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

[Greg KH]

On Tue, Nov 12, 2013 at 07:54:42PM +1100, NeilBrown wrote:
> On Tue, 12 Nov 2013 00:10:28 -0800 Greg KH <gregkh at linuxfoundation.org> wrote:
> 
> > On Tue, Nov 12, 2013 at 11:31:45AM +1100, NeilBrown wrote:
> > > Alternately, is there some "all devices have been probed, nothing new will
> > > appear unless it is hot-plugged" event.  That would be equally useful (and
> > > probably mirrors what hardware-RAID cards do).
> > 
> > No, there's no way to ever know this in a hotplug world, sorry.
> > Especially with USB devices, they show up when they show up, there's no
> > "oh look, the bus is all scanned now and all devices currently plugged
> > in are found" type knowledge at all.
> > 
> > Then there are hotplug PCI systems where people slam in PCI cards
> > whenever they feel like it (remember, thunderbolt is PCI express...)
> > 
> > Sorry,
> > 
> > greg k-h
> 
> Surely something must be possible.

For USB, nope, there isn't, sorry.

> Clearly a physical hot-plug event will cause more devices to appear, but
> there must come a point at which no more (non-virtual) devices will appear
> unless a physical event happens?

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".

sorry,

greg k-h