Re: [RFC/PATCH] usb-storage: wait for device scanning before mountingroot

[Stefan Richter]

Alan Stern wrote:
> New USB devices can appear at any time.  None are present when the 
> system is started; they are all detected dynamically by the khubd 
> thread.
> 
> While I'm not familiar with the details of any other hotpluggable 
> buses (like Firewire), I imagine much the same is true for them.

It's very similar with FireWire.  FireWire devices announce SBP-2 target
capability (if they have it) after they became ready.  The ieee1394 or
firewire core then scans or re-scans them in a process context.  Then
upper layer drivers like the SBP-2 driver are matched, bound, probed.

If SBP-2 targets went through a power state change, they typically first
power everything up (spin up media etc.) before they announce their
protocol capabilities, and this may of course take a while.  Before that
they just are inaccessible, and it is unknown whether they could become
candidates for access by upper layer drivers.
-- 
Stefan Richter
-=====-==--- -==- =-=--
http://arcgraph.de/sr/
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