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How do I transfer data from kernel space to user space?
The function copy_to_user is used to copy data from the kernel address space to the address space of the user program. For example, to copy a buffer which has been allocated with kmalloc to the buffer provided by the user.
What is the primary method for passing data from user space to kernel space in AC program?
For any system, privilege mode and non-privilege mode is important for access protection. The processor must have hardware support for user/kernel mode. System Call Interfaces (SCI) are the only way to transit from User space to kernel space.
What is kernel space VS user space?
Kernel space is strictly reserved for running a privileged operating system kernel, kernel extensions, and most device drivers. In contrast, user space is the memory area where application software and some drivers execute.
What is Access_ok?
The access_ok() checks ensure that the userspace application isn’t asking the kernel to read from or write to kernel addresses (they’re an integrity/security check). Additionally, calling access_ok() with VERIFY_WRITE implies VERIFY_READ , so if you check the former you do not need to also check the latter.
What is Get_user_pages?
get_user_pages is typically used for fewer-copy IO operations, to get a handle on the memory by some means other than accesses via the user virtual addresses. The pages may be submitted for DMA to devices or accessed via their kernel linear mapping (via the kmap APIs).
Do system programs run in kernel space?
The kernel is the core of the operating system. It normally has full access to all memory and machine hardware (and everything else on the machine). To keep the machine as stable as possible, you normally want only the most trusted, well-tested code to run in kernel mode/kernel space.
What is the difference between user and kernel processes?
The system is in user mode when the operating system is running a user application such as handling a text editor. The transition from user mode to kernel mode occurs when the application requests the help of operating system or an interrupt or a system call occurs.
What is Copy_to_user in Linux?
The copy_to_user function copies a block of data from the kernel into user space. This function accepts a pointer to a user space buffer, a pointer to a kernel buffer, and a length defined in bytes. The function returns zero on success or non-zero to indicate the number of bytes that weren’t transferred.