os: Add -displayfd option

This option specifies a file descriptor in the launching process.  X
will scan for an available display number and write that number back to
the launching process, at the same time as SIGUSR1 generation.  This
means display managers don't need to guess at available display numbers.
As a consequence, if X fails to start when using -displayfd, it's not
because the display was in use, so there's no point in retrying the X
launch on a higher display number.

Signed-off-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Reviewed-by: Julien Cristau <jcristau@debian.org>
Tested-by: Julien Cristau <jcristau@debian.org>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/os/utils.c b/os/utils.c
index 30592d2cc..3a1ef9303 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -659,6 +659,15 @@ ProcessCommandLine(int argc, char *argv[])
             else
                 UseMsg();
         }
+        else if (strcmp(argv[i], "-displayfd") == 0) {
+            if (++i < argc) {
+                displayfd = atoi(argv[i]);
+                display = NULL;
+                nolock = TRUE;
+            }
+            else
+                UseMsg();
+        }
 #ifdef DPMSExtension
         else if (strcmp(argv[i], "dpms") == 0)
             /* ignored for compatibility */ ;