FreeBSD 11 sendfile checks the file descriptor first, then looks up the
socket with getsock_cap, which answers ENOTSOCK for an open descriptor
that is not a socket and EBADF for one that is not open
(sys/kern/kern_sendfile.c, sys/kern/uipc_syscalls.c).
sendfile replaced the errno that Lookup had already set with EBADF. It
now reports the errno Lookup chose, so an open non-socket gives ENOTSOCK
and a closed descriptor still gives EBADF. The sentence about this gap
is cut from the sendfile debt entry and guest_sendfile covers both cases.
PS5MC (PPSA99420) stops at start-up on sendfile. It follows FreeBSD 11:
headers, the file range and trailers go to a connected stream socket, the
file offset does not move, a non-blocking socket fails with EAGAIN after
a partial send, and *sbytes reports what was sent. The checks and the
point where *sbytes is written follow kern_sendfile.c.
Retr0