Re: IIO trigger names are not actually unique

[Lars-Peter Clausen <lars@metafoo.de>]

On 05/05/2016 01:52 PM, Crestez Dan Leonard wrote:
> Hello,
> 
> I've been looking at trigger code and it seems to me that trigger->name
> is not guaranteed to be unique. This is despite the fact that it's
> documented as "@name: [DRIVER] unique name" on top of struct
> iio_trigger. Just like indio_dev->name it seems to be a mostly cosmetic
> label.
> 
> You can easily create a software trigger with a duplicate name if you
> enable CONFIG_IIO_HRTIMER_TRIGGER:
> 
> mkdir /sys/kernel/config/iio/triggers/hrtimer/`cat
> /sys/bus/iio/devices/trigger0/name`
> 
> It seems that trigger names are set at allocation time, mostly through
> some variant of:
> 
>     iio_trigger_alloc("%s-dev%d", indio_dev->name, indio_dev->id);
> 
> indio_dev->name is not guaranteed to be unique but indio_dev->id is. The
> are some exceptions, including st_sensors which does:
> 
>     iio_trigger_alloc("%s-trigger", indio_dev->name);
> 
> Since indio_dev->name is just the model name it seems that attaching two
> identical st_sensors devices will create two triggers with the same name.
> 

Yeah, this is certainly broken.

> The "current_trigger" for an iio_device is identified by name. If you
> have two triggers with the same name then the "first one" will be picked
> up, probably in registration order.
> 
> One solution would be to refuse to register triggers with duplicate
> names but that might cause probe errors in some cases.
> 

Well, it is broken anyway and wont work as expected, which means nobody
probably ever ran such a configuration, so we might return an error to
prevent unexpected behavior.

> Another option would be to just warn on duplicate names and provide a
> separate current_trigger_id which identifies the current trigger by
> numeric ID. In general it seems to me that it's better to identify
> entities by numbers rather than strings.

We could support writing triggerX to current_name as an alternative to the
name to get a unique identifier.