Re: [RFC v2] iio: input-bridge: optionally bridge iio acceleometers to create a /dev/input interface

From: "H. Nikolaus Schaller" <hns@goldelico.com>
To: Bastien Nocera <hadess@hadess.net>
Cc: Jonathan Cameron <jic23@kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	Eric Piel <eric.piel@tremplin-utc.net>,
	linux-input@vger.kernel.org, letux-kernel@openphoenux.org,
	kernel@pyra-handheld.com, Hartmut Knaack <knaack.h@gmx.de>,
	Lars-Peter Clausen <lars@metafoo.de>,
	Peter Meerwald-Stadler <pmeerw@pmeerw.net>,
	linux-kernel@vger.kernel.org, linux-iio@vger.kernel.org
Subject: Re: [RFC v2] iio: input-bridge: optionally bridge iio acceleometers to create a /dev/input interface
Date: Fri, 10 May 2019 12:06:03 +0200	[thread overview]
Message-ID: <4C600F37-33E3-4C3D-B7D1-BBB85D5A2195@goldelico.com> (raw)
In-Reply-To: <4a77d53966d117bc5c7ff2836634d8591633f4f5.camel@hadess.net>

> Am 10.05.2019 um 11:35 schrieb Bastien Nocera <hadess@hadess.net>:
> 
> On Fri, 2019-05-10 at 11:33 +0200, H. Nikolaus Schaller wrote:
>>> 
> <snip>
>> It does through "Input device name:" starting with "iio-bridge:" as
>> you can see in the commit message of [RFC v3]:
> 
> This makes it ABI, right?

The "Input device name:" is already ABI of the input system (although I guess the string is
built into the evtest tool). I think there are also /sys nodes which carry the same information.

But yes, if someone changes the "iio-bridge:" prefix in kernel code it breaks a user space lib
making use of it:

+	poll_dev->input->name = kasprintf(GFP_KERNEL, "iio-bridge: %s",
+						    indio_dev->name);
+	poll_dev->input->phys = kasprintf(GFP_KERNEL, "iio:device%d",
+						    indio_dev->id);

This type of exporting names seems to be quite common. E.g. "mmcblk0p1" which may end up
in some /etc/fstab.

> 
> Big fat warnings around the code that declares it would be appreciated.

Ok.