[Libguestfs] [PATCH libnbd 2/2] api: Implement local command with systemd socket activation.

[Eric Blake]

On 9/26/19 11:40 AM, Richard W.M. Jones wrote:
> This adds new APIs for running a local NBD server and connecting to it
> using systemd socket activation (instead of stdin/stdout).
> 
> This includes interop tests against nbdkit and qemu-nbd which I
> believe are the only NBD servers supporting socket activation.  (If we
> find others then we can add more interop tests in future.)
> 
> The upstream spec for systemd socket activation is here:
> http://0pointer.de/blog/projects/socket-activation.html
> ---

> +
> +  /* Use /tmp instead of TMPDIR because we must ensure the path is
> +   * short enough to store in the sockaddr_un.  On some platforms this
> +   * may cause problems so we may need to revisit it.  XXX
> +   */
> +  h->sa_tmpdir = strdup ("/tmp/libnbdXXXXXX");
> +  h->sa_sockpath = strdup ("/tmp/libnbdXXXXXX/sock");
> +  if (h->sa_tmpdir == NULL || h->sa_sockpath == NULL) {
> +    SET_NEXT_STATE (%.DEAD);
> +    set_error (errno, "strdup");
> +    return 0;
> +  }
> +
> +  if (mkdtemp (h->sa_tmpdir) == NULL) {
> +    SET_NEXT_STATE (%.DEAD);
> +    set_error (errno, "mkdtemp");
> +    return 0;
> +  }
> +  len = strlen (h->sa_tmpdir);
> +  memcpy (h->sa_sockpath, h->sa_tmpdir, len);
> +
> +  s = socket (AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
> +  if (s == -1) {
> +    SET_NEXT_STATE (%.DEAD);
> +    set_error (errno, "socket");
> +    return 0;
> +  }
> +
> +  addr.sun_family = AF_UNIX;
> +  memcpy (addr.sun_path, h->sa_sockpath, strlen (h->sa_sockpath) + 1);

What if we used the abstract socket namespace instead?  Then we don't 
have to worry about mkdtmp or cleanup of the socket file.  True, that 
may only work on Linux, but we could add an API to query if we support 
socket activation (true on Linux, false on BSD)...


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org