On 02/04/2017 04:03 AM, Richard W.M. Jones wrote: > Socket activation (sometimes known as systemd socket activation) > allows an Internet superserver to pass a pre-opened listening socket > to the process, instead of having qemu-nbd open a socket itself. This > is done via the LISTEN_FDS and LISTEN_PID environment variables, and a > standard file descriptor range. > > This change partially implements socket activation for qemu-nbd. If > the environment variables are set correctly, then socket activation > will happen automatically, otherwise everything works as before. The > limitation is that LISTEN_FDS must be 1. > > Signed-off-by: Richard W.M. Jones. > ---
> +
> + /* So the file descriptors don't leak into child processes. */
> + for (i = 0; i < nr_fds; ++i) {
> + fd = FIRST_SOCKET_ACTIVATION_FD + i;
> + if (fcntl(fd, F_SETFD, FD_CLOEXEC) == -1) {
This is not the right way to do things (it risks clearing any other FD_
flags currently set on the fd, even though there aren't any such FD_
flags in common use). You HAVE to do F_GETFD before F_SETFD
(read-modify-write) for correct usage - and the best way to do that is
to use qemu_set_cloexec() from util/oslib-posix.c.
Except that qemu_set_cloexec() doesn't pay attention to errors...
> + /* If we cannot set FD_CLOEXEC then it probably means the file
> + * descriptor is invalid, so socket activation has gone wrong
> + * and we should exit.
> + */
> + error_report("Socket activation failed: "
> + "invalid file descriptor fd = %d: %m",
> + fd);
...while you use it for argument validation. Hmm.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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