Re: [PATCH i2c-tools v3 2/2] i2ctransfer: Add optional message modifier flags

[Wolfram Sang <wsa+renesas@sang-engineering.com>]

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Hi Benoît,

On Tue, Jan 27, 2026 at 10:25:58AM +0100, Benoît Monin wrote:
> Allow setting protocol mangling and repeated start elision flags of an i2c
> message with a set of optional command-line flags. These optional flags
> are parsed at the beginning of the DESC field up to a read or write flag.
> 
> For example, to read one byte from address 0x50 followed by a stop, then
> write two bytes at 0x54 on bus 0, one would call i2ctransfer as follow:
> 
>     i2ctransfer 0 pr1@0x50 w2@0x54 0x10 0x20
> 
> Since the new flags are optional, this patch preserves the compatibility
> of the i2ctransfer syntax.
> 
> Handling of the message flags is done in add_flag_if_supported(). This
> function checks if the flag is defined at compile time and if the adapter
> supports the required functionality to handle the flag.
> 
> Signed-off-by: Benoît Monin <benoit.monin@bootlin.com>

I don't have a controller supporting 'mangling' here at the moment, but
the code looks good and my regression tests went fine. There is one
thing about error handling, though:

> +			for (ret = 0; *arg_ptr && !ret; arg_ptr++) {
> +				ret = add_flag_if_supported(&flags, funcs, *arg_ptr);
> +				if (ret < 0)
> +					goto err_out_with_arg;
> +			}
> +			if (ret != 1) {
> +				fprintf(stderr, "Error: Missing direction flag 'r' or 'w'\n");
>  				goto err_out_with_arg;
>  			}

This error message now only shows up if the 'rw'-flag is missing at the
end of the commandline:

# ./i2ctransfer -y 0 p
Error: Missing direction flag 'r' or 'w'
Error: faulty argument is 'p'

Otherwise it complains about '@' not being a flag:

# ./i2ctransfer -y 0 p@0x1a
Error: Unsupported flag '@'
Error: faulty argument is 'p@0x1a'

It would be nice if '@' would be recognized as a terminator for the
flags and would then complain about the missing direction flag, or?

Happy hacking,

   Wolfram


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