Re: [RFC] Yet another option for DPDK options

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Jun 03, 2016 at 10:57:22AM +0100, Bruce Richardson wrote:
> On Thu, Jun 02, 2016 at 07:17:05PM -0700, Matthew Hall wrote:
> > On Thu, Jun 02, 2016 at 06:34:58PM -0400, Neil Horman wrote:
> > > > This sort of code is very 1970s / ioctl / messy binary. And doesn't buy any 
> > > > performance advantage because it's just for config.
> > > > 
> > > What!?  I can't even parse that sentence.
> > 
> > I would not want to have to use the structure you proposed in user-readable 
> > code. It looked a lot like ugly ioctl stuff and I found the sysctl style 
> > interface easier to read. I don't see why that would be hard for anyone to 
> > parse but nevertheless.
> > 
> > > > https://www.freebsd.org/cgi/man.cgi?sysctl(3)
> > > > 
> > > I can't even begin to understand what you're after here.  sysctl provides a
> > > heirarchy in _exactly_ the same way that I just proposed, by texual consistency
> > > in naming.
> > 
> > I didn't object to the hierarchy part, but the user hostility of the example 
> > proposed.
> > 
> > > > http://json-c.github.io/json-c/json-c-0.12/doc/html/json__object_8h.html
> > > > 
> > > So, this is a fine interface to convert text config to a code format, but thats
> > > a decision that application should be making, not something dpdk should mandate
> > 
> > You're thinking way too narrowly here for what I am working to convey. I 
> > wasn't meaning to say JSON had to be used. I was saying, the kind of 
> > lightweight object-based API they used for modeling JSON has worked very well 
> > for modeling config data inside of my app. IE, simple functions for working 
> > with the following sort of entities (which are used in many file / interchange 
> > systems like JSON, MsgPack, YAML, etc.):
> > 
> > Objects:
> > * hashes, arbitrarily nested
> > * arrays, arbitrarily nested
> > 
> > Atoms:
> > * strings - textual
> > * strings - binary (something we should add for DPDK)
> > * integers
> > * floats / doubles
> > * booleans
> > 
> > In general I am seeing two good approaches for nesting:
> > 
> > 1. name nesting like MIB variable "x.y.z.a.b.c" - this is how sysctl works
> > 2. object nesting- this is how JSON, YAML, MsgPack, INI (implicitly w/ section 
> > names), XML etc. work...
> > 
> > to express this in the Python / Ruby / JS style syntax it would be:
> > 
> > config['x']['y']['z']['a']['b']['c']
> > using json-c it would be like
> > 
> > json_object_object_get()... until a json_object_TYPE_get().
> > 
> > What I've done for these in the past, is to make something that can parse the 
> > sysctl-style name x.y.z.0.a.b.c, detect if each dotted-item is a string, in 
> > which case reach inside the dict for the string or return NULL if not found, 
> > and if it's a number reach inside the array for that index and return NULL if 
> > not found. Here is a Python example how to take the sysctl style and look it 
> > up inside some objects. The same thing could be done using anything with at 
> > least as rich of features as what json-c provides...
> > 
> > RE_IS_INT = re.compile('^[0-9]+$')
> > def retrieve_path(data, path):
> >     if isinstance(path, basestring):
> >         path = path.split('.')
> > 
> >     if isinstance(data, Mapping):
> >         result = data.get(path[0])
> >     else:
> >         if not RE_IS_INT.match(str(path[0])):
> >             return None
> >         i = int(path[0])
> >         result = data[i] if len(data) > i else None
> > 
> >     if len(path) == 1:
> >         return result
> >     else:
> >         if result:
> >             return fetch(result, path[1:])
> >         else:
> >             return None
> > 
> > > Neil
> > 
> > Matthew
> 
> I'm afraid I don't see the need to expand out to such a large range of types, or
> to add object-type nesting. I'm a big fan of simplicity, and I think Neils
> original suggestion of basic name-value pairs is a good one to start with. The
> dot notation should work fine for any hierarchies we want to have. If we get
> beyond having 2 levels in a hierarchy of config, I think we may have gone
> overboard in making things too fine-grained configurable!
> 
Minor correction: re-reading my mail afterwards, I realise I actually meant 
2 dots in the name, ie. 2 sublevels, or 3 levels, rather than 2 levels! Must
proofread more.

However, I expect most folks still got my point despite the typo! :-)

/Bruce