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Re: [libvirt] [PATCH libvirt v2 1/9] virConnectRegisterCloseCallback: Cleanup 'opaque' if there is no connectRegisterCloseCallback



On Wed, Jun 13, 2018 at 10:22 AM +0200, Marc Hartmayer <mhartmay linux ibm com> wrote:
> On Mon, Jun 04, 2018 at 06:25 PM +0200, "Daniel P. Berrangé" <berrange redhat com> wrote:
>> On Thu, Apr 26, 2018 at 08:16:54PM -0400, John Ferlan wrote:

[…snip…]

>>
>> If the application wants to access 'opaque' outside the context of the
>> callback function, it must take steps to ensure it is still alive in
>> whatever thread it using it. This implies the data passed for 'opaque'
>> should be ref-counted and they must hold a reference for their own
>> usage, separately from the reference assoicated with the callback that
>> will be released by @freecb.
>>
>> That all said, we could take a slightly different approach if we want
>> to be paranoid about this
>>
>> eg move the
>>
>>     virConnectCloseCallbackDataPtr closeCallback;
>>
>> out of the driver specific private structs, and put it in the main
>> struct _virConnect instead.
>
> This sound like a revert of commit “close callback: move it to driver”
> (88f09b75eb99415c). Shall we really do this?

Polite ping.

>
>>
>> The main libvirt-host.c can add the callback to this itself. THe
>> driver code only needs to worry about actually invoking the callback
>>
>> That would allow us to have freecb() called at the right time for
>> all drivers, even if they don't ever use the close callback.
>>
>>>
>>> I'm still not sure I understand why the API cannot return a failure, but
>>> Daniel says it cannot.
>>
>> It can break existing applications using hypervisors that don't
>> implement this API, becasue its a change in behaviour. In retrospect
>> I wouldn't have written the API in this way today, but we must live
>> with the design we have.
>>
>>
>> Regards,
>> Daniel
>> --
>> |: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
>> |: https://libvirt.org         -o-            https://fstop138.berrange.com :|
>> |: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|
>>
> --
> Beste Grüße / Kind regards
>    Marc Hartmayer
>
> IBM Deutschland Research & Development GmbH
> Vorsitzende des Aufsichtsrats: Martina Koederitz
> Geschäftsführung: Dirk Wittkopp
> Sitz der Gesellschaft: Böblingen
> Registergericht: Amtsgericht Stuttgart, HRB 243294
--
Beste Grüße / Kind regards
   Marc Hartmayer

IBM Deutschland Research & Development GmbH
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschäftsführung: Dirk Wittkopp
Sitz der Gesellschaft: Böblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294



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