Re: [dpdk-dev] [PATCH 1/1] net/mlx4: add port parameter

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

Hey, thanks for reading.

On Fri, Mar 10, 2017 at 04:24:32PM +0000, Legacy, Allain wrote:
>> -----Original Message-----
>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Gaetan Rivet
>> Sent: Friday, March 03, 2017 10:40 AM
>...
>> +	errno = 0;
>> +	tmp = strtoul(val, NULL, 0);
>The robustness of the strtoul() could be improved with something like the following to catch non-integer characters following the port number.
>
>    char *end = NULL;
>    tmp = strtoull(val, &end, 0);
>    if ((val[0] == '\0') || (end == NULL) || (*end != '\0') || (errno != 0))
>
>

Thanks for the suggestion, I'd keep the strtoul though ;).
I will see into it for the v2, keeping in mind Stephen's remarks as 
well.

>> +	if (errno) {
>> +		WARN("%s: \"%s\" is not a valid integer", key, val);
>> +		return -errno;
>> +	}
>> +	if (strcmp(MLX4_PMD_PORT_KVARG, key) == 0) {
>> +		if (tmp >= MLX4_PMD_MAX_PHYS_PORTS) {
>> +			ERROR("invalid port index %lu (max: %u)",
>> +				tmp, MLX4_PMD_MAX_PHYS_PORTS - 1);
>> +			return -EINVAL;
>> +		}
>> +		conf->active_ports |= 1 << tmp;
>> +	} else {
>> +		WARN("%s: unknown parameter", key);
>> +		return -EINVAL;
>> +	}
>> +	return 0;
>> +}
>The usage of strtoul() should be moved to be within the strcmp(MLX4_PMD_PORT_KVARG, key) IF statement.  That way the "val" would only be parsed if "key" is "port" and it is expected that "val" is an integer.
>
>

This function was aimed at being generic.
If we consider that no other parameter would ever be added, then the 
strcmp should be scraped altogether, as this callback is only called 
upon parsing this parameter in the kvlist in the first place.

But we are in the control path, avoiding a useless strtoul at the price 
of making the function less useful seems an unnecessary tradeoff to me.

>> +	if (mlx4_args(pci_dev->device.devargs, &conf)) {
>> +		ERROR("failed to process device arguments");
>> +		goto error;
>> +	}
>It would be helpful for debugging if the error message included the devargs so that we can see what is wrong with the input.
>
>

Agreed.

>> +	/* Use all ports when none are defined */
>> +	if (conf.active_ports == 0) {
>> +		for (i = 0; i < MLX4_PMD_MAX_PHYS_PORTS; i++)
>> +			conf.active_ports |= 1 << i;
>> +	}
>
>Rather than use a loop to populate all active fields would a #define with an all ports mask be better suited to this.  Or alternatively just change the IF statement below to use the following and avoid the need for this loop altogether:
>
>if (conf.active_ports & !(conf.active_ports & (1 << i)))
>	continue;
>
>

I do not agree with removing this loop.

Your second solution will scatter the relevant bits concerning the 
default value of the active_port configuration option. While being 
slightly slicker it hides it unnecessarily from the reader.

The first solution might be interesting, however it makes this option 
dependent on two defines instead of one. If one had to change the 
default MAX_PHYS_PORT value for mlx4 (however unlikely it might be), 
then they would have to change the valid ALL_PORTS mask as well. In 
principle this contradicts DRY[1].

[1]: https://en.wikipedia.org/wiki/Don't_repeat_yourself

-- 
Gaëtan Rivet
6WIND