[PATCH 1/3] os: Add -displayfd option.

[Adam Jackson]

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 at redhat.com>
---
 dix/globals.c       |    1 +
 doc/man/Xserver.man |    7 +++++
 include/opaque.h    |    1 +
 os/connection.c     |   72 ++++++++++++++++++++++++++++++++++----------------
 os/utils.c          |   11 ++++++++
 5 files changed, 69 insertions(+), 23 deletions(-)

diff --git a/dix/globals.c b/dix/globals.c
index 0a6b170..0ee83c0 100644
--- a/dix/globals.c
+++ b/dix/globals.c
@@ -126,6 +126,7 @@ int defaultColorVisualClass = -1;
 int monitorResolution = 0;
 
 char *display;
+int displayfd;
 char *ConnectionInfo;
 
 CARD32 TimeOutValue = DEFAULT_TIMEOUT * MILLI_PER_SECOND;
diff --git a/doc/man/Xserver.man b/doc/man/Xserver.man
index b725949..5e599be 100644
--- a/doc/man/Xserver.man
+++ b/doc/man/Xserver.man
@@ -121,6 +121,13 @@ Not obeyed by all servers.
 .B \-core
 causes the server to generate a core dump on fatal errors.
 .TP 8
+.B \-displayfd \fIfd\fP
+specifies a file descriptor in the launching process.  Rather than specify
+a display number, the X server will attempt to listen on successively higher
+display numbers, and upon finding a free one, will write the port number back
+on this file descriptor as a newline-terminated string.  The \-pn option is
+ignored when using \-displayfd.
+.TP 8
 .B \-deferglyphs \fIwhichfonts\fP
 specifies the types of fonts for which the server should attempt to use
 deferred glyph loading.  \fIwhichfonts\fP can be all (all fonts),
diff --git a/include/opaque.h b/include/opaque.h
index 5c70717..f23203f 100644
--- a/include/opaque.h
+++ b/include/opaque.h
@@ -50,6 +50,7 @@ extern _X_EXPORT int ScreenSaverAllowExposures;
 extern _X_EXPORT int defaultScreenSaverBlanking;
 extern _X_EXPORT int defaultScreenSaverAllowExposures;
 extern _X_EXPORT char *display;
+extern _X_EXPORT int displayfd;
 
 extern _X_EXPORT int defaultBackingStore;
 extern _X_EXPORT Bool disableBackingStore;
diff --git a/os/connection.c b/os/connection.c
index 5580fab..8fb8c36 100644
--- a/os/connection.c
+++ b/os/connection.c
@@ -145,6 +145,7 @@ Bool AnyClientsWriteBlocked;	/* true if some client blocked on write */
 static Bool RunFromSmartParent;	/* send SIGUSR1 to parent process */
 Bool RunFromSigStopParent;	/* send SIGSTOP to our own process; Upstart (or
 				   equivalent) will send SIGCONT back. */
+static char dynamic_display[7];
 Bool PartialNetwork;	/* continue even if unable to bind all addrs */
 static Pid_t ParentProcess;
 
@@ -356,11 +357,25 @@ NotifyParentProcess(void)
 	    kill (ParentProcess, SIGUSR1);
 	}
     }
+    if (dynamic_display[0])
+	write(displayfd, dynamic_display, strlen(dynamic_display));
     if (RunFromSigStopParent)
 	raise (SIGSTOP);
 #endif
 }
 
+static Bool
+TryCreateSocket(int num, int *partial)
+{
+    char port[20];
+
+    sprintf(port, "%d", num);
+
+    return _XSERVTransMakeAllCOTSServerListeners(port, partial,
+						 &ListenTransCount,
+						 &ListenTransConns);
+}
+
 /*****************
  * CreateWellKnownSockets
  *    At initialization, create the sockets to listen on for new clients.
@@ -371,7 +386,6 @@ CreateWellKnownSockets(void)
 {
     int		i;
     int		partial;
-    char 	port[20];
 
     FD_ZERO(&AllSockets);
     FD_ZERO(&AllClients);
@@ -386,32 +400,44 @@ CreateWellKnownSockets(void)
 
     FD_ZERO (&WellKnownConnections);
 
-    sprintf (port, "%d", atoi (display));
-
-    if ((_XSERVTransMakeAllCOTSServerListeners (port, &partial,
-	&ListenTransCount, &ListenTransConns) >= 0) &&
-	(ListenTransCount >= 1))
+    if (display)
     {
-	if (!PartialNetwork && partial)
-	{
-	    FatalError ("Failed to establish all listening sockets");
-	}
-	else
+	if (TryCreateSocket(atoi(display), &partial) &&
+	    (ListenTransCount >= 1))
+	    if (!PartialNetwork && partial)
+		FatalError ("Failed to establish all listening sockets");
+    }
+    else /* -displayfd */
+    {
+	Bool found = 0;
+	for (i = 0; i < 65535 - 1024; i++)
 	{
-	    ListenTransFds = malloc(ListenTransCount * sizeof (int));
-
-	    for (i = 0; i < ListenTransCount; i++)
+	    if (!TryCreateSocket(i, &partial) && !partial)
 	    {
-		int fd = _XSERVTransGetConnectionNumber (ListenTransConns[i]);
-		
-		ListenTransFds[i] = fd;
-		FD_SET (fd, &WellKnownConnections);
-
-		if (!_XSERVTransIsLocal (ListenTransConns[i]))
-		{
-		    DefineSelf (fd);
-		}
+		found = 1;
+		break;
 	    }
+	    else
+		CloseWellKnownConnections();
+	}
+	if (!found)
+	    FatalError("Failed to find a socket to listen on");
+	sprintf(dynamic_display, "%d\n", i);
+	display = dynamic_display;
+    }
+
+    ListenTransFds = malloc (ListenTransCount * sizeof (int));
+
+    for (i = 0; i < ListenTransCount; i++)
+    {
+	int fd = _XSERVTransGetConnectionNumber (ListenTransConns[i]);
+
+	ListenTransFds[i] = fd;
+	FD_SET (fd, &WellKnownConnections);
+
+	if (!_XSERVTransIsLocal (ListenTransConns[i]))
+	{
+	    DefineSelf (fd);
 	}
     }
 
diff --git a/os/utils.c b/os/utils.c
index 18fd911..eb2fafe 100644
--- a/os/utils.c
+++ b/os/utils.c
@@ -671,6 +671,17 @@ 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 */ ;
-- 
1.7.3.4