Setup a btrfs subvolume on a btrfs partition and mount it on some directory. Then compile and run this program:

#include <iostream>
#include <solid/device.h>
#include <solid/storageaccess.h>

int main(int argc, char **argv) 
{
	QList<Solid::Device> devs = Solid::Device::listFromType(Solid::DeviceInterface::StorageAccess);
	foreach (Solid::Device dev,devs)
	{
		Solid::StorageAccess* sa = dev.as<Solid::StorageAccess>();
		if(!sa->filePath().isEmpty())
			std::cout << "StorageAccess: " << sa->filePath().toLocal8Bit().data() << std::endl;
	}
    return 0;
}

The result is that the  mount point of the mounted btrfs subvolume is not printed to the standard output. So it seems that btrfs subvolumes are not handled wel in solid.

This problem is the root cause of https://bugs.kde.org/show_bug.cgi?id=306825

Reproducible: Always