Re: [PATCH v11 0/6] MR2786: Add support for AF_UNIX sockets

[Chip Davis (＠cdavis5e)]

Chip Davis (@cdavis5e) commented about server/fd.c:
>              fd->unix_fd = open( name, O_RDONLY | (flags & ~(O_TRUNC | O_CREAT | O_EXCL)), *mode );
>      }
>
> -
>    /* open(3) throws ENXIO when `path` is one of:
> -
>     * 1. a FIFO, and open(3) is called with O_WRONLY | O_NONBLOCK,
> -
>     *    and no other process is currently attempting to read from `path`.
> -
>     * 2. a special device file, and the device it corresponds to does not exist.
> -
>     * 3. a UNIX socket.

Not all systems fail that way when `open(2)`ing a local-domain socket file. According to [POSIX](https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html), the `errno` is supposed to be `EOPNOTSUPP` in that case; in this regard, the Linux behavior is nonstandard. Some implementations may actually let you `open(2)` a socket file under certain circumstances.