* Wen Congyang <we...@cn.fujitsu.com> [2011-03-08 23:09]: > At 03/09/2011 12:08 PM, Ryan Harper Write: > > * Wen Congyang <we...@cn.fujitsu.com> [2011-02-27 20:56]: > >> Hi Markus Armbruster > >> > >> At 02/23/2011 04:30 PM, Markus Armbruster Write: > >>> Isaku Yamahata <yamah...@valinux.co.jp> writes: > >>> > >> > >> <snip> > >> > >>> > >>> I don't think this patch is correct. Let me explain. > >>> > >>> Device hot unplug is *not* guaranteed to succeed. > >>> > >>> For some buses, such as USB, it always succeeds immediately, i.e. when > >>> the device_del monitor command finishes, the device is gone. Live is > >>> good. > >>> > >>> But for PCI, device_del merely initiates the ACPI unplug rain dance. It > >>> doesn't wait for the dance to complete. Why? The dance can take an > >>> unpredictable amount of time, including forever. > >>> > >>> Problem: Subsequent device_add can fail if it reuses the qdev ID or PCI > >>> slot, and the unplug has not yet completed (race condition), or it > >>> failed. Yes, Virginia, PCI hotplug *can* fail. > >>> > >>> When unplug succeeds, the qdev is automatically destroyed. > >>> pciej_write() does that for PIIX4. Looks like pcie_cap_slot_event() > >>> does it for PCIE. > >> > >> I got a similar problem. When I unplug a pci device by hand, it works > >> as expected, and I can hotplug it again. But when I use a srcipt to > >> do the same thing, sometimes it failed. I think I may find another bug. > >> > >> Steps to reproduce this bug: > >> 1. cat ./test-e1000.sh # RHEL6RC is domain name > >> #! /bin/bash > >> > >> while true; do > >> virsh attach-interface RHEL6RC network default --mac > >> 52:54:00:1f:db:c7 --model e1000 > >> if [[ $? -ne 0 ]]; then > >> break > >> fi > >> virsh detach-interface RHEL6RC network --mac 52:54:00:1f:db:c7 > >> if [[ $? -ne 0 ]]; then > >> break > >> fi > >> sleep 5 > > > > How do you know that the guest has responded at this point before you > > attempt to attach again at the top of the loop. Any attach/detach > > requires the guest to respond to the request and it may not respond at > > all. > > When I attach/detach interface by hand, it works fine: I can see the new > interface > when I attach it, and it disapears when I detached it.
The point is that since the attach and detach require guest participation, this interface isn't reliable. You have a sleep 5 in your loop, hoping to wait long enough for the guest to respond, but after a number of iterations in your loop it fails, you can bump the sleep to to 3600 seconds and the guest *still* might not respond... -- Ryan Harper Software Engineer; Linux Technology Center IBM Corp., Austin, Tx ry...@us.ibm.com
