sysfs: pass function pointers to kernel (not just a value through attribute)

Hello everyone, I am looking for some mechanism for userspace tasks to pass certain functions to kernel and let the kernel execute these functions on behalf of userspace tasks. I know that sysfs can be used with kobject embedded into internal kernel structure to access kernel variables. But is there anyway for userspace tasks to pass a function to kernel to execute through sysfs? PS: adding syscall in the kernel can certainly satisfy my needs but it is less favorable because the new kernel service I want to add is not that general to be added as a new syscall. Thanks in advance! T