Mailinglist Archive: yast-devel (211 mails)

< Previous Next >
Re: [yast-devel] Some notes about new storage API
On Tue, Oct 13, 2015 at 01:05:16PM +0200, Josef Reidinger wrote:
On Tue, 13 Oct 2015 11:29:44 +0200
Arvin Schnell <aschnell@xxxxxxxx> wrote:

On Tue, Oct 13, 2015 at 10:14:03AM +0200, Josef Reidinger wrote:

I'll do more experiments with this as soon as the prototype is
easily installable. But looks pretty clear that it would be
fairly easy to fix the un-rubism by adding the corresponding
methods in the Ruby side in case we decide we are so purist that
we cannot live with the current API. :-) So nothing to fix in the
libstorage (C++) side.

I agree, that it make sense to have some helpers to have ruby
bindings more "ruby".

Just remember that those need documentation and test cases.

a) Is device_graph always an object representing the whole
graph?

The devicegraph always represents the whole graph.


Well, in general I do not like this API before and I also do not
like it now :)
It is not object oriented and whats more device_graph is god like
object.

Please elaborate this. What do you mean by God like object? A
object that holds all storage objects?

Yes, if you have object that hold everything it is not graph, but flat
structure.

Sure it's a graph, see
https://en.wikipedia.org/wiki/Graph_%28mathematics%29, esp. "a
graph is a [...] pair G = (V, E) comprising a set V of
vertices [...] together with a set E of edges [...]".

Regarding god objest see
https://en.wikipedia.org/wiki/God_object it is one extrem, where you
have too powerfull object.

I consider a single search function, as was proposed, as too
powerful (among other problems already explained).

Please explain that, esp. what problems you see with the existing
target map and how you still see this problems with the new
design.

Problem of target map is that it is not much flexible. It is not
object, it is more like data. And if data changed, then all methods
that use it need to adapt. In general rule for design is

1) if data is fixed and just way how it is interpreted changed, then
create data object and have methods that work on top of it.

2) if data is changed, but way how it is worked with them do not
change, then use object that represent such data.

Reason is easy changes. If you need to add new data type, is it easier
to change device_graph and all methods that do finding or use some kind
of child to represent it and connect it to rest of system?

These general rules don't help much when we discuss concrete
examples.


I prefer to have graph of objects that points to each other

The device-graph is just that and the functions to query the
"pointers" exist.

That is something different. Now you have one object that holds it. so
it is like

device_graph -> A, B, C, D, E

That is not a graph but just a list of nodes without edges.

if it use graph of object then it can look like

device_graph -> filesystems -> A, B
-> physical_devices -> C, D
-> containers -> E
and what is more important E point to C, D....C can point to partition
C1, C2 and C1 can point to A and C2 can point to B.

In a graph everything can point to everything. The "pointer" can
even hold data.

This way if something need disk, it can query it for partitions and
inspect its filesystems without knowing if it is teoretic device graph,
real one or modified one.

In the current prototype the functions can work on all graphs,
whether it's the "system", the "staging" or "my ideas" graph.

and it is easy to say what object it returns. It also allows
easy introspection and better documentation that allows easier
usability.

In general your remarks are to buzz-work like to comment on them.

OK, let me explain it better. and use ruby as example.

If I am interested what e.g. device_graph provide me, I can do
device_graph.methods which in case passing device_graph everywhere do
not should interesting stuff. Also methods is not documented in it and
lives elsewhere.

Sorry, I don't understand that.

In case when you use object like approach then you can do something like

disk.methods -> partitions, label, ...

and then you can check what provide you partitions, what provide you
label, etc.

If I get you right you want to replace documentation by
introspecion.

So it is easier to understand whole picture as it is layer knowledge.
You have reasonable small Disk object and if it return in some method
e.f. Partition object, then again you can check it and see what it
provides if you need it.

The documentation will include a tree of storage classes so you
can get that information very easy.

Counter example now is Storage module in yast2-storage which is
overloaded by methods. Current approach in new libstorage for me looks
like we have all methods for device_graph which is just enclosed in
namespaces like
Storage::Filesystem.find_by_mountpoint(device_graph, "/")

which for me is just something like
device_graph.find_filesystem_by_mountpoint("/")

Then you don't understand the basic prinicipe of OOP, that the
methods are part of the class that hold the data.

In general agreed, but if you have a get_xx and a set_xx function
a find_by_xx seems natural.

That depends how often it will be extended.

It should not happen so often. And you will have to add the
getter and setter anyway.

ciao Arvin

--
Arvin Schnell, <aschnell@xxxxxxxx>
Senior Software Engineer, Research & Development
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284
(AG Nürnberg)
Maxfeldstraße 5
90409 Nürnberg
Germany
--
To unsubscribe, e-mail: yast-devel+unsubscribe@xxxxxxxxxxxx
To contact the owner, e-mail: yast-devel+owner@xxxxxxxxxxxx

< Previous Next >
Follow Ups