OS//syscall

A system call (syscall) is the controlled gate, kept by the kernel, between user space and kernel space: an OS process uses it whenever it needs hardware access, to read a file, send a packet or allocate memory.

A system call (syscall) is the controlled gate, kept by the kernel, between user space and kernel space: an OS process uses it whenever it needs hardware access, to read a file, send a packet or allocate memory.

1The process traps into the kernelsyscall instruction2The kernel validates the arguments3The kernel performs the operation4The kernel returns to the process

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