Is kernel module necessary?
Modules are pieces of code that can be loaded and unloaded into the kernel upon demand. They extend the functionality of the kernel without the need to reboot the system. Without modules, we would have to build monolithic kernels and add new functionality directly into the kernel image.
What is the relation between system call user and kernel?
A system call is the way you transition between the application (“user mode”) and the kernel. Syscalls are slower than normal function calls, but newer x86 chips from Intel and AMD have a special sysenter / syscall opcode to make it take just a hundred nanoseconds or so, give or take.
What is the difference between kernel and device driver?
In general, drivers provide detail implementation to specific physical or logical devices, while kernel then provide a set of interface for drivers, and manage them in a higher abstracted level (HAL). By the way, kernel does a lot more than managing hardware resources.
What are the advantages of using loadable kernel modules?
Loadable kernel modules have several advantages over monolithic “blobs” of code in the kernel: * Device drivers don’t have to be hard-coded into the kernel. For example, if a new chip-set comes out that powers many webcams, that kernel module can simply be loaded instead of recompiling the kernel with the new module.
Why are system calls executed in kernel mode?
Check for invalid pointers. Since system calls are executed in kernel mode, they have access to kernel space and if pointers are not properly checked user applications might get read or write access to kernel space. For example, lets consider the case where such a check is not made for the read or write system calls.
Are there virtual system calls in the Linux kernel?
An interesting development of the VDSO are the virtual system calls (vsyscalls) which run directly from user space. These vsyscalls are also part of VDSO and they are accessing data from the VDSO page that is either static or modified by the kernel in a separate read-write map of the VDSO page.
Does a user program always use system calls to access a.?
However, it is possible to create userspace drivers that are built on top of some kernel one, although in the end they must make system calls to operate. This is possible with, e.g., I 2 C devices; the userspace driver uses the kernel’s SMBus API (which is all system calls).
Why do pointers have access to the kernel?
Pointers have a few important special cases that must be checked: Since system calls are executed in kernel mode, they have access to kernel space and if pointers are not properly checked user applications might get read or write access to kernel space.