io_fd_canwrite - prepare descriptor for io_wait

       io_fd_canwrite  is  just  like io_fd, except that it assumes the descriptor is writable, which may save a
       syscall or two.  This assumption is true in most cases, because the kernel  buffers  writes.   Noteworthy
       cases  in  which  you  need to use io_fd instead of io_fd_canwrite are unconnected sockets, i.e. when you
       queued a non-blocking connect() and want to ask for writability to get notified when it went through.

       It is OK to call this function on a descriptor that io_fd() has already been called on.

       io_fd_canwrite - prepare descriptor for io_wait

       io_fd_canwrite returns 1 on success, 0 on error.

io_wait(3), io_wantread(3), io_canread(3), io_eagain(3), io_nonblock(3), io_fd(3)

                                                                                               io_fd_canwrite(3)

#include<libowfat/io.h>

       int io_fd(int64 fd); int io_fd_canwrite(int64 fd);