0; j < log_len; j += strlen(buf_data+j) + 1) {
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fputs(buf_data + j, stdout);
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}
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free(buf_data);
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#endif
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} while (follow);
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shmdt(buf);
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fflush_stdout_and_exit(EXIT_SUCCESS);
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}
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