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Re: [Qemu-block] [RFC PATCH 6/6] pc: Support firmware configuration with


From: Laszlo Ersek
Subject: Re: [Qemu-block] [RFC PATCH 6/6] pc: Support firmware configuration with -blockdev
Date: Tue, 5 Mar 2019 18:08:11 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 03/04/19 18:50, Markus Armbruster wrote:

> Alright, we can call object_get_class(dev_obj)->unparent(dev_obj).
> 
> Final complication: if I call just that, the device's reference counter
> goes down to zero in the middle of device_unparent(), and we use after
> free.  So I bracket he call with object_ref() and object_unref().

I don't think that requiring such a bracketing is necessarily a problem.
I vaguely remember reviewing a kernel patch 6 or so years ago where the
patch used the same idea, with those "get" and "put" functions (the bug
the patch was fixing was that the last reference was "temporarily" lost
mid-operation).

So perhaps this can be addressed, for the general case, by extending the
documentation of device_unparent(). (The function has no documentation
at all, at the moment.)

Thanks
Laszlo



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