[BusyBox] Re: busybox-cvs Digest, Vol 29, Issue 4

[Rainer Weikusat]

"Vladimir N. Oleynik" <dzo at simtreas.ru> writes:
> pgf,
>
> What for you commiting all patches successively?
>
>
>> +		/* there is no way for bb_getopt_ulflags() to
>> +		 * return us the argument string for long options
>> +		 * which don't have a short option equivalent.
>
> Its False. Have way: using non printable short option.
>
>> commiting:
>>     0000073: Add option to inetd applet to run in foreground
>> this option was already there for uclinux -- this just exposes
>> it in the normal case as well.
>
> Idioten patch. Absolytelly unecessary.

What actually is unecessary is that each and every program contains a
virtually identical sequence of code to turn it into a background
process, especially given that there is at least one program that
always runs in the background, namely, init, and which already
contains everything required to be a 'supervisor' process. For special
tasks that should run in the background, a tool can be used to just
start them that way (please note that the code below needs
POSIXLY_CORRECT=1 in the environment, to work around serious GNU
getopt braindamage, and that it contains some features that are specific
to the enviroment it usually operates in).

-------------------------------
/*
  run a program in a background session
*/
char const eli_daemon_rscid[] = "$Id: daemon.c,v 1.6 2005/07/14 10:46:51 rw Exp $";

/*  includes */
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>

#include <eli.h>

/*  macros */
#define LOCK_PREFIX		"\x1nlock-"	/* also defined in nlock.c */
#define LOCK_PREFIX_LEN		(sizeof(LOCK_PREFIX) - 1)

/*  variables */
extern char **environ;

static int close_fds;

/*  functions */
static int sys_die(char const *fnc, char const *sysc) __attribute__ ((noreturn));

static int sys_die(char const *fnc, char const *sysc)
{
    syslog(LOG_ERR, "%s: %s: %m(%d)", fnc, sysc, errno);
    exit(1);
}

static void usage(void)
{
    syslog(LOG_NOTICE, "Usage: daemon [-c] [-f] <program> <arg> ...");
    syslog(LOG_NOTICE, "    c    -    remove lock parameters from environment");
    syslog(LOG_NOTICE, "    f    -    close descriptors except 0, 1, and 2");
    exit(1);
}

static void remove_lock_params(void)
{
    char **e_run, **e_last;

    e_last = e_run = environ;
    if (!*e_last) return;
    while (e_last[1]) ++e_last;
    
    e_run = environ;
    while (e_run < e_last)
	if (strncmp(*e_run, LOCK_PREFIX, LOCK_PREFIX_LEN) == 0) {
	    *e_run = *e_last;
	    *e_last-- = NULL;
	} else
	    ++e_run;
    
    if (strncmp(*e_run, LOCK_PREFIX, LOCK_PREFIX_LEN) == 0) *e_run = NULL;
}

static char **parse_args(int argc, char **argv)
{
    int c, had_c;

    had_c = 0;
    while ((c = getopt(argc, argv, "cf?h")) != -1)
	switch (c) {
	case 'c':
	    if (!had_c) remove_lock_params();
	    had_c = 1;
	    break;

	case 'f':
	    close_fds = 1;
	    break;

	case 'h':
	case '?':
	    usage();
	}

    return argv + optind;
}

/*  main */
int main(int argc, char **argv)
{
    static int fds_to_pass[] = {
	0, 1, 2, -1
    };

    char **cmdv;
    int rc, is_std_fd;

    openlog("daemon", LOG_PID | LOG_CONS | LOG_PERROR, LOG_DAEMON);
    
    if (argc < 2) usage();

    cmdv = parse_args(argc, argv);
    
    rc = fork();
    switch (rc) {
    case -1:
	sys_die(__FUNCTION__, "fork");

    case 0:
	break;

    default:
	_exit(0);
    }

    setsid();
    signal(SIGHUP, SIG_IGN);
    signal(SIGINT, SIG_IGN);
    signal(SIGQUIT, SIG_IGN);

    rc = open("/dev/null", O_RDWR, 0);
    rc != -1 || sys_die(__FUNCTION__, "open");

    is_std_fd = 0;
    if (rc != 0) dup2(rc, 0);
    else is_std_fd = 1;
    if (rc != 1) dup2(rc, 1);
    else is_std_fd = 1;
    if (rc != 2) dup2(rc, 2);
    else is_std_fd = 1;
    if (!is_std_fd) close(rc);

    if (close_fds) eli_close_unneeded_fds(fds_to_pass);
    execvp(*cmdv, cmdv);
    sys_die(__FUNCTION__, "execvp");
    return 0;
}