linux-kernel - [047/121] virtio: console: return -ENODEV on all read operations after unplug

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Message-ID: <lsq.1378608721.402660700@decadent.org.uk>
Date:	Sun, 08 Sep 2013 03:52:01 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Amit Shah" <amit.shah@...hat.com>,
	"Rusty Russell" <rusty@...tcorp.com.au>
Subject: [047/121] virtio: console: return -ENODEV on all read operations
 after unplug

3.2.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Amit Shah <amit.shah@...hat.com>

commit 96f97a83910cdb9d89d127c5ee523f8fc040a804 upstream.

If a port gets unplugged while a user is blocked on read(), -ENODEV is
returned.  However, subsequent read()s returned 0, indicating there's no
host-side connection (but not indicating the device went away).

This also happened when a port was unplugged and the user didn't have
any blocking operation pending.  If the user didn't monitor the SIGIO
signal, they won't have a chance to find out if the port went away.

Fix by returning -ENODEV on all read()s after the port gets unplugged.
write() already behaves this way.

Signed-off-by: Amit Shah <amit.shah@...hat.com>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/char/virtio_console.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -637,6 +637,10 @@ static ssize_t port_fops_read(struct fil
 
 	port = filp->private_data;
 
+	/* Port is hot-unplugged. */
+	if (!port->guest_connected)
+		return -ENODEV;
+
 	if (!port_has_data(port)) {
 		/*
 		 * If nothing's connected on the host just return 0 in
@@ -653,7 +657,7 @@ static ssize_t port_fops_read(struct fil
 		if (ret < 0)
 			return ret;
 	}
-	/* Port got hot-unplugged. */
+	/* Port got hot-unplugged while we were waiting above. */
 	if (!port->guest_connected)
 		return -ENODEV;
 	/*

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