Entry points: userland process All the userland->kernel accesses have to take place via a system call. To do this the program calls some architecture specific code in libc and the kernel. Copy the arguments into kernel address space Run handling code for that particular interrupt number Copy result back into user process Errors are returned in errno. Many of the file related system calls are relevant for some drivers with /dev entries. Each /dev entry has major (device type) and minor (unit number) with the major number mapping being machine dependent. arch/myarch/myarch/conf.c contains the mapping table. Device drivers with /dev entries generally have to manage queues of access usually in a strategy() function.