Function sys_readv 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn sys_readv(
    fd: i32,
    iov: *const iovec,
    iovcnt: usize,
) -> isize

read() attempts to read nbyte of data to the object referenced by the descriptor fd from a buffer. read() performs the same action, but scatters the input data from the iovcnt buffers specified by the members of the iov array: iov[0], iov[1], ..., iov[iovcnt-1].

struct iovec {
    char   *iov_base;  /* Base address. */
    size_t iov_len;    /* Length. */
};

Each iovec entry specifies the base address and length of an area in memory from which data should be written. readv() will always fill an completely before proceeding to the next.