That failure mode is pretty uncommon. More often what happens is the
connection remains intact but communication/protocol/firmware/???
errors cause the device to stop working. It never disappears but it
can't be used again without unplugging or power-cycling.
Yes.
The difficulty here is that this "error" is indistinguishable from
normal activity -- someone simply unplugs the device and then later on
another connection is made. It might be the same device as before or
it might be a different one. In other words, it isn't really an error.
You would solve this by relying on "a few seconds" timeout.
Interesting. I've been working on something very much like your 1) for
some time. A version of it is now in the USB development tree. It's
not meant for situations like the one you describe; instead it is
intended for suspend-to-RAM or hibernation. Generally these processes
involve loss of power on the USB bus, causing it to appear as though
all the devices have been unplugged.
In theory the same approach could be used to recover connections even
in the absence of an intervening suspend. It would be clumsy in some
respects, though. For instance, when a device actually was
disconnected, the USB core wouldn't be able to notify the device's
driver for a few seconds. In that time lots of unwanted activity and
errors could mount up.
It also goes against the USB specification. And it is potentially
unsafe, in that it is possible for users to change media or make other
alterations that the kernel cannot detect. The same would be true of
your proposal, assuming that somebody was quick enough to unplug one
device and plug in another (or swap memory cards) in the span of a few
seconds.
Alan Stern
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