[Spice-devel] [vdagent] Make sure the child is able to connect to the X server before exiting the mainline.

[Alon Levy]

On 06/24/2014 12:05 AM, Jeremy White wrote:
> This allows the vdagent to be used in the Xsetup phase of an xdm session;
> otherwise, its X11 connection fails because of the greeter display grab.

But could you make the comment contain the discussion where you
explained this in more detail?

> 
> Signed-off-by: Jeremy White <jwhite at codeweavers.com>
> ---
>  src/vdagent.c |   50 ++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 44 insertions(+), 6 deletions(-)
> 
> diff --git a/src/vdagent.c b/src/vdagent.c
> index d7f7aba..905ff5b 100644
> --- a/src/vdagent.c
> +++ b/src/vdagent.c
> @@ -35,6 +35,7 @@
>  #include <sys/stat.h>
>  #include <spice/vd_agent.h>
>  #include <glib.h>
> +#include <poll.h>
>  
>  #include "udscs.h"
>  #include "vdagentd-proto.h"
> @@ -151,9 +152,34 @@ static void quit_handler(int sig)
>      quit = 1;
>  }
>  
> -void daemonize(void)
> +/* When we daemonize, it is useful to have the main process
> +   wait to make sure the X connection worked.  We wait up
> +   to 10 seconds to get an 'all clear' from the child
> +   before we exit.  If we don't, we're able to exit with a
> +   status that indicates an error occured */
> +void wait_and_exit(int s)
>  {
> -    int x, retval = 0;
> +    char buf[4];
> +    struct pollfd p;
> +    p.fd = s;
> +    p.events = POLLIN;
> +
> +    if (poll(&p, 1, 10000) > 0)
> +        if (read(s, buf, sizeof(buf)) > 0)
> +            exit(0);
> +
> +    exit(1);
> +}
> +
> +int daemonize(void)
> +{
> +    int x;
> +    int fd[2];
> +
> +    if (socketpair(PF_LOCAL, SOCK_STREAM, 0, fd)) {
> +        syslog(LOG_ERR, "socketpair : %s", strerror(errno));
> +        exit(1);
> +    }
>  
>      /* detach from terminal */
>      switch (fork()) {
> @@ -161,13 +187,17 @@ void daemonize(void)
>          close(0); close(1); close(2);
>          setsid();
>          x = open("/dev/null", O_RDWR); x = dup(x); x = dup(x);
> -        break;
> +        close(fd[0]);
> +        return fd[1];
>      case -1:
>          syslog(LOG_ERR, "fork: %s", strerror(errno));
> -        retval = 1;
> +        exit(1);
>      default:
> -        exit(retval);
> +        close(fd[1]);
> +        wait_and_exit(fd[0]);
>      }
> +
> +    return 0;
>  }
>  
>  static int file_test(const char *path)
> @@ -182,6 +212,7 @@ int main(int argc, char *argv[])
>      fd_set readfds, writefds;
>      int c, n, nfds, x11_fd;
>      int do_daemonize = 1;
> +    int parent_socket = 0;
>      int x11_sync = 0;
>      struct sigaction act;
>  
> @@ -236,7 +267,7 @@ int main(int argc, char *argv[])
>      }
>  
>      if (do_daemonize)
> -        daemonize();
> +        parent_socket = daemonize();
>  
>  reconnect:
>      if (version_mismatch) {
> @@ -275,6 +306,13 @@ reconnect:
>      vdagent_file_xfers = vdagent_file_xfers_create(client, fx_dir,
>                                                     fx_open_dir, debug);
>  
> +    if (parent_socket) {
> +        if (write(parent_socket, "OK", 2) != 2)
> +            syslog(LOG_WARNING, "Parent already gone.");
> +        close(parent_socket);
> +        parent_socket = 0;
> +    }
> +
>      while (client && !quit) {
>          FD_ZERO(&readfds);
>          FD_ZERO(&writefds);
>