mirror of
https://github.com/sheumann/hush.git
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186 lines
4.5 KiB
C
186 lines
4.5 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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/* our shared key (syslogd.c and logread.c must be in sync) */
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enum { KEY_ID = 0x414e4547 }; /* "GENA" */
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struct shbuf_ds {
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int32_t size; // size of data - 1
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int32_t tail; // end of message list
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char data[1]; // messages
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};
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static const struct sembuf init_sem[3] = {
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{0, -1, IPC_NOWAIT | SEM_UNDO},
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{1, 0}, {0, +1, SEM_UNDO}
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};
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struct globals {
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struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO},
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struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO}
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struct shbuf_ds *shbuf;
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} FIX_ALIASING;
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#define G (*(struct globals*)&bb_common_bufsiz1)
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#define SMrup (G.SMrup)
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#define SMrdn (G.SMrdn)
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#define shbuf (G.shbuf)
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#define INIT_G() do { \
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memcpy(SMrup, init_sem, sizeof(init_sem)); \
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} while (0)
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static void error_exit(const char *str) 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(shbuf);
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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 UNUSED_PARAM)
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{
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signal(SIGINT, SIG_IGN);
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shmdt(shbuf);
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exit(EXIT_SUCCESS);
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}
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int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int logread_main(int argc UNUSED_PARAM, char **argv)
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{
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unsigned 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(argv, "f");
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INIT_G();
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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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shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
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if (shbuf == 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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signal(SIGINT, interrupted);
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/* Suppose atomic memory read */
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/* Max possible value for tail is shbuf->size - 1 */
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cur = shbuf->tail;
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/* Loop for logread -f, one pass if there was no -f */
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do {
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unsigned shbuf_size;
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unsigned shbuf_tail;
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const char *shbuf_data;
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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int i;
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int len_first_part;
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int len_total = len_total; /* for gcc */
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char *copy = copy; /* for gcc */
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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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/* Copy the info, helps gcc to realize that it doesn't change */
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shbuf_size = shbuf->size;
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shbuf_tail = shbuf->tail;
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shbuf_data = shbuf->data; /* pointer! */
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if (DEBUG)
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printf("cur:%d tail:%i size:%i\n",
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cur, shbuf_tail, shbuf_size);
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if (!follow) {
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/* advance to oldest complete message */
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/* find NUL */
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cur += strlen(shbuf_data + cur);
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if (cur >= shbuf_size) { /* last byte in buffer? */
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cur = strnlen(shbuf_data, shbuf_tail);
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if (cur == shbuf_tail)
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goto unlock; /* no complete messages */
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}
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/* advance to first byte of the message */
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cur++;
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if (cur >= shbuf_size) /* last byte in buffer? */
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cur = 0;
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} else { /* logread -f */
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if (cur == shbuf_tail) {
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sem_up(log_semid);
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fflush_all();
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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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}
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/* Read from cur to tail */
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#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
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len_first_part = len_total = shbuf_tail - cur;
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if (len_total < 0) {
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/* message wraps: */
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/* [SECOND PART.........FIRST PART] */
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/* ^data ^tail ^cur ^size */
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len_total += shbuf_size;
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}
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copy = xmalloc(len_total + 1);
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if (len_first_part < 0) {
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/* message wraps (see above) */
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len_first_part = shbuf_size - cur;
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memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
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}
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memcpy(copy, shbuf_data + cur, len_first_part);
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copy[len_total] = '\0';
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cur = shbuf_tail;
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#else
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while (cur != shbuf_tail) {
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fputs(shbuf_data + cur, stdout);
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cur += strlen(shbuf_data + cur) + 1;
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if (cur >= shbuf_size)
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cur = 0;
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}
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#endif
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unlock:
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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 (i = 0; i < len_total; i += strlen(copy + i) + 1) {
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fputs(copy + i, stdout);
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}
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free(copy);
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#endif
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} while (follow);
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shmdt(shbuf);
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fflush_stdout_and_exit(EXIT_SUCCESS);
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}
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