Device file not appearing

[Gregory Anders]

On Wed, 17 Mar 2021 18:15:27 +0100, Greg KH <greg at kroah.com> wrote:
>Looks like you have mounted tmpfs on top of devtmpfs, which seems very
>odd.  Try unmounting the tmpfs instance and see if the node really is
>there in devtmpfs.
>
>Or better yet, mount devtmpfs somewhere else right now to see if the
>node is there.
>
>Good luck with your userspace mount maze!
>
>greg k-h

Ok I finally tracked down what was going on. The embedded distribution I 
am using uses mdev. mdev has an init script that mounts tmpfs on /dev, 
which is why devtmpfs wasn't working as expected.

mdev requires the kernel option CONFIG_UEVENT_HELPER=y which was not 
enabled in my configuration (it even has a scary help description, 
something along the lines of "this should not be used", so I didn't 
think to enable it until I saw it mentioned somewhere else). After 
enabling that, the device file appears under /dev.

Thanks for your help Greg!