Add a new syscall

Adding a new syscall in the kernel is easy.

There are 3 steps.

1. Add new syscall number for the new syscall in header/src/lib.rs.

pub enum NR {
    Read,
}

2. Implement the new syscall in kernel/src/syscall_handlers/mod.rs.

This is generally done via define_syscall_handler! if the syscall is trivial. For example

define_syscall_handler!(
read(fd: i32, buf: *mut i8, len: usize) -> c_long {
    // Implement your vfs read.
});

3. Register the new syscall in kernel/src/syscall_handlers/mod.rs.

Add a new entry in syscall_table!. For example,

(Read, read),

Must be noted, the first operand MUST be the unqualified name of the NR enumeration.