[virt-tools-list] virt-install: Add warn if 'single-use' options are defined multiple times?

[Cole Robinson]

On 10/04/2018 12:29 PM, Mark Kanda wrote:
> 
> 
> On 10/1/2018 12:16 PM, Cole Robinson wrote:
>> On 09/14/2018 04:28 PM, Mark Kanda wrote:
>>> Hi all,
>>>
>>> I recently discovered, for 'single-use' command line options, 
>>> virt-install silently ignores all but the last definition. For 
>>> example, if the command line has '--memory X' and later '--memory Y', 
>>> then 'X' is silently ignored.
>>>
>>> I think virt-install should warn the user if 'single use' options are 
>>> specified multiple times, and I'd like to implement a fix.
>>>
>>> However, before I implement such a fix, I'd like to know if this is 
>>> 'by design', or if anyone would otherwise object to such a check..
>>>
>>
>> Sorry for the late response. This isn't really intentional and more 
>> just a side effect of how our argparse options are initialized. I 
>> hacked up the attached diff that will essentially merge all ex. 
>> --memory options,
>> so --memory 123,maxmem=456 --memory 555 will be equivalent to --memory 
>> 555,maxmem=456. Is that fine for you needs?
>>
>> I think it's a bit nicer and has benefits if you want to pass in an 
>> extra option to a virt-install script or similar
>>
> 
> Thanks Cole,
> 
> Yes, this does look better. However, IMO, the user should be warned if 
> they do something like '--memory 123,maxmem=456 --memory 555' because 
> it's not clear if they want '123' or '555'.
> 
> I was thinking of defining and using a custom argpase action to warn the 
> user - see attached patch (incomplete - likely missing many single-use 
> args).
> 
> What do you think of this approach?
> 

I dunno... are there any other command line tools that warn in this 
case? I can't think of any offhand. The warning may save users a bit of 
time if they accidentally specify an option twice and get unexpected 
results, but it will also be noise for other users.

For example, I know it's a common pattern for people to treat 
virt-install effectively as 'write once' and stuff a working invocation 
in script. So say a user has a simple script like

#!/bin/bash
virt-install --name test --memory 2048 --disk size=10 --cpu host-model "$@"

They invoke it like 'myscript --location $URL' or similar. But later on, 
or for some invocations, they want to specify more memory (myscript 
--memory 4096...) or a different cpu config (myscript --cpu 
host-passthrough). Now they see a warning even though it's entirely 
intended. So it's not a total win either way IMO,

Can you describe the case where this bit you? Maybe it will help me 
understand better

Thanks,
Cole