Re: [Xen-devel] [PATCH V5 32/32] libxl: synchronize configuration when we plug / unplug device

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, May 20, 2014 at 04:33:45PM +0100, Ian Jackson wrote:
> Wei Liu writes ("[PATCH V5 32/32] libxl: synchronize configuration when we 
> plug / unplug device"):
> > This approach cannot deal with half-baked device state (say, if AO
> > returns success but for various reasons other parts just fail and we
> > have some xenstore entries written / resource allocated). However we
> > cannot make thing worse as the original code cannot handle that either.
> > The good side of this approach is that in the future we can compare the
> > stored configuration and xenstore entries to spot any half-baked device
> > state so it can help fix that issue in the future.
> 
> I'm still concerned about this.
> 
> And seeing the code which results from doing it this way hasn't really
> convinced me otherwise.  These macros are going to need to be adjusted
> again.
> 
> Wouldn't it be better to write something which can merge (a) the
> information currently obtained by libxl_device_disk_list,
> libxl__device_disk_from_xs_be et al and (b) the new JSON
> configuration ?
> 

This is certainly doable. But again, what's the desirable state to
record? If a device's entry is present in xenstore then it must be
valid? It might be my misundertanding of how we should handle half-baked
state. We shall have further discussion...

> Then you could arrange to add the device to the JSON config before
> doing anything else, and remove it afterwards, and then there would be
> no undesirable states etc.
> 

Sorry, it's unclear to me what you want me to do. Why do I need to
remove a device after I add it?

Wei.

> Ian.

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