[Yum-devel] [PATCH/RFC] What to do if a plugin fails to load?

[Tim Lauridsen]

James Antill wrote:
> On Wed, 2007-06-13 at 15:15 -0400, Jeremy Katz wrote:
>   
>> On Wed, 2007-06-13 at 14:52 -0400, Matthew Miller wrote:
>>     
>>> On Wed, Jun 13, 2007 at 02:43:13PM -0400, Jeremy Katz wrote:
>>>       
>>>> In some cases (especially on distro upgrades where you have to do
>>>> further updates after the fact), loading plugins can fail to load for
>>>> various reasons.  We should probably be tolerant of that and just not
>>>> load them.  What do people think of the attached?
>>>>         
>>> Not to make things more difficult, but some plugins may be more vital than
>>> others -- in some cases, running with a plugin disabled may really screw up
>>> the system. (For example, protectbase.) 
>>>       
>> Yeah, that's what makes things hard...  but blowing up with a traceback
>> of ImportError is almost certainly the wrong failure mode.
>>     
>
>  Personally, I can't think of any major cases[1] where a plugin is going
> to be so important that it's better to not run yum at all.
>  Even when you have edge cases like yum-security is broken, it's almost
> certainly better to have "yum --security update -y" do a full update in
> than to just fail and do nothing, even if it has a good error message.
>
>   
>>> How about making "failure mode" a
>>> standard configuration option in the conf file for each plugin?
>>>       
>> And then you get to "what if reading the conf file fails"?  
>>
>> Realistically, we just need to decide on a line and stick to it.  Either
>> a) Failure to load a plugin just disables the plugin
>> b) Failure to load a plugin aborts with a nice-ish error message
>>
>> My patch is the former, partially because it's the easier thing to
>> implement but also because getting out of the latter case is still not
>> obvious or simple for end-users.
>>     
>
>  The obvious candidate, for the second approach, would be something
> like:
>
>          try:
>              module = imp.load_module(modname, fp, pathname, description)
> +        except ImportError:
> +            raise PluginYumExit('"%s" plugin failed to load; use --noplugins' % modname)
>
> ...but as I said, I think your approach is better.
>
> [1] In theory it might be better to abort immediately, for query
> commands like: 
>
>   yum --security list updates
>
> ...which is done on the cmd line, but even then it's fairly easy to see
> what's gone wrong ... and someone running that from cron just before an
> update will likely disagree.
>
>   
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>   
My proposal is this one.

         try:
             module = imp.load_module(modname, fp, pathname, description)
        except ImportError:
            raise PluginYumExit('"%s" plugin failed to load; use --disableplugin' % modname)

--disableplugin=plugin name is a new feature added to current yum CVS Head.

The GUI's like pirut & yumex can catch the exception and ask the user what to do.
The CLI just bails out, with a message to the user to solve the issue. Maybe it should print the Stack trace so there is a way to
se what goes wrong in the plugin.

Tim




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