Accessing Data from a Kernel Process

Because kernel processes execute in the more privileged kernel protection domain, a kernel process can access data that user processes cannot.

This applies to all kernel data, of which there are three general categories:

• The user block data structure

  The u-block (or u-area) structure exists for kernel processes and contains roughly the same information for kernel processes as for user-mode processes. A kernel process must use kernel services to query or manipulate data from the u-area to maintain modularity and increase portability of code to other platforms.

• The stack for a kernel process

  To ensure binary compatibility with older applications, each kernel process has a stack called the process stack. This stack is used by the process initial thread.

  The location of the stack for a kernel process is implementation-dependent. This stack can be located in global memory or in the process-private segment of the kernel process. A kernel process must not assume automatically that its stack is located in global memory.

• Global kernel memory

  A kernel process can also access global kernel memory as well as allocate and de-allocate memory from the kernel heaps. Because it runs in the kernel protection domain, a kernel process can access any valid memory location within the global kernel address space. Memory dynamically allocated from the kernel heaps by the kernel process must be freed by the kernel process before exiting. Unlike user-mode processes, memory that is dynamically allocated by a kernel process is not freed automatically upon process exit.