Adeos's role w.r.t Linux

Question

The event pipeline The fundamental Adeos structure one must keep in mind is the chain of client domains asking for event control. A domain is a kernelbased software component which can ask the Adeos layer to be notified of:
· Every incoming external interrupt, or autogenerated virtual interrupt; ·
Every system call issued by Linux applications, ·
Other system events triggered by the kernel code (e.g. Linux task switching, signal notification, Linux task exits etc.).

From: Life with Adeos: http://www.xenomai.org/documentation/xenomai-2.4/pdf/Life-with-Adeos-rev-B.pdf

Question: Adeos is supposed to be between the hardware and the Linux kernel, I can understand about Adeos telling the Linux about hardware interrupts but Why should Adeos know about the "system call" issued by Linux?

Answer 1

Linux system calls offer direct access to hardware in some cases. E.g. read() and write() can be applied to raw devices in /dev, ioctl() can be used to poke values into hardware registers. I assume it is simpler to intercept such activities at syscall time than to anticipate everything a device driver might do and infest it with callbacks.