Re: [dpdk-dev] [PATCH] Add external parser support for unknown commands.

[Neil Horman <nhorman@tuxdriver.com>]

On Mon, Nov 03, 2014 at 03:26:50PM -0800, Stephen Hemminger wrote:
> On Mon, 3 Nov 2014 16:50:15 +0000
> "Wiles, Roger Keith" <keith.wiles@windriver.com> wrote:
> 
> > 
> > > On Nov 3, 2014, at 10:06 AM, Neil Horman <nhorman@tuxdriver.com> wrote:
> > > 
> > > On Mon, Nov 03, 2014 at 02:25:51PM +0000, Wiles, Roger Keith wrote:
> > >> 
> > >>> On Nov 3, 2014, at 8:16 AM, Bruce Richardson <bruce.richardson@intel.com> wrote:
> > >>> 
> > >>> On Mon, Nov 03, 2014 at 02:08:46PM +0000, Wiles, Roger Keith wrote:
> > >>>> 
> > >>>>> On Nov 3, 2014, at 4:41 AM, Bruce Richardson <bruce.richardson@intel.com> wrote:
> > >>>>> 
> > >>>>> On Sun, Nov 02, 2014 at 04:28:28PM -0600, Keith Wiles wrote:
> > >>>>>> Allow for a external parser to handle the command line if the
> > >>>>>> command is not found and the developer has called the routine
> > >>>>>> int cmdline_set_external_parser(struct cmdline * cl,
> > >>>>>>                              cmdline_external_parser_t parser);
> > >>>>>> function to set the function pointer.
> > >>>>>> 
> > >>>>>> The function for the external parser function should return CMDLINE_PARSE_NOMATCH
> > >>>>>> if not able to match the command requested or zero is handled.
> > >>>>>> 
> > >>>>>> Prototype of external routine:
> > >>>>>> int (*cmdline_external_parser_t)(struct cmdline * cl, const char * buy);
> > >>>>>> 
> > >>>>>> Signed-off-by: Keith Wiles <keith.wiles@windriver.com>
> > >>>>> 
> > >>>>> Hi Keith,
> > >>>>> 
> > >>>>> what is the expected use case for this? Is it for embedding other programming languages alongside the existing DPDK command-line or some other purpose? [Perhaps the use case could be called out in the patch description]
> > >>>> 
> > >>>> Hi Bruce,
> > >>>> 
> > >>>> I guess the external parser could be used for other programming languages, but the case I was looking at was to provide a default escape from the command line parser to allow my application to handle the commands not understood by the parser. Now that you point it out I could use something like ‘%<line-of-script-code>’ to execute a single line of script code, which is a good idea (thanks).
> > >>>> 
> > >>>> One case I am looking at is when you want to execute a command and do not want to add the support into the commands.c file for every possible command. Take the case where you have a bunch of scripts (Lua) in a directory much like a bin directory. Then you could type foo.lua or foo on the command line and execute the foo.lua having the application detect you want to load and run a Lua script after it has finished parsing for the builtin commands.
> > >>>> 
> > >>>> For Pktgen I had to add a command called ‘run <filename> <args…>’ to support running a script with arguments. I also needed to add a argvlist type to cmdline to not error out on that command and split up the args into a argv list like format. (Maybe I need to submit that code??) It seemed more straight forward to just pass the command line to the application to run the command. I understand that seems like a minor point, but it does make it easier to use and to support the features I want to support in my PoC.
> > >>>> 
> > >>>> Using this method you can just type the name instead of something like ‘run foo.lua’ or just ‘run foo’ and let the code figure out what to run. I have more plans for this features as well and have not finished the basic PoC yet. If you want a peek I can show you what I am working on currently.
> > >>>> 
> > >>>> Does this help and do I really need to add all of this to the commit message :-)
> > >>>> 
> > >>> Thanks for the explanation. However, if you are looking to have the application handle a bunch of commands itself, why does it need to use the commandline library at all? Why not just have the app handle all the commands instead of some of them?
> > >> 
> > >> I guess that would be reasonable, but then I would have to add support for all of the command line parsing being done in the cmdline code. Think of this as a default case for the parser and to me that makes more sense then just doing my own command line design. In the cmdline code you guys provided is a lot of features like history, control key support, arg parsing (IP, MAC) and many others. I would rather not have to write that code myself.
> > >> 
> > >> The default case is the same behavior today, with giving a no match error unless they add the external parser.
> > > 
> > > It seems alot simpler than that to me.  Looking at the test applications, the
> > > command line parser expects the application to create an array of
> > > cmdline_parse_ctx_t structures to support new option parsing.  If your goal is
> > > to support other languages, it seems to make more sense to just use foreign
> > > language bindings to merge your coding language support with the DPDK
> > > (ostensibly you will already have to do that if you want to use other parts of
> > > the DPDK).
> > Hi Neil,
> > 
> > A true language binding like Lua or one of those other languages :-) you are correct to believe binding directly using ‘C’ code is the right solution . In Pktgen I use Lua as the direct language binding and extend Lua with specific Pktgen functions.
> > 
> > What I am doing here is to add a default case to cmdline code, which just happens to allow me to parse the cmdline in the application. Being able to execute say a line of script code is not really the requirement IMO. Being able to extend the cmdline code with a default case is a good feature and allows the developer to extend cmdline for some simple cases. The cmdline code is kind of simple, but does require a fair amount of structures, code and understanding to write a complex extendable command line interface. It does seem hard to find a clean, simple and usable embedded command line code base is not very easy to locate. 
> > 
> > Adding a true language binding really requires using code to extend the language as I did with Lua and Pktgen. It could have been done with any language I just picked Lua, but the patch does not really add support for a language other then giving some support for someone to handle the no_match case.
> > 
> > The use case for this feature is not just for Pktgen, but another solution I hope everyone will find useful when I get it more complete.
> > 
> > Thanks
> > ++Keith
> > 
> > PS. on a different topic I was thinking about suggesting and writing a patch to add Lua with DPDK specific binding and extensions. (also allowing those `other` languages too :-) Being able to use a scripting language and be able to call DPDK API’s could be useful. How useful not sure at this time. (If you want to talk about this topic please start a new thread).
> > > 
> > > Am I missing something?
> > > Neil
> > > 
> > > 
> > >>> 
> > >>> /Bruce
> > >> 
> > >> Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533
> > 
> > Keith Wiles, Principal Technologist with CTO office, Wind River mobile 972-213-5533
> 
> I wouldn't invest a lot of sweat in the command line parser.
> The one in the DPDK is "good enough" for what it needs to do, but really isn't
> very complete and flexible. Seems like the kind of thing that doesn't really even
> need to be in DPDK. Better off being part of some other library.
> 
Well, something needs to be there to parse the libraries' common options, though
I agree, making eal_cmdline just a registration frontend to getopt or
getopt_long would be sufficient.

Neil