busybox

/* 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.

 */

//config:config LOGREAD

//config:   bool "logread"

//config:   default y

//WRONG: it should be compilable without SYSLOG=y:

//WRONG:    depends on FEATURE_IPC_SYSLOG

//config:   help

//config:     If you enabled Circular Buffer support, you almost

//config:     certainly want to enable this feature as well. This

//config:     utility will allow you to read the messages that are

//config:     stored in the syslogd circular buffer.

//config:

//config:config FEATURE_LOGREAD_REDUCED_LOCKING

//config:   bool "Double buffering"

//config:   default y

//config:   depends on LOGREAD

//config:   help

//config:     'logread' ouput to slow serial terminals can have

//config:     side effects on syslog because of the semaphore.

//config:     This option make logread to double buffer copy

//config:     from circular buffer, minimizing semaphore

//config:     contention at some minor memory expense.

//config:

​

//applet:IF_LOGREAD(APPLET(logread, BB_DIR_SBIN, BB_SUID_DROP))

​

//kbuild:lib-$(CONFIG_LOGREAD) += logread.o

​

//usage:#define logread_trivial_usage

//usage:       "[-fF]"

//usage:#define logread_full_usage "\n\n"

//usage:       "Show messages in syslogd's circular buffer\n"

//usage:     "\n    -f  Output data as log grows"

//usage:     "\n    -F  Same as -f, but dump buffer first"

​

#include "libbb.h"

#include "common_bufsiz.h"

#include <sys/ipc.h>

#include <sys/sem.h>

#include <sys/shm.h>

​

#define DEBUG 0

​

/* 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},