Re: [RFC] Yet another option for DPDK options

[Neil Horman <nhorman@tuxdriver.com>]

On Fri, Jun 03, 2016 at 12:01:30PM +0100, Bruce Richardson wrote:
> On Fri, Jun 03, 2016 at 11:29:43AM +0100, Bruce Richardson wrote:
> > 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);
> > 
> From chatting to a couple of other DPDK dev's here I suspect I may not have
> been entirely clear here with this example. What is being shown above is building
> up a "config-file" in memory - or rather a config structure which happens to
> have the idea of sections and values as an ini file has. There is no actual
> file ever being written to disk, and for those using any non-ini config file
> structure for their app, the code overhead of using the APIs above should be 
> pretty much the same as building up any other set of key-value pairs in
> memory to pass to an init function.
> 
> Hope this is a little clearer now.
> 
I'm fine with the idea of reusing the config file library that currently exists,
or more to the point, modifying it to be usable as a configuration API, rather
than a configuration file parser.  My primary interest is in separating the user
configuration mechanism from the internal library configuration lookup
mechanism.  What I would really like to be able to see is application developers
have the flexibiilty to choose their own configuration method and format, and
programatically build a configuration for the dpdk on a per-instance basis prior
to calling rte_eal_init

It seems like this approach satisfies that requirement
Neil

> /Bruce
>