Doubt related to iovec/kvec for kernel_sendmsg()

Hi,

I have few doubts related to iovec & kvec structures, in particular
related to using these strucutes for sending the data over the socket
using kernel_sendmsg()/sock_sendmsg().

Doubts -
1) Can we pass iovec to kernel_sendmsg() instead of kvecs?  Is it
recommended to use kvec instead of iovec ?

2) What are differences between kvec vs iovec ?
From the definition of these structures, I see that iovec has _user
type, so it may point to a user buffer.  Are there some other
differences between kvec or iovec ?

3) When shall we use kvec instead of iovec ?

4) For iterating the iovecs, I could find one macro -- 'iov_for_each'
which uses iov_iterator.
Is there similar easy way to iterate the kvec ?

Thanks & Regards,
Suraj