> -----Original Message----- > From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Neil Horman > Sent: Thursday, June 4, 2015 2:56 PM > To: Wiles, Keith > Cc: dev at dpdk.org > Subject: Re: [dpdk-dev] [RFC PATCH] eal:Add new API for parsing args at > rte_eal_init time > > On Thu, Jun 04, 2015 at 11:50:33AM +0000, Wiles, Keith wrote: > > Hi Stephen > > > > On 6/3/15, 7:12 PM, "Stephen Hemminger" <stephen at networkplumber.org> > wrote: > > > > >On Wed, 3 Jun 2015 13:49:53 -0500 > > >Keith Wiles <keith.wiles at intel.com> wrote: > > > > > >> +/* Launch threads, called at application init() and parse app > > >> +args. */ int rte_eal_init_parse(int argc, char **argv, > > >> + int (*parse)(int, char **)) > > >> +{ > > >> + int ret; > > >> + > > >> + ret = rte_eal_init(argc, argv); > > >> + if ((ret >= 0) && (parse != NULL)) { > > >> + argc -= ret; > > >> + argv += ret; > > > > > >This won't work C is call by value. > > > > I tested this routine with Pktgen (again), which has a number of > > application options and it appears to work correctly. Can you explain > > why this will not work? > > > > Regards, > > ++Keith > > > > > > > > > Stephen was thinking that your intent was to have argc, and argv modified at > the call site of this function (i.e. if you called rte_eal_init_parse from > main(), > then after the call to rte_ela_init_parse, argc would be reduced by ret and > argv > would point forward in memory ret bytes in the main function, but they wont. > It doesn't matter though, because you return ret, so the caller can do that > movement themselves. As you note, it works. > > Note that if it was your intention to have argc and argv modified at the call > site, > then Stephen is right and this is broken, you need to modify the prototype to > be: > int rte_eal_init_parse(int *argc, char ***argv) > > and do a dereference when modifying the parameters so the change is seen at > the call site. > > That said, I'm not sure theres much value in adding this to the API. For > one, it > implies that dpdk arguments need to come first on the command line. While > all the example applications do that, theres no requirement that they do so, > and this function silently implies that they have to, so any existing > applications > in the wild that violate that assumption are enjoined from using this > > It also doesn't really save any code. If we pick an example app (I'll us > l2fwd- > jobstats), We currently have this: > > /* init EAL */ > ret = rte_eal_init(argc, argv); > if (ret < 0) > rte_exit(EXIT_FAILURE, "Invalid EAL arguments\n"); > argc -= ret; > argv += ret; > > /* parse application arguments (after the EAL ones) */ > ret = l2fwd_parse_args(argc, argv); > if (ret < 0) > rte_exit(EXIT_FAILURE, "Invalid L2FWD arguments\n"); > > With your new API we would get this: > > ret = rte_eal_init_parse(argc, argv, l2fwd_parse_args) > if (ret < 0) > rte_exit(EXIT_FAILURE, "Invalid arguments - not sure what\n"); > > Its definately 5 fewer lines of source, but it doesn't save any execution > instructions, and for the effort of that, you loose the ability to determine > if it > was a DPDK argument or an application argument that failed. > > Its not a bad addition, I'm just not sure its worth having to take on the > additional API surface to include. I'd be more supportive if you could > enhance > the function to allow the previously mentioned before/after flexibiilty. > Then we > could just deprecate rte_eal_init as an API call entirely, and use this > instead.
Before/after would be very useful, a lot of applications use only "-c" and "-n" EAL command line parameters and "-c" in many cases is redundant as application can calculate core mask from its own parameters, and "-n" just a required parameter which can be defaulted to a platform specific value. So in addition to rte_set_application_usage_hook() it would be nice to have some more general way of overwriting eal initialization parameters. > > Neil
