Am Freitag, 7. Juni 2002 22:02 schrieb Scott Bronson:
> From the recent discussions it seems that there's some disagreement over
> exactly what device state should be preserved across suspend and
> resume. Is there a policy written down anywhere that tells what to do
> in situations like these?
No.
> For simple devices like mice and webcams, it's fine to just disconenct
> when suspending and re-enumerate on resume. Printers and scanners can
> be considered simple devices--I don't think it's reasonable to expect
> your printer to resume printing if you suspend your computer in the
> middle of a job.
For webcams it is not OK. All that it is OK for is printers and mice, IMHO.
> HOWEVER, all attached devices do need to keep their device nodes. They
> cannot re-order themselves arbitrarily while the machine is asleep.
> From my limited tests, it appears that this is currently the case. Is
> there code in place that guarantees this?
Yes and no.
Very recently the generic device model was finished.
Using it requires that the usb core does _not_ disconnect on suspend.
> What if I move my printer from one hub to another one while the machine
> is asleep? If I re-order devices, but don't plug any new ones in or
> out, should that cause device nodes to switch? I don't have any USB
> devices that share device nodes so I can't test this now.
>
>
> Network devices are a bit more complex because they need to keep
> connections across suspend and resume.
>
> PCMCIA does this currently, but it only does it if devices are NOT
> reordered while the machine is asleep. If I have multiple devices and I
> reorder them while the machine is asleep, they will often get bound to
> different interfaces (eth1 and eth0 will be swapped). Open connections
> are still associated with the old interface, so now they're associated
> with a different device. If I quickly swap them back, the connections
> still work fine. This might be an obscure security risk...?
In theory yes.
> Is this behavior acceptable for USB? If devices are re-ordered while
> the machine is asleep, then can it just enumerate the moved devices from
> scratch? That seems acceptable to me provided, of course, that all open
> connections are closed before associating an existing interface with a
> different device.
It most definitely is not. The camera in the bedroom must not switch
with the camera in the backyard.
> Is there any way to bind a specific network connection to a specific
> device, so that it doesn't matter what order I plug the device in or
> out, or move it, all connections follow it and wait for it to be plugged
> in again? This would be very useful for both PCMCIA and USB.
>
>
> Finally, problem of storage devices is very similar to that of network
> devices, isn't it? Mount points (/mnt/filestick) are like network
> interfaces (eth0). Open connections are like open files. Both
> interfaces and mount points need to be set up when the device is
> inserted.
>
> So, if the networking issues above are completely solved, then are the
> storage issues completely solved too?
Storage is different. It uses GUIDs and supports reattachment by itself.
Regards
Oliver
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