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    SubjectRe: [Xen-devel][PATCH] xen/netfront: Remove unneeded .resume callback
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    On 3/14/19 11:10 AM, Oleksandr Andrushchenko wrote:
    > On 3/14/19 5:02 PM, Boris Ostrovsky wrote:
    >> On 3/14/19 10:52 AM, Oleksandr Andrushchenko wrote:
    >>> On 3/14/19 4:47 PM, Boris Ostrovsky wrote:
    >>>> On 3/14/19 9:17 AM, Oleksandr Andrushchenko wrote:
    >>>>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
    >>>>>
    >>>>> Currently on driver resume we remove all the network queues and
    >>>>> destroy shared Tx/Rx rings leaving the driver in its current state
    >>>>> and never signaling the backend of this frontend's state change.
    >>>>> This leads to the number of consequences:
    >>>>> - when frontend withdraws granted references to the rings etc. it
    >>>>> cannot
    >>>>>     be cleanly done as the backend still holds those (it was not
    >>>>> told to
    >>>>>     free the resources)
    >>>>> - it is not possible to resume driver operation as all the
    >>>>> communication
    >>>>>     means with the backned were destroyed by the frontend, thus
    >>>>>     making the frontend appear to the guest OS as functional, but
    >>>>>     not really.
    >>>> What do you mean? Are you saying that after resume you lose
    >>>> connectivity?
    >>> Exactly, if you take a look at the .resume callback as it is now
    >>> what it does it destroys the rings etc. and never notifies the backend
    >>> of that, e.g. it stays in, say, connected state with communication
    >>> channels destroyed. It never goes into any other Xen bus state, so
    >>> there is
    >>> no way its state machine can help recovering.
    >>
    >> My tree is about a month old so perhaps there is some sort of regression
    >> but this certainly works for me. After resume netfront gets
    >> XenbusStateInitWait from backend which causes xennet_connect().
    > Ah, the difference can be of the way we get the guest enter
    > the suspend state. I am making my guest to suspend with:
    > echo mem > /sys/power/state
    > And then I use an interrupt to the guest (this is a test code)
    > to wake it up.
    > Could you please share your exact use-case when the guest enters suspend
    > and what you do to resume it?


    xl save / xl restore

    > I can see no way backend may want enter XenbusStateInitWait in my
    > use-case
    > as it simply doesn't know we want him to.


    Yours looks like ACPI path, I don't know how well it was tested TBH.


    -boris

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