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

[Olivier MATZ]

Hi,

On Wed, Nov 15, 2017 at 04:12:07AM +0000, Wiles, Keith wrote:
> 
> 
> > 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.

On my side, I think this patch goes in the correct direction:
- it solves an issue of the command line library
- it replaces a specific dpdk code by a well-known library which is widely used

Olivier