Doesn't work with the newer kernels.
Used to work with linux-5.6.

Syscall definitions were changed to match those of the first task.
Getting multiple user entries is unsupported. Deliting multiple user entries is impossible as well.

For the syscalls to work properly:
-   tchardev module should be loaded;
-   it should be made accessible at path /dev/tchardev.
Otherwise, error codes are returned.

A program is provided to test the syscalls of the running kernel.
Its source code is testsyscalls.c file.
Its arguments (-g, -i, -d, et cetera) correspond to those of the character device.