[dpdk-dev] [RFC] cmdline: rework as a wrapper to libedit

[Wiles, Keith]

> On Nov 9, 2017, at 5:43 AM, Adrien Mazarguil <adrien.mazarguil at 6wind.com> wrote:
> 
> This patch removes all code associated with symbols not internally relied
> on by other DPDK components, makes struct cmdline opaque and then proceeds
> to re-implement the remaining functionality as a wrapper to the editline
> library (also known as libedit) [1].
> 
> Besides adding a new external dependency to its users, its large impact on
> librte_cmdline's API/ABI also warrants a major version number bump.
> 
> While librte_cmdline served DPDK well all these years as a small, easy to
> use and self-sufficient interactive command-line handler, it started to
> show its limits with testpmd's flow (rte_flow) command, which required
> support for dynamic tokens and very long commands.
> 
> This is the main motivation behind this rework. Long commands often need to
> be displayed on multiple lines, which are not properly supported by
> librte_cmdline's limited terminal handling capabilities, resulting in a
> rather frustrating user experience.
> 
> Testpmd being one of the main tools used by PMD developers and given flow
> command lines won't get any shorter, this issue had to be addressed.
> 
> Three options were considered:
> 
> - Fixing and enhancing librte_cmdline.
> 
>  The amount of work necessary to add support for edition on multiple lines
>  was deemed significant and the result would still have lacked in some
>  areas, such as working backspace/delete keys in all terminals (i.e. full
>  termcap support).
> 
> - Making testpmd directly rely on a more capable library.
> 
>  All testpmd commands rely on the cmdline_parse interface provided by
>  librte_cmdline. This approach would have required either a complete
>  rewrite or importing the missing bits from librte_cmdline to wrap them
>  around the new library, which naturally led to...
> 
> - Converting librte_cmdline as a wrapper to a more capable library.
> 
>  Let's be honest, interactive command line handling isn't what makes DPDK
>  shine. It's also far removed from its core functionality, but is still
>  necessary in order to easily implement test and example programs; the
>  cmdline_parse interface is particularly good at this.
> 
>  DPDK actually only relies on cmdline_parse. By removing all the other
>  unused interfaces, implementing what remains on top of a different
>  terminal-handling library would be quick and easy.
> 
> This last approach was chosen for the stated reasons. Libedit is
> well-known, BSD-licensed, widely available [2], used by many projects, does
> everything needed and more [3].
> 
> This rework results in the following changes:
> 
> - Removed circular buffer management interface for command history
>  (cmdline_cirbuf.c), command history being handled by libedit.
> - Removed raw command-line interpreter (cmdline_rdline.c).
> - Removed raw terminal handler (cmdline_vt100.c).
> - Removed all test/example code for the above.
> - Re-implemented high level interactive and non-interactive command-line
>  handlers (cmdline.c and cmdline_socket.c) on top of libedit using its
>  native interface, not its readline compatibility layer.
> - Made struct cmdline opaque so that applications relying on librte_cmdline
>  do not need to include any libedit headers.
> - The only visible change for most applications besides being linked to
>  libedit is they do not have to include cmdline_rdline.h anymore.
> 
> As an added bonus, terminal resizing is now automatically handled.
> 
> In the future, cmdline_parse could use libedit's advanced tokenizer as
> well to interpret quoted strings and escape sequences.
> 

I do agree that cmdline is getting pretty old and using libedit is one solution around the long commands, but it has a lot more problems IMO.

I do not agree it has severed DPDK well, just look at test-pmd and the hoops people have to jump thru to get a new command or variation of an existing command integrated into test-pmd it is very difficult. Also if you look at the command sets in test-pmd they are very odd in that similar commands can some times be set up completely different as cmdline is too rigid and difficult to use.

I had decided to not use the circular buffer code in cmdline as it did have a few problems for what I wanted and decided to write a standard gap buffer scheme used in most editors for lines. I had looked at libedit at one point decided I did not want another dependence for DPDK. I expect even my version does not solve the long line problem, but we can convert to libedit. (and toss my pretty code :-)

Fixing the long line problem is a very minor issue compared to everything else wrong with cmdline. I would suggest we look at CLI and improve it instead. We can add libedit to CLI and then finish testing the CLI with test-pmd. The first time I converted test-pmd I did remove and simplify the commands, but I was afraid that would cause a lot of problems for testing and scripts that people have written, but it is possible to fix these problems too.


I do not think fixing cmdline is the best answer and working to convert over to CLI is the better answer here.


Regards,
Keith