[dpdk-dev] [RFC] Yet another option for DPDK options

[Matthew Hall]

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