Re: [RFC] Yet another option for DPDK options

[Arnon Warshavsky <arnon@qwilt.com>]

On Fri, Jun 3, 2016 at 2:50 PM, Neil Horman <nhorman@tuxdriver.com> wrote:

> 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
>
>
If the there is no configuration structure , rather an opaque configuration
key/value store ,
the user applications can set and get knobs that are not seen by anyone
(library) that does not know them by name

e.g

int num_nodes = getCfgInt ( cfgObject , "eal" , "num_numa_nodes");
int delay = getCfgInt ( cfgObject , "drivers.ixgbe" , "some_delay");
setCfgInt (cfgObject , "my_app" , "num_days" , 7);
setCfgString (cfgObject , "my_app" , "best_day" , "Wednesday");

/Arnon