Kernel: Do not use global variable as possible as you can try not to use global variables

And userspaceProgramYou must always consider using global variables with caution.

More intense kernel concurrency, multi-CPU operations, concurrent operations on multiple drivers, a carelessness may lead to a global variable uption.

In particular, when multiple devices use the same driver, this driver has multiple instances. At this time, the use of global variables will inevitably require consideration of the lock issue.

You can try to put the variables into the driver's private structure, which is much better. You only need to consider whether multiple CPUs will operate simultaneously.

In the userspace program, for example, when writing gstreamer plugin, global variables are also absolutely forbidden, because your Plugin may appear multiple times in a pipeline and thus have multiple instances.