linux-kernel - Re: [PATCH] iio: industrialio-core: look for aliases to request device index

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Message-ID: <CAMknhBHwVHOS742aVL-pmHzpheicb2=6Hi2Lgz0DvTcXcMoeCg@mail.gmail.com>
Date: Mon, 18 Mar 2024 09:55:18 -0500
From: David Lechner <dlechner@...libre.com>
To: Dominique Martinet <dominique.martinet@...ark-techno.com>
Cc: Jonathan Cameron <Jonathan.Cameron@...wei.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>, Jonathan Cameron <jic23@...nel.org>, 
	Syunya Ohshio <syunya.ohshio@...ark-techno.com>, Guido Günther <agx@...xcpu.org>, 
	Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh+dt@...nel.org>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, 
	linux-iio@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: industrialio-core: look for aliases to request
 device index

On Sun, Mar 17, 2024 at 9:15 PM Dominique Martinet
<dominique.martinet@...ark-techno.com> wrote:
>
> David Lechner wrote on Fri, Mar 15, 2024 at 10:53:36AM -0500:
> > How about using udev rules to create symlinks for each device based on
> > the label attribute? No changes to the kernel are needed.
>
> Right, it's definitely possible to make symlinks for each "device" -- my
> patch comment links to such an udev script "solution":
> https://git.toradex.com/cgit/meta-toradex-bsp-common.git/tree/recipes-core/udev/files/verdin-imx8mm/toradex-adc.sh?h=kirkstone-6.x.y
> (the script is launched by udev here:
> https://git.toradex.com/cgit/meta-toradex-bsp-common.git/tree/recipes-core/udev/files/verdin-imx8mm/99-toradex.rules
> )
>
> My conceptual problem with this is that this makes symlinks in /dev to
> files in /sys and it feels like we're crossing boundaries.
> As far as I can tell there is no way for userspace to create arbitrary
> symlinks in /sys, so I think we could have an interface more
> user-friendly by allowing paths to be static for users with multiple
> devices.

How about this: Use udev to create one symlink from /dev/frendly-name
to /dev/iio:deviceX. Then in your application, look up the device by
/dev/friendly-name. Then resolve the symlink to translate
friendly-name to iio:deviceX. Now your app has the correct iio:deviceX
and can use /sys/bus/iio/devices/iio:deviceX/ directly instead of
making any symlinks to sysfs.