linux-kernel - Re: [PATCH net-next v6 2/5] net/lapb: support netdev events

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Date:   Wed, 25 Nov 2020 16:08:14 -0800
From:   Xie He <xie.he.0141@...il.com>
To:     Martin Schiller <ms@....tdt.de>
Cc:     andrew.hendry@...il.com, davem@...emloft.net, kuba@...nel.org,
        linux-x25@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v6 2/5] net/lapb: support netdev events

Hi Martin,

Since we are going to assume lapb->state would remain in LAPB_STATE_0 when
the carrier is down (as understood by me. Right?), could we add a check in
lapb_connect_request to reject the upper layer's "connect" instruction when
the carrier is down? Like this:

diff --git a/include/linux/lapb.h b/include/linux/lapb.h
index eb56472f23b2..7923b1c6fc6a 100644
--- a/include/linux/lapb.h
+++ b/include/linux/lapb.h
@@ -14,6 +14,7 @@
 #define	LAPB_REFUSED		5
 #define	LAPB_TIMEDOUT		6
 #define	LAPB_NOMEM		7
+#define	LAPB_NOCARRIER		8

 #define	LAPB_STANDARD		0x00
 #define	LAPB_EXTENDED		0x01
diff --git a/net/lapb/lapb_iface.c b/net/lapb/lapb_iface.c
index 3c03f6512c5f..c909d8db1bef 100644
--- a/net/lapb/lapb_iface.c
+++ b/net/lapb/lapb_iface.c
@@ -270,6 +270,10 @@ int lapb_connect_request(struct net_device *dev)
 	if (!lapb)
 		goto out;

+	rc = LAPB_NOCARRIER;
+	if (!netif_carrier_ok(dev))
+		goto out_put;
+
 	rc = LAPB_OK;
 	if (lapb->state == LAPB_STATE_1)
 		goto out_put;

Also, since we are going to assume the lapb->state would remain in
LAPB_STATE_0 when the carrier is down, are the
"lapb->state == LAPB_STATE_0" checks in carrier-up/device-up event
handling necessary? If they are not necessary, it might be better to
remove them because it may confuse people reading the code.