Fixed setting unlimited maximum partition size

[lslezak]

Problem

• Partitioner: Wrong evaluation of "undefined" Maximum size of a disk (swap) #1065
• The maximum partition size cannot be set to "unlimited", using empty value results in the default maximum size

Example: Changing the default 2GB max size is not possible, it is always restored back:

Details

• The problem is that the "unlimited" value is represented using the undefined value in the web UI.
• But undefined cannot be sent over D-Bus because D-Bus does not have concept for undefined, nil or NULL values, Iin that case the MaxSize is simply missing the sent D-Bus data.
• When the D-Bus service creates a Volume object it first initializes it with the default data from the YAML product configuration file. Then it updates the attributes using the D-Bus data. Obviously when a value is missing in the D-Bus then it keeps the default value from the config. And that's the problem.

Solution

• Set the "unlimited" value when the MaxSize attribute is missing in the D-Bus data.

Questions

• The fix has a drawback, the current code allows sending only partial data set and ensures the defaults from the config file are used for missing values.
• This won't work any more for the maximum size as a missing value won't be considered as a "use the default" but as "use the unlimited size".
• Can this have some bad consequences?
• The code works, but is it safe in all scenarios?

Alternative Solution

• If this fix is not correct then we should probably introduce a new key in the D-Bus data, something like MaxSizeUnlimited with true / false values which can be transferred via D-Bus...

Testing

• Tested manually

Now it is possible to unset the maximum size:

[joseivanlopez]

IMHO, we can assume unlimited max size if the value does not come from D-Bus, so I think the fix is ok.

[coveralls]

coverage: 74.671% (+0.002%) from 74.669%
when pulling 90c13f2 on max_size_fix
into 05ea8cd on master.

[joseivanlopez]

LGTM