Re: [PATCH 1/2] virdevmapper: Don't error on kernels without DM support

As promised yesterday, I've dived into the code and found out that the major number can be specified as a parameter to the dm module (just tested and it works). So the next thing I tried was to see how could we check whether the module was reloaded. I've tried opening /dev/mapper/control hoping that I will get EOF on module unload (which I could then use to run a callback that would invalidate the cached value). But having the file open prevents unloading the module. Loading/unloading a module results in an udev event, BUT we listen for udev events only in nodedev driver and moving the code out to a driver agnostic location and making it driver agnostic is too much code for a little gain. Then I looked whether it's possible to get the major number via an ioctl(). But haven't found anything. Hence, I think the best solution for us is to not cache anything and simply parse /proc/devices every time. As an optimization, I can firstly check whether /dev/mapper/control exists at all an if not exit early.