Re: [PATCH v2] xtables: Add a smaller delay option when waiting for xtables lock

[subashab@codeaurora.org]

>> iptables -w 2.1
>> 
>> 0.01s sleep, retry
>> 0.02s sleep, retry
>> 0.03s sleep, retry
>> ...
>> 2.1s sleep, exit
>> 
>> Note that it sleeps for 10ms and retries rather than sleeping for a 
>> single
>> iteration for 2.1s seconds and then retrying.
>> 
>> Let me know if there are any concerns with this.
> 
> But this is changing the existing behaviour, right? My understanding
> is that -w indicates the net wait time for each try.

Hi Pablo

Currently, each wait time is 1 second. -w is the overall time upto which 
it has to wait.

bool xtables_lock(int wait)
{
	int fd, waited = 0, i = 0;

	fd = open(XT_LOCK_NAME, O_CREAT, 0600);
	if (fd < 0)
		return true;

	while (1) {
		if (flock(fd, LOCK_EX | LOCK_NB) == 0)
			return true;
		else if (wait >= 0 && waited >= wait)  //total time upto which we need 
to wait.
			return false;
		if (++i % 2 == 0)
			fprintf(stderr, "Another app is currently holding the xtables lock; "
				"waiting (%ds) for it to exit...\n", waited);
		waited++;
		sleep(1); //sleep for one second only
	}
}

My patch does not change the behavior of -w itself. It only changes the 
sleep interval to 10ms when a decimal is specified.
Existing behavior of 1 second sleep for integral interval is preserved.

--
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
Forum, a Linux Foundation Collaborative Project.