Re: [PATCH] cli: flush stdin before enabling cli

[Tom Rini <trini@konsulko.com>]

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On Tue, Mar 31, 2026 at 01:03:08PM +0200, Gregor Herburger wrote:
> Currently there is no possibility to flush stdin after autocommands are
> executed. If in the bootcmd the stdin is changed, e.g. from nulldev to
> serial, it could happen that junk characters sit in the fifo and appear
> on the cli.
> 
> Add a option to clear stdin before starting the CLI.
> 
> Signed-off-by: Gregor Herburger <gregor.herburger@linutronix.de>

Conceptually, good idea, thanks for doing it.

> 
> ---
> 
>  cmd/Kconfig  | 7 +++++++
>  common/cli.c | 6 ++++++
>  2 files changed, 13 insertions(+)
> 
> diff --git a/cmd/Kconfig b/cmd/Kconfig
> index 322ebe600c5..e08fbf27358 100644
> --- a/cmd/Kconfig
> +++ b/cmd/Kconfig
> @@ -47,6 +47,13 @@ config HUSH_SELECTABLE
>  	default y if HUSH_OLD_PARSER && HUSH_MODERN_PARSER
>  endmenu
>  
> +config CMDLINE_FLUSH_STDIN
> +	bool "Enable flushing input before starting cli"
> +	default n

We don't need default n as that's the default.

> +	help
> +	  When this option is enabled the stdin buffer will be flushed before
> +	  starting the CLI.
> +
>  config CMDLINE_EDITING
>  	bool "Enable command line editing"
>  	default y
> diff --git a/common/cli.c b/common/cli.c
> index 4694a35cd0e..42d27ed87e7 100644
> --- a/common/cli.c
> +++ b/common/cli.c
> @@ -295,6 +295,12 @@ err:
>  void cli_loop(void)
>  {
>  	bootstage_mark(BOOTSTAGE_ID_ENTER_CLI_LOOP);
> +
> +	if (IS_ENABLED(CONFIG_CMDLINE_FLUSH_STDIN)) {
> +		while (tstc())
> +			(void)getchar();
> +	}
> +
>  #if CONFIG_IS_ENABLED(HUSH_PARSER)
>  	if (gd->flags & GD_FLG_HUSH_MODERN_PARSER)
>  		parse_and_run_file();

This is flush_stdin() from common/autoboot.c, but that's a static
function. We should find a better spot for that perhaps and then call it
when required.

-- 
Tom

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