[ovirt-devel] improving VDSM error reporting

[Yoav Kleinberger]

Hi all,

This idea was born from this bug: https://bugzilla.redhat.com/730619 

If, for example, creating a new storage domain 
fails because there's no space left, the user gets:

            "Error creating a storage domain"

which is not very helpful, since the real problem (no space) is not reported.

            "Error creating a storage domain"

            [i] No space left on device

Where [i] is some widget the user can open to see details, 
or other element the UX team find acceptable.

Nir Soffer and I believe a good solution is the following:

1. Currently VDSM sends a dictionary  {'status': {'code': code, 'message': msg}}. 
   The code is some number that Engine recognizes and has a localized
   message for. The msg parameter is ignored by Engine, and contains
   a default, not informative, string like "Error creating a storage domain"

2. We suggest adding a new key to this dictionary, call it "details", 
   which will contain the string representation of the actual exception thrown
   in Python (in this case, OSError with the string "[Errno 28] No space left
   on device"

3. The Engine will look for this key, and display the string inside a "details" 
   section which will be added to the current dialog box. The user gets the
   usual error indication, but has a small "details" icon, which he can click
   to see more information.

The advantages are:
1. Simple to implement
2. Will improve the situation for any error thrown from Python 
   - the user will get a clearer message.
3. New VDSM with old Engine is not a problem, the engine will not 
   look for this key at all
4. New Engine with old VDSM is also easy to handle: the engine will not 
   display "details" if this key is absent.

Disadvatage is that the "details" will be non-localized, but this is 
natural for technical details. 

Why not use the existing "msg" field? because a new engine with an old VDSM
will display uninformative, duplicate messages for all errors (the current msg
field is simply a duplicate of the engine error name).

What do you think?

Yoav K