On Tue, 22 Sep 1998, James wrote:
->how do i write a daemon? I know what they are (little programs that do something
->useful in the background), but are they just normal programs that get pushed
->into the background?
->
Take a look at the c-programming FAQ available under
ftp://rtfm.mit.edu/pub/usenet-by-hierarchy/comp/lang/c
->and how do i monitor a /dev/TTYS? device so that when my modem picks up
->the line and connects to a remote computer my daemon does something, then
->when the modem puts down the line the daemon does something else?
->
U need to watch for the DCD line. Glynn Clements proposed once using the
TIOCMGET ioctl call and I find this quite useful. Something like this:
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <syslog.h>
#define SLEEP_INTERVAL 5
#define DCD_HIGH 1
#define DCD_LOW 0
extern char* program_invocation_short_name;
int TestDCD(int nDevice)
{
int nStatus;
if (ioctl(nDevice,TIOCMGET,&nStatus) == -1)
{
// oops something went wrong...
syslog(LOG_ERR,"ioctl error!\n");
exit(1);
}
else
return nStatus & TIOCM_CD;
}
int main(int argc,char** argv)
{
int fd;
openlog(program_invocation_short_name,0,LOG_DAEMON);
if (-1 == (fd = open( /*PUT THE TTYS DEVICE HERE*/ ,O_RDWR)))
{
syslog(LOG_ERR,"Canot open device\n");
exit(1);
};
while ( DCD_LOW == TestDCD(fd) )
sleep(SLEEP_INTERVAL);
/* here u have the DCD high i.e. modem connected */
/* do some stuff*/
while ( DCD_HIGH == TestDCD(fd) )
sleep(SLEEP_INTERVAL);
/* here the modems are already disconnected */
/* do other stuff */
closelog();
return 0;
}
U may consider installing SIGALARM handler.
Regards,
Marin
"Knowledge is not a crime. Some of its applications are..."
- Unknown hacker
