Re: Replacing global GPIO numbers in sysfs with hardware offsets

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Wed, Feb 26, 2025 at 1:43 PM Marek Vasut <marex@xxxxxxx> wrote:
>
> Can we really make do without export/unexport ?
>
> Consider this scenario:
>
> - User open()s and write()s /sys/bus/gpio/gpiochip0/gpio0/value
> - User keeps FD to /sys/bus/gpio/gpiochip0/gpio0/value open
> - Kernel module gets loaded, binds to DT node which references the same GPIO
> - User write()s /sys/bus/gpio/gpiochip0/gpio0/value open again
>
> I wonder if this could pose a problem ?
>
> I suspect the kernel module loading should fail , right ?

If the kernel module in question registers a driver that will bind to
a device which wants to request the same GPIO that sysfs already
holds, then gpiod_get() will fail with -EBUSY. In other words: even if
we drop export, there still has to be some way of "claiming" the
GPIOs. /sys/bus/gpio/gpiochip0/gpio0/request? I think I prefer
export/unexport.

Bartosz