Re: Real-Time Preemption and UML?

[Esben Nielsen]

Well, I keep trying a little bit more. In the mean while you can get some
of the stuff I needed to change to at least get it to compile:

One of the problems was use of direct architecture specific semaphores
(which doesn't work under PREEMPT_REALTIME) and in places where a quick
(maybe too quick) look at the code told me that completions ought to be
used. Therefore I changed two semaphores to completions which compiled
fine. I have tried the change on 2.6.11-rc2, and it seemed to work, but I
have not tested it heavily.

The patch is in an attachment - I hope the mail-list will alow that. It is
simply too trouplesome otherwise when I am using Pine as mail client.

Esben


On Mon, 7 Feb 2005, Jeff Dike wrote:

> simlo@xxxxxxxxxx said:
> > Hi, I am trying to compile and run UM-Linux with PREEMPT_REALTIME. I
> > managed to get it to compile but it wont start - it simply stops
> > somewhere in start_kernel() :-( 
> 
> I've never played with preemption on UML.  No doubt it needs some work...
> 
> 				Jeff
> 
> -
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--- linux-2.6.11-rc2-um/arch/um/drivers/port_kern.c.orig	2005-01-23 15:53:29.000000000 +0100
+++ linux-2.6.11-rc2-um/arch/um/drivers/port_kern.c	2005-02-06 19:54:52.000000000 +0100
@@ -23,7 +23,7 @@
 struct port_list {
 	struct list_head list;
 	int has_connection;
-	struct semaphore sem;
+	struct completion done;
 	int port;
 	int fd;
 	spinlock_t lock;
@@ -66,7 +66,7 @@
 	conn->fd = fd;
 	list_add(&conn->list, &conn->port->connections);
 
-	up(&conn->port->sem);
+	complete(&conn->port->done);
 	return(IRQ_HANDLED);
 }
 
@@ -183,13 +183,14 @@
 	*port = ((struct port_list) 
 		{ .list 	 	= LIST_HEAD_INIT(port->list),
 		  .has_connection 	= 0,
-		  .sem 			= __SEMAPHORE_INITIALIZER(port->sem, 
-								  0),
 		  .lock 		= SPIN_LOCK_UNLOCKED,
 		  .port 	 	= port_num,
 		  .fd  			= fd,
 		  .pending 		= LIST_HEAD_INIT(port->pending),
 		  .connections 		= LIST_HEAD_INIT(port->connections) });
+
+	init_completion(&port->done), 
+
 	list_add(&port->list, &ports);
 
  found:
@@ -221,7 +222,7 @@
 	int fd;
 
 	while(1){
-		if(down_interruptible(&port->sem))
+		if(wait_for_completion_interruptible(&port->done))
 			return(-ERESTARTSYS);
 
 		spin_lock(&port->lock);
--- linux-2.6.11-rc2-um/arch/um/drivers/xterm_kern.c.orig	2005-01-23 15:53:29.000000000 +0100
+++ linux-2.6.11-rc2-um/arch/um/drivers/xterm_kern.c	2005-02-06 19:54:58.000000000 +0100
@@ -16,7 +16,7 @@
 #include "xterm.h"
 
 struct xterm_wait {
-	struct semaphore sem;
+	struct completion ready;
 	int fd;
 	int pid;
 	int new_fd;
@@ -32,7 +32,7 @@
 		return(IRQ_NONE);
 
 	xterm->new_fd = fd;
-	up(&xterm->sem);
+	complete(&xterm->ready);
 	return(IRQ_HANDLED);
 }
 
@@ -49,10 +49,10 @@
 
 	/* This is a locked semaphore... */
 	*data = ((struct xterm_wait) 
-		{ .sem  	= __SEMAPHORE_INITIALIZER(data->sem, 0),
-		  .fd 		= socket,
+		{ .fd 		= socket,
 		  .pid 		= -1,
 		  .new_fd 	= -1 });
+	init_completion(&data->ready);
 
 	err = um_request_irq(XTERM_IRQ, socket, IRQ_READ, xterm_interrupt, 
 			     SA_INTERRUPT | SA_SHIRQ | SA_SAMPLE_RANDOM, 
@@ -68,7 +68,7 @@
 	 *
 	 * XXX Note, if the xterm doesn't work for some reason (eg. DISPLAY
 	 * isn't set) this will hang... */
-	down(&data->sem);
+	wait_for_completion(&data->ready);
 
 	free_irq_by_irq_and_dev(XTERM_IRQ, data);
 	free_irq(XTERM_IRQ, data);