Hari Prashanth wrote: > Can you say me what address space is? Not the > address space associated with the user space. its the > other one. Hari, Every user-space process has a 4 gigabyte virtual memory address space (some CPUs allow for larger spaces). The kernel also has a single virtual memory address space for its own use -- it is also 4 GB in size. All kernel code runs in the kernel virtual memory address space. There are times, that the kernel virtual memory address space contains pieces of a user process's address space. This is so that system calls can access arguments passed using pointers. A classic example are the read() and write() system calls, which need to transfer data from kernel buffers into a user process address space. I think a common misconception held by people who are new to kernel programming is that the kernel always deals only with physical memory addresses. In fact, most kernel code uses virtual addresses within the kernel's own personal virtual memory space. -- Francis Litterio franl <at> world . std . com -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
