> Because otherwise sendfile() fails with EAGAIN many times before
> sending any actual data.
EAGAIN on a blocking fd? Is it documented somewhere?
The Linux man page for sendfile() says:
EAGAIN Nonblocking I/O has been selected using O_NONBLOCK and the
write would block.
FreeBSD apparently says something similar:
[EAGAIN] The socket is marked for non-blocking I/O and not all
data was sent due to the socket buffer being filled.
If specified, the number of bytes successfully sent
will be returned in *sbytes.