the mechanism of USB hotplug

[kylin]

sir :
   I am now working on the pci e hotplug of freebsd ,and reading code
of the relative part in linux.
i have never touch the field of USB .
now i wonder the mechanism of USB hotplug and the scsi hotplug .
in linux and my working on freebsd ,there r specail mechanism to
waiting for the hotplug event ,and the IRQ and MEM IO resource
allocation is complex .
i am fresh to the USB and the even complex SCSI driver arch , could u
give me some advise ?
             thank u:)

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