Re: [PATCH] Add setsid option to save child process id

On Wed, 2025-Jan-29, Karel Zak wrote:
> On Sun, Jan 26, 2025 at 10:40:19AM GMT, Marc Aurèle La France wrote:
>> Add an option to save the child's pid into a file.

>> @@ -105,6 +115,16 @@ int main(int argc, char **argv)
>>  			break;
>>  		default:
>>  			/* parent */
>> +			if (pidpath) {
>> +				pidfile = fopen(pidpath, "w");
>> +				if (pidfile == NULL)
>> +					warn(_("cannot open pidfile %s"),
>> +						pidpath);
>> +				else {
>> +					fprintf(pidfile, "%d\n", pid);
>> +					fclose(pidfile);
>> +				}
>> +			}
>>  			if (!status)
>>  				return EXIT_SUCCESS;
>>  			if (wait(&status) != pid)

> What is the intended use-case for this feature?

To put various utilities (ping, tcpdump, ad nauseam) in the background and
have a simple way of controlling each instance individually.

> I am unsure if this implementation is too simplistic. It seems that
> the file is not deleted after the child process exits. Furthermore,
> what would happen if we call multiple setsid instances with the same
> pidfile? Would it be better to create the pidfile in the child process
> after setsid() and ioctl(), in order to avoid creating the
> pidfile in case of an error?

> For reference, the code in misc-utils/uuidd.c uses a more advanced
> method.

Repeat after me:

KISS.

Marc.