[systemd-devel] Need help with a systemd/mdadm interaction.

[NeilBrown]

On Tue, 12 Nov 2013 14:52:43 +0100 Zbigniew Jędrzejewski-Szmek
<zbyszek at in.waw.pl> wrote:

> On Tue, Nov 12, 2013 at 09:17:19PM +1100, NeilBrown wrote:
> > On Tue, 12 Nov 2013 18:16:24 +0900 Greg KH <gregkh at linuxfoundation.org> wrote:
> > > Not for USB, sorry.
> > > 
> > > The USB bus just announces devices when it finds them, there is no "all
> > > is quiet" type signal or detection.
> > > 
> > > Same for PCI hotplug, devices can show up at any point in time, you
> > > never know when, and you don't know when all devices are "found".
> > 
> > Hmmm... OK.  USB doesn't bother me a lot, but PCI is important.
> > 
> > I guess I'll just have to settle for a timeout much like the current
> > device-discovery timeout that systemd has.
> > Still hoping someone can tell me how to plug into that though...
> I think you'll have to replicate the waiting logic internally. udev
> will tell you about new devices, but systemd by itself doesn't know
> what devices are part of the raid set, so can't help with knowing
> when enough physical volumes have been found, either for degraded more
> or for normal mode. Just make sure to set your timeout to something
> lower than systemd, i.e. have timeout-waiting-for-normal-set <
> timeout-waiting-for-degraded-set < systemd-timeout-for-device.
> 
> Zbyszek

Internally to what?

Systemd knows  that it wants to mount a particular device.  It waits for it
and eventually times out.  At that point, when systemd has timed out, I want
it to tell me so I can try to make the device appear.  Systemd would then
need to check if the device actually has appeared and mount it if it has, or
fall back on the current failure handing if it hasn't.

Thanks,
NeilBrown
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