Re: [Xen-devel] [PATCH] libxl: make libxl_cdrom_insert async

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Ian Campbell writes ("Re: [PATCH] libxl: make libxl_cdrom_insert async"):
> On Tue, 2012-07-24 at 17:49 +0100, Ian Jackson wrote:
> > This doesn't look actually /incorrect/ but I'm a bit suspicious: if
> > changing to a new non-empty disk, you first write params := "", in one
> > xenstore transaction, and then the non-empty value in a second
> > transaction.  Why ?
> 
> Mostly because xend did it that way, I agree that it seems pointless
> without adding any additional interlock to the protocol.
> 
> At one point I was hoping that copying xend closely would lead to
> working stubdom support etc, but that turned out to be a pipe dream.
> 
> Just writing the appropriate key once did seem to work, at least in the
> cases where it works at all, in my experiments so I guess I might as
> well change to that here.

If any other xenstore client depended on seeing the intermediate
value, the system would be buggy and it would only work by them
winning the race.  I guess it's possible that there would be a peer
with a strange bug which means that it misses the first watch event
but I think we should assume that there isn't unless we discover
otherwise.

Ian.

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