linux-kernel - [PATCH net] drivers/net/wan/x25_asy: Correct the ndo_open and ndo

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Date:   Tue, 22 Sep 2020 06:57:18 -0700
From:   Xie He <xie.he.0141@...il.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, Martin Schiller <ms@....tdt.de>,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Cc:     Xie He <xie.he.0141@...il.com>
Subject: [PATCH net] drivers/net/wan/x25_asy: Correct the ndo_open and ndo_stop functions

1.
Move the lapb_register/lapb_unregister calls into the ndo_open/ndo_stop
functions in x25_asy_netdev_ops.
This makes the LAPB protocol start/stop when the network interface
starts/stops. When the network interface is down, the LAPB protocol
shouldn't be running and the LAPB module shoudn't be generating control
frames.

2.
Move netif_start_queue/netif_stop_queue into the ndo_open/ndo_stop
functions in x25_asy_netdev_ops.
This makes the TX queue start/stop when the network interface
starts/stops.

3.
The x25_asy_close function was originally used as the ndo_stop function.
However, I think when stopping the interface we shouldn't do the things
that this function does (except netif_stop_queue).
 1) We shouldn't clear TTY_DO_WRITE_WAKEUP and set sl->xleft to 0,
    because this may cause the transmission of the last frame before
    stopping to be incomplete.
 2) We shouldn't set sl->rcount to 0,
    because if we stop the interface and quickly start it again,
    the first frame we receive could be incomplete.
So I moved it to make it be called in x25_asy_close_tty (when closing
the TTY line discipline) instead. (This also makes the code look better
because x25_asy_open is called in x25_asy_open_tty.)

Cc: Martin Schiller <ms@....tdt.de>
Signed-off-by: Xie He <xie.he.0141@...il.com>
---
 drivers/net/wan/x25_asy.c | 42 +++++++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 17 deletions(-)

diff --git a/drivers/net/wan/x25_asy.c b/drivers/net/wan/x25_asy.c
index 7ee980575208..88a73ce6d9f4 100644
--- a/drivers/net/wan/x25_asy.c
+++ b/drivers/net/wan/x25_asy.c
@@ -464,7 +464,6 @@ static int x25_asy_open(struct net_device *dev)
 {
 	struct x25_asy *sl = netdev_priv(dev);
 	unsigned long len;
-	int err;
 
 	if (sl->tty == NULL)
 		return -ENODEV;
@@ -490,14 +489,7 @@ static int x25_asy_open(struct net_device *dev)
 	sl->xleft    = 0;
 	sl->flags   &= (1 << SLF_INUSE);      /* Clear ESCAPE & ERROR flags */
 
-	netif_start_queue(dev);
-
-	/*
-	 *	Now attach LAPB
-	 */
-	err = lapb_register(dev, &x25_asy_callbacks);
-	if (err == LAPB_OK)
-		return 0;
+	return 0;
 
 	/* Cleanup */
 	kfree(sl->xbuff);
@@ -519,7 +511,6 @@ static int x25_asy_close(struct net_device *dev)
 	if (sl->tty)
 		clear_bit(TTY_DO_WRITE_WAKEUP, &sl->tty->flags);
 
-	netif_stop_queue(dev);
 	sl->rcount = 0;
 	sl->xleft  = 0;
 	spin_unlock(&sl->lock);
@@ -604,7 +595,6 @@ static int x25_asy_open_tty(struct tty_struct *tty)
 static void x25_asy_close_tty(struct tty_struct *tty)
 {
 	struct x25_asy *sl = tty->disc_data;
-	int err;
 
 	/* First make sure we're connected. */
 	if (!sl || sl->magic != X25_ASY_MAGIC)
@@ -615,11 +605,7 @@ static void x25_asy_close_tty(struct tty_struct *tty)
 		dev_close(sl->dev);
 	rtnl_unlock();
 
-	err = lapb_unregister(sl->dev);
-	if (err != LAPB_OK)
-		pr_err("%s: lapb_unregister error: %d\n",
-		       __func__, err);
-
+	x25_asy_close(sl->dev);
 	tty->disc_data = NULL;
 	sl->tty = NULL;
 	x25_asy_free(sl);
@@ -722,15 +708,37 @@ static int x25_asy_ioctl(struct tty_struct *tty, struct file *file,
 
 static int x25_asy_open_dev(struct net_device *dev)
 {
+	int err;
 	struct x25_asy *sl = netdev_priv(dev);
 	if (sl->tty == NULL)
 		return -ENODEV;
+
+	err = lapb_register(dev, &x25_asy_callbacks);
+	if (err != LAPB_OK)
+		return -ENOMEM;
+
+	netif_start_queue(dev);
+
+	return 0;
+}
+
+static int x25_asy_close_dev(struct net_device *dev)
+{
+	int err;
+
+	netif_stop_queue(dev);
+
+	err = lapb_unregister(dev);
+	if (err != LAPB_OK)
+		pr_err("%s: lapb_unregister error: %d\n",
+		       __func__, err);
+
 	return 0;
 }
 
 static const struct net_device_ops x25_asy_netdev_ops = {
 	.ndo_open	= x25_asy_open_dev,
-	.ndo_stop	= x25_asy_close,
+	.ndo_stop	= x25_asy_close_dev,
 	.ndo_start_xmit	= x25_asy_xmit,
 	.ndo_tx_timeout	= x25_asy_timeout,
 	.ndo_change_mtu	= x25_asy_change_mtu,
-- 
2.25.1