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Martyn Russell schreef op 12/05/2014 16:18:
> On 12/05/14 15:06, Ralph Böhme wrote:
>> Hi Martyn
[cut]
> We used to use DBus and that would instantiate processes for us,
> but now we have this "passive" approach. It has advantages and
> disadvantages.
It has mostly advantages in my opinion. Also wrt watchdogging.
Although we're no longer implementing it apparently ;) (which is a
problem)
> The advantage is, tracker-miner-fs is simpler and doesn't have to
> deal with the mess of broken files crashing tracker-extract and
> timeouts, etc. Also it means the file basic information is added to
> Tracker quicker than it was previously because we have no delay on
> tracker-extract. Another advantage half realised (bits can be
> improved still), is that we can group process files of the same
> time and prioritise files of particular types. We have mime type
> priorities currently I think. Disadvantages include having to wait
> for the second pass indexing to complete :)
>
> tracker-extract has _ALWAYS_ crashed because of the nature of the
> files and libraries we're using being the weakest point. With this
> in mind, it's quite bad that we don't have some sort of watchdog or
> way to keep it up and running.
I think the watchdog should be configurable per system configuration.
For example with systemd we can let systemd automatically manage (and
that includes restarting) the process in case of a crash.
On systems that don't use systemd they'll probably have another init
subsystem that can do managent of this.
I think that both for systemd-based and for those systems it would be
silly to insist on using our own implementation of a separate watchdog
or forever-loop script to ensure tracker-extract is kept up:
Often the sysadmin of such a system want the system-wide watchdog or
init infastructure to be aware of these restarts of the process.
Although I understand it smells like %windir%\system32\services.msc
and although the panic caused by this is becoming pandemic on
slashdot, I still think this is the right architecture nonetheless.
Because even our original implementation where tracker-extract was
activated because of a 'active' D-Bus method call was not perfect in
that there was no awareness or control by the system's infrastructure
to avoid that a constantly crashing tracker-extract is returning all
the times (what you later refer to as circular problems).
Except that miner-fs would in the original implementation after
several attempts skip the file causing the crash (which was, fair
enough, quite a good attempt at somewhat solving the situation).
Nonetheless should we outsource this logic to the init system or the
"CoreOS" infrastructure as Lennart calls it (the kid has a name now).
On a typical Linux in the future this will hopefully be systemd, and
in my opinion we only need to provide the hooks and configurability to
system integrators who plan to use a different system for this purpose
(with default implementations for systemd, and maybe also for upstart
and openrc or whatever popular-alternative init system the knigths who
say NI(H) will use).
An example reason why I think the Core-OS subsystem should do this is
because I also believe that tracker-extract should run in its own
lightweight container, precisely because it can crash (because a crash
on input like a file is often an indication of a serious security
problem -- a reason why it should run in a container in my opinion).
Infrastructure like systemd could in case of a tracker-extract crash
revert the copy-on-write filesystem behind the container and restart
the entire OS, or it could opt to just restart the tracker-extract
process. The strategy to use isn't something the Tracker project
should choose, but the init system could (based on the sysadmin's
choices).
> We could easily do this in tracker-miner-fs. Part of
But I think we shouldn't in case systemd is already doing it.
> me thinks we should actually have a tracker-control --daemon which
> watches all process and keeps some sort of journal / log going and
> also maintains processes like tracker-extract keep running. I
> should add, this is something that nearly EVERY embedded solution
> does itself with some script which keeps miner-fs running (not even
> tracker-extract), because there is no other way to guarantee
> Tracker is there to catch all events.
That script is what systemd should do.
> The only downsides I see are repeated attempts causing a circular
> problem with tracker-extract. But that's easily remedied, we had to
> do something like this in tracker-miner-fs before already.
Circular problems like this is what systemd would solve.
> Happy to help :)
Cheers :)
Philip
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