Re: [Xen-devel] [PATCH] qemu-stubdom: prevent useless medium change

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On 16/11/12 17:18, Ian Jackson wrote:
> Roger Pau Monne writes ("[Xen-devel] [PATCH] qemu-stubdom: prevent useless 
> medium change"):
>> qemu-stubdom was stripping the prefix from the "params" xenstore
>> key in xenstore_parse_domain_config, which was then saved stripped in
>> a variable. In xenstore_process_event we compare the "param" from
>> xenstore (not stripped) with the stripped "param" saved in the
>> variable, which leads to a medium change (even if there isn't any),
>> since we are comparing something like aio:/path/to/file with
>> /path/to/file. This only happens one time, since
>> xenstore_parse_domain_config is the only place where we strip the
>> prefix. The result of this bug is the following:
> 
> I have been thinking about this.
> 
> The reason I'm reluctant to apply this patch is that I'm worried it
> might cause some non-stubdom-related breakage.  I know it feels EBW,
> but perhaps the answer is _more_ #ifdef STUBDOM rather than less ?
> 
> Or do you think I should just read the code closely enough to
> understand it and your patch ?  I suspect it's a can of worms...

Yes, it's a can of worms indeed.

The non-stubdom path is not modified, and the code changes (1st block of
the patch) are contained inside a #ifdef STUBDOM (which is not seen on
the patch itself, because it's already there).

Thanks, Roger.


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