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

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

On Thu, Jun 02, 2016 at 04:08:37PM -0400, Neil Horman wrote:
> On Thu, Jun 02, 2016 at 07:41:10PM +0000, Wiles, Keith wrote:
> > 
> > On 6/2/16, 12:11 PM, "Neil Horman" <nhorman@tuxdriver.com> wrote:
> > 
> > >
> > >1) The definition of a config structure that can be passed to rte_eal_init,
> > >defining the configuration for that running process
> > 
> > Having a configuration structure means we have to have an ABI change to that structure anytime we add or remove an option. I was thinking a very simple DB of some kind would be better. Have the code query the DB to obtain the needed information. The APIs used to query and set the DB needs to be very easy to use as well.
> 
> Thats a fair point.  A decent starting point is likely a simple struct that
> looks like this:
> 
> struct key_vals {
> 	char *key;
> 	union {
> 		ulong longval;
> 		void *ptrval;
> 	} value;
> };
> 
> struct config {
> 	size_t count;
> 	struct key_vals kvp[0];
> };
> 
> > 
> > Maybe each option can define its own structure if needed or just a simple variable type can be used for the basic types (int, string, bool, …)
> > 
> Well, if you have config sections that require mulitiple elements, I'd handle
> that with naming, i.e. if you have a config group that has an int and char
> value, I'd name them "group.intval", and "group.charval", so they are
> independently searchable, but linked from a nomenclature standpoint.
> 
> > Would this work better in the long run, does a fixed structure still make sense?
> > 
> No. I think you're ABI concerns are valid, but the above is likely a good
> starting point to address them.
> 
> Best
> Neil

I'll throw out one implementation idea here that I looked at previously, for
the reason that it was simple enough implement with existing code.

We already have the cfgfile library which works with name/value pairs read from
ini files on disk. However, it would be easy enough to add couple of APIs to
that to allow the user to "set" values inside an ini structure as well. With
that done we can then just add a new eal_init api which takes a single
"struct rte_cfgfile *" as parameter. For those apps that want to just use
inifiles for configuration straight, they can then do:

cfg = rte_cfgfile_load("my_cfg_file");
rte_eal_newinit(cfg);

Those who want a different config can instead do:

cfg = rte_cfgfile_new();
rte_cfgfile_add_section(cfg, "dpdk");
foreach_eal_setting_wanted:
	rte_cfgfile_set(cfg, "dpdk", mysetting, myvalue);
rte_eal_newinit(cfg);

We can standardize on a sectionname, or a couple of standard section names that
are used by DPDK, so that the rest of the config file can contain other data
for the app itself.

What do people think. I mainly like it because it gives us good reuse of what
is already there, and enhances our existing library. As well as this it makes
it trivially easy for apps to use ini files - which seem to be very popular here
- while still giving flexibility for others to use whatever other config format
their app prefers.

/Bruce