1 files changed, 61 insertions, 20 deletions

diff --git a/arch/um/drivers/chan_kern.c b/arch/um/drivers/chan_kern.c
index 37538b4168da..e78a99816c86 100644
--- a/arch/um/drivers/chan_kern.c
+++ b/arch/um/drivers/chan_kern.c
@@ -81,6 +81,12 @@ static const struct chan_ops not_configged_ops = {
 };
 #endif /* CONFIG_NOCONFIG_CHAN */
 
+static inline bool need_output_blocking(void)
+{
+	return time_travel_mode == TT_MODE_INFCPU ||
+	       time_travel_mode == TT_MODE_EXTERNAL;
+}
+
 static int open_one_chan(struct chan *chan)
 {
 	int fd, err;
@@ -96,15 +102,43 @@ static int open_one_chan(struct chan *chan)
 		return fd;
 
 	err = os_set_fd_block(fd, 0);
-	if (err) {
-		(*chan->ops->close)(fd, chan->data);
-		return err;
-	}
+	if (err)
+		goto out_close;
+
+	chan->fd_in = fd;
+	chan->fd_out = fd;
+
+	/*
+	 * In time-travel modes infinite-CPU and external we need to guarantee
+	 * that any writes to the output succeed immdiately from the point of
+	 * the VM. The best way to do this is to put the FD in blocking mode
+	 * and simply wait/retry until everything is written.
+	 * As every write is guaranteed to complete, we also do not need to
+	 * request an IRQ for the output.
+	 *
+	 * Note that input cannot happen in a time synchronized way. We permit
+	 * it, but time passes very quickly if anything waits for a read.
+	 */
+	if (chan->output && need_output_blocking()) {
+		err = os_dup_file(chan->fd_out);
+		if (err < 0)
+			goto out_close;
 
-	chan->fd = fd;
+		chan->fd_out = err;
+
+		err = os_set_fd_block(chan->fd_out, 1);
+		if (err) {
+			os_close_file(chan->fd_out);
+			goto out_close;
+		}
+	}
 
 	chan->opened = 1;
 	return 0;
+
+out_close:
+	(*chan->ops->close)(fd, chan->data);
+	return err;
 }
 
 static int open_chan(struct list_head *chans)
@@ -125,7 +159,7 @@ static int open_chan(struct list_head *chans)
 void chan_enable_winch(struct chan *chan, struct tty_port *port)
 {
 	if (chan && chan->primary && chan->ops->winch)
-		register_winch(chan->fd, port);
+		register_winch(chan->fd_in, port);
 }
 
 static void line_timer_cb(struct work_struct *work)
@@ -156,8 +190,9 @@ int enable_chan(struct line *line)
 
 		if (chan->enabled)
 			continue;
-		err = line_setup_irq(chan->fd, chan->input, chan->output, line,
-				     chan);
+		err = line_setup_irq(chan->fd_in, chan->input,
+				     chan->output && !need_output_blocking(),
+				     line, chan);
 		if (err)
 			goto out_close;
 
@@ -196,7 +231,8 @@ void free_irqs(void)
 
 		if (chan->input && chan->enabled)
 			um_free_irq(chan->line->read_irq, chan);
-		if (chan->output && chan->enabled)
+		if (chan->output && chan->enabled &&
+		    !need_output_blocking())
 			um_free_irq(chan->line->write_irq, chan);
 		chan->enabled = 0;
 	}
@@ -216,15 +252,19 @@ static void close_one_chan(struct chan *chan, int delay_free_irq)
 	} else {
 		if (chan->input && chan->enabled)
 			um_free_irq(chan->line->read_irq, chan);
-		if (chan->output && chan->enabled)
+		if (chan->output && chan->enabled &&
+		    !need_output_blocking())
 			um_free_irq(chan->line->write_irq, chan);
 		chan->enabled = 0;
 	}
+	if (chan->fd_out != chan->fd_in)
+		os_close_file(chan->fd_out);
 	if (chan->ops->close != NULL)
-		(*chan->ops->close)(chan->fd, chan->data);
+		(*chan->ops->close)(chan->fd_in, chan->data);
 
 	chan->opened = 0;
-	chan->fd = -1;
+	chan->fd_in = -1;
+	chan->fd_out = -1;
 }
 
 void close_chan(struct line *line)
@@ -244,7 +284,7 @@ void close_chan(struct line *line)
 void deactivate_chan(struct chan *chan, int irq)
 {
 	if (chan && chan->enabled)
-		deactivate_fd(chan->fd, irq);
+		deactivate_fd(chan->fd_in, irq);
 }
 
 int write_chan(struct chan *chan, const u8 *buf, size_t len, int write_irq)
@@ -254,7 +294,7 @@ int write_chan(struct chan *chan, const u8 *buf, size_t len, int write_irq)
 	if (len == 0 || !chan || !chan->ops->write)
 		return 0;
 
-	n = chan->ops->write(chan->fd, buf, len, chan->data);
+	n = chan->ops->write(chan->fd_out, buf, len, chan->data);
 	if (chan->primary) {
 		ret = n;
 	}
@@ -268,7 +308,7 @@ int console_write_chan(struct chan *chan, const char *buf, int len)
 	if (!chan || !chan->ops->console_write)
 		return 0;
 
-	n = chan->ops->console_write(chan->fd, buf, len);
+	n = chan->ops->console_write(chan->fd_out, buf, len);
 	if (chan->primary)
 		ret = n;
 	return ret;
@@ -296,14 +336,14 @@ int chan_window_size(struct line *line, unsigned short *rows_out,
 	if (chan && chan->primary) {
 		if (chan->ops->window_size == NULL)
 			return 0;
-		return chan->ops->window_size(chan->fd, chan->data,
+		return chan->ops->window_size(chan->fd_in, chan->data,
 					      rows_out, cols_out);
 	}
 	chan = line->chan_out;
 	if (chan && chan->primary) {
 		if (chan->ops->window_size == NULL)
 			return 0;
-		return chan->ops->window_size(chan->fd, chan->data,
+		return chan->ops->window_size(chan->fd_in, chan->data,
 					      rows_out, cols_out);
 	}
 	return 0;
@@ -319,7 +359,7 @@ static void free_one_chan(struct chan *chan)
 		(*chan->ops->free)(chan->data);
 
 	if (chan->primary && chan->output)
-		ignore_sigio_fd(chan->fd);
+		ignore_sigio_fd(chan->fd_in);
 	kfree(chan);
 }
 
@@ -478,7 +518,8 @@ static struct chan *parse_chan(struct line *line, char *str, int device,
 				 .output 	= 0,
 				 .opened  	= 0,
 				 .enabled  	= 0,
-				 .fd 		= -1,
+				 .fd_in		= -1,
+				 .fd_out	= -1,
 				 .ops 		= ops,
 				 .data 		= data });
 	return chan;
@@ -549,7 +590,7 @@ void chan_interrupt(struct line *line, int irq)
 			schedule_delayed_work(&line->task, 1);
 			goto out;
 		}
-		err = chan->ops->read(chan->fd, &c, chan->data);
+		err = chan->ops->read(chan->fd_in, &c, chan->data);
 		if (err > 0)
 			tty_insert_flip_char(port, c, TTY_NORMAL);
 	} while (err > 0);