Re: [24.03 RFC 0/3] Add argument manipulation library

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu,  2 Nov 2023 17:28:46 +0000
Bruce Richardson <bruce.richardson@intel.com> wrote:

> DPDK has traditionally assumed that apps are written where argc/argv
> parameters are passed directly to rte_eal_init() and then app arguments
> are handled afterwards, as is done in the DPDK apps and examples.
> 
> However, based on other projects, like VPP and OVS, we know that this is
> often not the case. Instead, the apps build up argument lists internally
> themselves and pass those to the init function, and DPDK never directly
> accesses the real argc/argv values.
> 
> Therefore, let's make this mode of operation a little easier to use, by
> adding in an args library to allow an app to dynamically build up an
> args array and then pass that to EAL init. This library allows things
> like, for example, initializing a list from argv and then checking if a
> particular parameter is present, adding it if not. All the basics of
> such a library are included in patch 1, and I've found it of use myself
> when writing some simple apps internally using DPDK.
> 
> Patches 2 and 3 go a little further than this, and allow for a slightly
> different use-case, that where an app may want to allow mixing of EAL
> arguments in with app args. These patches allow the user to query if a
> particular argument is an EAL arg or not, or a valid app argument. The
> idea here would be, that an app could go through it's argument list,
> building up an argument list for EAL init by just picking out the EAL
> arguments from a full argument list. I'm less convinced of the value of
> this compared to the basics in patch 1, but I think the idea is
> interesting so seeking feedback on it.
> 
> Bruce Richardson (3):
>   args: new library to allow easier manipulation of cmdline args
>   eal: allow export of the cmdline argument parsing options
>   args: add functions to check parameter validity
> 
>  doc/api/doxy-api-index.md           |   1 +
>  doc/api/doxy-api.conf.in            |   1 +
>  lib/args/args.c                     | 301 ++++++++++++++++++++++++++++
>  lib/args/meson.build                |   5 +
>  lib/args/rte_args.h                 | 255 +++++++++++++++++++++++
>  lib/args/version.map                |  22 ++
>  lib/eal/common/eal_common_options.c |   9 +
>  lib/eal/include/rte_eal.h           |  14 ++
>  lib/eal/version.map                 |   1 +
>  lib/meson.build                     |   2 +
>  10 files changed, 611 insertions(+)
>  create mode 100644 lib/args/args.c
>  create mode 100644 lib/args/meson.build
>  create mode 100644 lib/args/rte_args.h
>  create mode 100644 lib/args/version.map
> 
> --
> 2.39.2
> 

It would be good to change rte_eal_init() from:
int rte_eal_init(int argc, char **argv);

to
int rte_eal_init(int argc, char * const *argv);

I.e it should not modify the argv's passed.
This would save unnecessary copy in applications that build synthetic args.
Example already exists in dumpcap.