From 44a049c42681de71c783d75cd6e56b4e339488b0 Mon Sep 17 00:00:00 2001
From: Xie He <xie.he.0141@gmail.com>
Date: Wed, 2 Sep 2020 17:06:58 -0700
Subject: [PATCH] drivers/net/wan/hdlc_fr: Add needed_headroom for PVC devices

PVC devices are virtual devices in this driver stacked on top of the
actual HDLC device. They are the devices normal users would use.
PVC devices have two types: normal PVC devices and Ethernet-emulating
PVC devices.

When transmitting data with PVC devices, the ndo_start_xmit function
will prepend a header of 4 or 10 bytes. Currently this driver requests
this headroom to be reserved for normal PVC devices by setting their
hard_header_len to 10. However, this does not work when these devices
are used with AF_PACKET/RAW sockets. Also, this driver does not request
this headroom for Ethernet-emulating PVC devices (but deals with this
problem by reallocating the skb when needed, which is not optimal).

This patch replaces hard_header_len with needed_headroom, and set
needed_headroom for Ethernet-emulating PVC devices, too. This makes
the driver to request headroom for all PVC devices in all cases.

Cc: Krzysztof Halasa <khc@pm.waw.pl>
Cc: Martin Schiller <ms@dev.tdt.de>
Signed-off-by: Xie He <xie.he.0141@gmail.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 drivers/net/wan/hdlc_fr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wan/hdlc_fr.c b/drivers/net/wan/hdlc_fr.c
index 9acad651ea1f6..12b35404cd8e7 100644
--- a/drivers/net/wan/hdlc_fr.c
+++ b/drivers/net/wan/hdlc_fr.c
@@ -1041,7 +1041,7 @@ static void pvc_setup(struct net_device *dev)
 {
 	dev->type = ARPHRD_DLCI;
 	dev->flags = IFF_POINTOPOINT;
-	dev->hard_header_len = 10;
+	dev->hard_header_len = 0;
 	dev->addr_len = 2;
 	netif_keep_dst(dev);
 }
@@ -1093,6 +1093,7 @@ static int fr_add_pvc(struct net_device *frad, unsigned int dlci, int type)
 	dev->mtu = HDLC_MAX_MTU;
 	dev->min_mtu = 68;
 	dev->max_mtu = HDLC_MAX_MTU;
+	dev->needed_headroom = 10;
 	dev->priv_flags |= IFF_NO_QUEUE;
 	dev->ml_priv = pvc;