Re: [PATCH v4 1/2] i2c-tools: Allow passing device file paths

["Gero Schwäricke" <gero.schwaericke@sevenlab.de>]

Hi Wolfram,

On Sat Jul 11, 2026 at 9:24 PM CEST, Wolfram Sang wrote:
>> > -	i2cbus = lookup_i2c_bus(argv[optind]);
>> > -	if (i2cbus < 0) {
>> > -		help();
>> > -		exit(1);
>> > -	}
>> >  
>> >  	/* read address range if present */
>> >  	if (argc == optind + 3 && mode != MODE_FUNC) {
>> > @@ -321,7 +317,7 @@ int main(int argc, char *argv[])
>> >  		exit(1);
>> >  	}
>> >  
>> > -	file = open_i2c_dev(i2cbus, filename, sizeof(filename), 0);
>> > +	file = open_i2c_dev(argv[optind], &filename, sizeof(filename_buf), 0);
>> >  	if (file < 0) {
>> >  		exit(1);
>> >  	}
>> 
>> Removing this will change the error path, so a call that would
>> previously fail in lookup_i2c_bus() may now fail somewhere else,
>> changing error code and message. Same for all other tools.
>
> You mean that help() is not printed in some cases then? The error code
> is 1 in all cases, or am I missing something?

You're right, all error codes are converted to 1, so the error codes are
fine. Yes, I meant that a call with the current version may have failed
in the lookup_i2c_bus() call and printed for example

  Error: I2C bus name is not unique!

but with the new patch the lookup is done later, so it may fail in a
diffent location and print for example

  Error: No address specified!

instead. (Example for i2cdump)

This would be a problem, e.g., if someone wrote a script to check if
they have non-unique I2C bus names which uses i2cdump and evaluates
stderr for the string and if instead it returned the no address string
it assumed the check passed and all names are unique. Something like
this:

  i2cdetect -l | cut -f3 | sort -u | while read -r n; do
    i2cdump -y "$n" 2>&1 >/dev/null | grep -qF "Error: I2C bus name is not unique!" && echo "DUP: $n"
  done

That is the most reasonable example I found which may run into trouble
with the change.

Best,
Gero

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