Xen devel - Mar 2009 - [PATCH] Make PyGrub run first entry in grub config when invalid default boot option provided

Hello everybody,
I have created a patch for pygrub and I am sending it as an attachment. 
This patch mainly solves the issue of invalid default boot option in 
VM''s configuration. If the entry doesn''t exist, it
doesn''t exit with
IndexError python exception but it uses first entry there to boot up the 
machine - same way like standard (real) grub does...

Signed-off-by: Michal Novotny <minovotn@redhat.com>


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Michal Novotny writes ("[Xen-devel] [PATCH] Make PyGrub run first entry in
grub config when invalid default boot option
provided"):
> -    img = g.cf.images[sel]
> +    try:
> +        img = g.cf.images[sel]
> +    except:
It is not correct to do this on all exceptions.  (This is a common
mistake in Python.)  I assume that in your error case the images array
doesn''t have the relevant entry and that your code should read:
  +        img = g.cf.images[sel]
  +    except KeyError:

Ian.

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Hi,
thanks for advice. Here''s new and corrected version of the patch. Well,
the error here is IndexError, when an error occurs so the IndexError is 
catched and not KeyError. I have also tried it with KeyError but it was 
not working so IndexError is catched here.

Michal

Ian Jackson wrote:
> Michal Novotny writes ("[Xen-devel] [PATCH] Make PyGrub run first
entry in grub config when invalid default boot option provided"):
>   
>> -    img = g.cf.images[sel]
>> +    try:
>> +        img = g.cf.images[sel]
>> +    except:
>>     
>
> It is not correct to do this on all exceptions.  (This is a common
> mistake in Python.)  I assume that in your error case the images array
> doesn''t have the relevant entry and that your code should read:
>   +        img = g.cf.images[sel]
>   +    except KeyError:
>
> Ian.
>   


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Michal Novotny writes ("Re: [Xen-devel] [PATCH] Make PyGrub run first entry
in grub config when invalid default boot option
provided"):
> thanks for advice. Here''s new and corrected version of the patch.
Well,
> the error here is IndexError, when an error occurs so the IndexError is 
> catched and not KeyError. I have also tried it with KeyError but it was 
> not working so IndexError is catched here.
Err, yes, I didn''t double-check with the docs or the rest of the
code.  Your version is very likely correct.

Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

Ian.

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