I/O//syscall

- A system call — the controlled gate between user space and kernel space

A system call — the controlled gate between user space and kernel space

When a process needs hardware access (read file, send packet, allocate memory), it traps into the kernel via a syscall instruction.

The kernel validates arguments, performs the operation, and returns.

Syscall overhead (context switch + TLB flush) motivates batching APIs (io_uring, sendmmsg) and DMA for bulk transfers.